Matt Chung's Site

Author: mattchung

Daily Review – Day ending in 2020/08/31
Yesterday

Most interesting part of yesterday was a 1 on 1 video Chime chat that my co-worker scheduled with me. What started off with me stepping through our code base (for a set of features I added to the dataplane) morphed into a lengthy discussion around mental health and burning out and the idea of feeling confident in our own abilities. They had shared with me that they were starting to feel physically ill and after paying visits to the doctor for a full body check up, they discovered their symptoms manifest from mental health issues.

I’m very familiar with these feelings and can empathize.

In turn, I shared that I prioritize mental health and well being above all else and that I attend weekly therapy sessions (for the past four years) to deal with very similar issues that they are encountering: learning how to set boundaries, learning how to believe in oneself (i.e. imposter syndrome). It’s not as if I’ve completely overcome and mastered these problems; in fact, I wrestle with these issues — every day — but I now have have tools and data points to support me.

Although I love working as a software engineer, I sometimes wonder if I would pivot into a position or line of work where I can directly help people. It feels meaningful.

Writing
- Kept up with my writing cadence, publishing two small blog posts (a daily review and summary notes for the SPIN operating system structure)
Music
- Sang and played my own original guitar song I titled “Elliott’s in the house” for little Elliott while she was bouncing up and down on the couch while dinner, her mom guiding spoon fulls of avocado and noodles in her dime sized mouth
Graduate School
- Read first paper “SPIN”, performing a first pass on the paper (good to reinforce the learning material since there’s so much information packed into the lectures)
- Finished watching lectures on “Introduction to Virtualization” (learned that with paravirtualization, less than 2% code modification is necessary to integrate nicely with the underlying hypervisor)
Work
- Represented my team at the weekly operations meeting for my organization, stepping through all the high severity issues that I encountered and how they affected our metrics
- Finished a first draft of my design document, a paper that I am presenting to my organization today
- Met with a colleague of mine and confirmed that he will be participating in my fireside chat that I am organizing on behalf of Asians@ Amazon (I’m on the professional and development committee)
Family
- Gathered all the necessary documents (e.g. 2 months of pay stubs, last 2 years of W-2, etc) to submit to our lender since we needed to send an offer in for a house by today and needed a preapproval letter.
Today

Organization
- Plan day and week out by reviewing OmniFocus forecast events
- Process e-mail inbox down to zero
- Migrate sticky notes (written down while walking dogs in the morning) into writing tracker and OmniFocus
Graduate School
- Begin second series of lectures for advanced operating systems, lectures on “Memory Virtualization” (exciting stuff, I think)
Work
- Polish one pager design document for work and present
- Review dashboard in preparation for organization wide, weekly operations meeting
Family
- Morning routine of walking dogs at local Northacres park, blending a strawberry and banana smoothie (wait: no much coconut milk so that’s out of the question), eating lunch together, bathing Elliott as part of her night time routine
- Put together loan documents so that we can get a pre-approval for house that we are putting an offer in
Word of the day

insolent – adjective (adj) – showing a rude and arrogant lack of respect.

My strict teacher does not tolerate insolent behavior in her classroom

What are you grateful for?

I’m glad I’m writing down what I’m grateful for because its so easy for me to get trapped inside my own brain, my own world, when work (on call specifically) feels like a tornado.
- Jess being an amazing mom (so patient, so communicative) and leading parenting my example
Feelings
- I had lamented and avoided writing a paper at work and realized, after setting ink on paper for just a few minutes, I actually enjoyed the task but had to overcome my own fear of “not knowing enough” or “looking stupid” in front of my colleagues
- As mentioned above in the summary, I feel good when I can help and serve others. Not in a purely intellectual way, but mentally and emotionally. This is important and perhaps will steer me in a new (or same or different) direction with my career
September 1, 2020
Advanced Operating Systems – OS Structure – Exokernel

Unlike the SPIN OS Structure, exokernel approaches extensibility by decoupling the authorization to hardware from its actual use, by using something called secure bindings. OS libraries will request secure bindings, the Exokernel returning an encrypted key that grants that particular service to specific resources.

One other way that the exokernel manages these underlying OS services is via CPU scheduling. The exokernel maintains a linear vector “time slots”, allotting each OS service a certain amount of time to run on the CPU.

Exokernel also introduces the concept of a STLB (software translation lookaside buffer), the STLB improving performance since, during each process context switch, the exokernel will copy the hardware TLB to a software TLB structure and when the process runs again, the exokernel will copy the software TLB back into the hardware, eliminating the need for a TLB flush.

Exokernel Approach to Extensibility

Summary

Library OS requests access to a specific hardware resource. If access granted, exokernel returns an encrypted key which will be used for future keys

Examples of Candidate Resources

Summary

An OS library will perform some action, sending the Exokernel its encrypted key, and once Exokernel accepts that request, the data processing is cheap. Like packet processing: OS library requests to install predicates for packet filtering; once predicates installed, exokernel will invoke those rules on behalf.

Implementing Secure Bindings

Summary

There are three mechanisms for implementing secure bindings. First is hardware mechanisms, like fetching the TLB. Second would be software, like caching the hardware TLB inside of the OS, avoiding the cost of flushing the TLB during a context switch. And third would be downloading code into the kernel, a feature analogous to SPIN’s approach with logical domains. I don’t really understand these concepts quite yet: it’s all a bit abstract, for now.

Default Core Services in Exokernel

Default Core Services in Exokernel

Summary

For memory management, the library OS will handle the page fault (uncalled through the register) by presenting a mapping (with the secure binding) to the Exokernel, the Exokernel installing the mapping in the TLB (hardware), this step requiring privileged access.

Secure Binding

Summary

As the instructor put it, this is all a bit dicey. Both SPIN and Exokernel allow library OS privilege for pure performance but how do we guarantee that the insertion of code into the kernel is done … securely? Safely? Will find out soon, probably over the next couple videos

Memory Management using Software TLB

Software TLB

Summary

In exokernel, during a context switch, the hardware TLB for a process is copied into a STLB (software TLB) and during a context switch, new process’s software TLB will be preloaded by the Exokernel. Of course, if there’s a TLB cache miss, then the standard page fault workflow happens

Default Core Services in Exokernel (continued)

Default Core Services continued

Summary

Three is a linear vector of “time slots”, each OS service reserving a slot for its service. If the OS service runs longer than the allotted quantum, the exokernel will punish it, reducing its time slot in the next run. Time is bounded to perform the saving of the context.

Revocation of Resources

Summary

Exokernel can revoke or reclaim permission from a Library OS, the OS sending an up call (and passing a repossession vector) to the Library OS, informing the library OS that it may need to stash away its resources (on disk).

Putting it all together

Summary

While a library OS’s thread is running, an external event will be kicked up to the running process to determine what to do next

Exokernel Data Structures

Exokernel Data Structures

Summary

Exokernel maintains a data structure for each of the running library OS, maintaining a software TLB that gets loaded during a context switch

Performance Results of Spin and Exokernel

Summary

Absolute numbers are meaningless: it’s the trends that count.

September 1, 2020
Advanced Operating Systems: The SPIN Approach

What did I learn? What are the main takeaways?

The concept of border crossing pops up over and over again. This is a new term I never heard of prior to this class. The term is almost synonymous to a context switch but it is subtly different in the sense that a context switch (switch from one process to another or one thread to another) can occur without a border crossing, without changing the underlying hardware address space.

SPIN attempts to enforce protection at the compiler level, by using a restrictive language called Modula-3. Unlike the C language, where you can cast a pointer to whatever data structure you like, Modula-3 enforces type safety, only allowing the developer to cast a pointer to specific types of data structures that they had already specified earlier in the code.

SPIN offers extensibility by allowing different types of OS services to co-exist with one another.

But what are the trade offs with SPIN, when compared with Microkernel and Exokernel?

It appears that SPIN would be more performant than Microkernel due to no border crossings while maintaining flexibilty (multiple types of OS services that cater to application processes) and security (via logical protection domains) with Modula-3, allowing code OS services library code to co-locate with kernel code.

Introduction

Customizing OS with SPIN

Summary

SPIN and Exokernel take two different paths to achieving extensibility. These designs overcome the issue of Microkernel, which compromises in performance due to border crossings, and monolithic, which does not lend itself to extensibility

What we are shooting for in OS Structure

Summary

We want flexibility similar to a microkernel based approach but also want protection and performance of monolithic. We want the best of both worlds: performance protection flexibility

Approaches to Extensibility

Damn, this is a super long video (8 minutes, compared to the other one to two minute videos prior)

Capability based

Hydra OS (1981)

Summary

Hydra did not fully achieve its goal of extensibility

Micro Kernel Based

Summary

Performance took a back seat, since the focus was on extensibility and portability. Bad press for micro kernel based due to the twin goals.

SPIN approach to extensibility

Summary

By co locating the kernel and extension in the same hardware space, the extensions are cheap as procedure call. Doing this by depending on a strongly typed language to provide safety

Logical Protection Domains

Summary

Using a programing language called Modula3, which doesn’t appear to be popular in practice, we can enforce protection at the logical level. This programming language, unlike C, restricts casting pointers to random data structures, only allowing the cast to a particular data type.

Spin mechanisms for protection domains

Summary

The secret sauce of protection and performance are the mechanisms of creating (i.e. expose entry points), resolving (i.e. leverage other entry points), and combining of logical protection domains

Customized OS with Spin

Another example of SPIN os customization

Summary

There can be multiple file systems (written in Modula3), each file system catering to their callers, and each file system using the same underlying hardware address space. And they can share modules with one another, like the networking entry point.

Example Extensions

Summary

Example of Unix Servers implementing their OS on SPIN as well as a video server / display client building on top of spin

Quiz: Border Crossings

Quiz: Least likely for border crossing

Summary

Microkernel and SPIN offer performance since they limit the border crossings. In SPIN, Logical domains do not require border crossings

SPIN Mechanisms for Events

SPIN classifies three types of event handling: one-to-one, one-to-many, many-to-one

Summary

To handle events (like packet arrival) we can have a 1:1 mapping, 1:N mapping or N:1 mapping. For 1:1, an example would be an ICMP packet arriving and the 1 ICMP handler running. In a 1:N mapping, the IP packet arrived event runs and signals three other event handlers like ICMP, UDP, or TCP. Then finally, there is a N:1, and an example of this is an Ethernet and ATM packet event arrives but both funnel into the IP handler

Default Core Services in SPIN

Summary

SPIN offers core services like memory management, CPU scheduling etc. And SPIN will provide a header file that OS programmers need to implement. Remember: these implementations talk to each other through well defined interfaces, offering protection, but are also performant cause there are no border crossings)

Default Core Services in SPIN (Continued)

Summary

Provides primitives, the interface function definition. The semantics are up to the extension itself. SPIN makes sure extensions get time on scheduler

August 31, 2020
Daily Review – Day ending in 2020/08/30
Yesterday

Writing
- Wrote and published an article on Time Management Tip #1: Pomodoro Technique. How I use the technique and how I’ve adjusted it to fit my needs.
Music
- Had my bi-weekly virtual guitar lesson with Jared. This was the first lesson back, after he took a 1.5 month sabbatical, a vacation he deserves and a vacation that he takes once a year. During the lesson, we didn’t actually focus on any mechanics of guitar this time, which was fine by me because instead, we had a lengthy discussion around where we want to take guitar lessons: what’s the point and what do I want to work towards. More on this in a separate blog post.
Graduate School
- Submitted both homework assignments (apparently a day before it was due: so hooray me) and watched the video lectures while sitting in the back seat of the car, while my wife drove us from Seattle to Renton (see house hunting below, under family section).
Organization
- Miss: I had a scheduled call at 06:00 PM PST with a fellow class mate and I missed the chat. For two reasons: my phone died on the way home and two the event was not scheduled in my calendar, no alerts or notifications. Fortunately, he was still online at the time so we were able to meet over Google Hangouts despite me being 30 minutes late or so.
Family
- House hunted in Renton, viewing three homes and one of which we will submit an offer. We’ll go in at listing price and per our realtor, a friend of my sisters, escalate to about 20k above if there are competing offers. I could really see Jess and I living in the home, the square footage practically doubling the size of our current rental. Funny how having kids changes things. Up until a week or two ago, I opposed the idea of moving to the suburbs, opposed to moving away from Maple Leaf/North Seattle: all favorite local cafes are within walking distance, the amazing off leash dog parks like Magnuson, top notch vegan restaurants. But since COVID hit, my view has changed. Based off of the amount of time we spend at home, which is about 23 out of the 24 hours in the day, I’d love for Elliott to have a little more space, more than the 15 square feet of crawling space that we have now.
Today

Organization
- Plan day and week out by reviewing OmniFocus forecast events
- Process e-mail inbox down to zero
- Migrate sticky notes (written down while walking dogs in the morning) into writing tracker and OmniFocus
Graduate School
- Begin on lecture series for the week, the lecture focusing on virtualization (curious what this means)
- Write up notes taken over the weekend on L3 Microkernel, SPIN, and Mach, three different underlying OS structures, each with their own trade offs
Work
- Finish one pager design document (due tomorrow)
- Review dashboard in preparation for organization wide, weekly operations meeting
Family
- Morning routine of walking dogs at local Northacres park, blending a strawberry and banana smoothie (wait: no much coconut milk so that’s out of the question), eating lunch together, bathing Elliott as part of her night time routine
- Put together loan documents so that we can get a pre-approval for house that we are putting an offer in
Bonus Image

Elliott standing up at the beach

Word of the day

decry – adjective (adj) – publicly denounce

“SPIN and Exokernel used Mach as a basis for decrying Microkernel-based design”

What are you grateful for?

I’m glad I’m writing down what I’m grateful for because its so easy for me to get trapped inside my own brain, my own world, when work (on call specifically) feels like a tornado.
- To be in a financial position to even be looking to buy a home in the midst of COVID-19
Feelings
- Nervous about the move. Just like Jess. Leaving behind North Seattle is scary: we’ve grown to love the city. Will we regret it? Maybe. But the way I see it is that this decision (of moving to Renton) is not a one-way door: we can always move back and rent in North Seattle. Sure, we might not get the same awesome rental that we been living in for 4+ years but that’s a fair trade off. We are doing the right thing by listening to our gut and being heedful to our fears.
August 31, 2020
Weekly Review – Week ending in 2020/08/30
- Writing
  - Developed a manageable cadence of blogging a single blog post every day, most of them daily reviews or notes taken during advanced operating systems
  - Writing the daily reviews (each entry eats up about 15 minutes of my morning) help me not only plant my two feet in the ground and settle for the day, but provide the necessary content for my weekly review / reflections. Will likely continue this new habit (assuming I still wake up between 04:30 and 05:00 AM)
- Music
  - Recorded a short little melody and harmony on my iPhone while playing guitar for Elliott and Jess during lunch. Super simple melody and chorus lyrics go “It’s a sad song, it’s a love song”
- Graduate School
  - Felt proud of myself for being able to connect the dots between theory and practice, catching the relationship between C code I write at work and what I read in the textbook (revolving around virtual private numbers using a bit mask and SHIFT operations)
  - Glad I was able to keep up with all the lectures, although I could’ve finished them much earlier in the week. But I spent an hour on deep diving into virtually indexed physically tagged cache, a topic I could’ve just glossed over but I just couldn’t let go of not understanding the topic
  - Completed writing up the homework assignment, typing it all up took much longer than anticipated due to formatting issues when copying between OmniOutliner and Microsoft Word
- Organization
  - Ripped apart three books and scanned them using my ScanSnap. Again, I’ve nailed down the process since on average, it takes about 8 minutes from running the knife down the spine of the book to the moment the last (200+ page) book scans to my DevonThink system
- Physical and Mental Health
  - Cancelled my weekly psychotherapy session, a session I often look forward to since I’ve been attending just about every week for close to 5 years now
- Family
  - Lots of administrative duties this week, including replacing the punctures front left tire at Discount Tires, chopping up all the freshly bought vegetables and storing them away in reusable Stasher bags, driving from Seattle to Renton to visit my mom who is visiting from California for a few days
Misses
- Not a single day of exercise. This habit fell off the wagon about 2 months ago (or was it 3 or 4) when I injured the sole of my left foot. I was unable to shift any weight to my foot without wincing in pain. But the food healed about 2 months ago and I need to re-establish a habit of exercising: even if it is running for 10 minutes or stretching for 5.
- Being on call really zapped the joy out of my week. For starters, I was unable to break away from the laptop while my mom was in town, not getting to spend much quality time with her. This event, along with waking up at 12:00AM and 3:00 AM throughout the week makes me re-evaluate the team I am on and wonder a team with less operational burden might make sense for my health
Photos of the week

Jess, Matt, Elliott with sun in the background, three of us walking dogs at the park early in the morning

Llttle Elliott at carcreek park, who is starting to not look so little anymore

Reflections

Jess pointed out that when I am on call, I’m a little more edgy, a little less patient. She’s probably right because during the week, I’m constantly getting interrupted with operational issues, requiring me to drop whatever I’m doing — studying, hanging out with my wolf pack — and turn my attention towards work.

Although tiring, the early morning reflections and study sessions are proving to be valuable. I’m able to crank out a ton of work, crossing off graduate school and personal writing before anyone in the house hold wakes up. Being a productive in the morning, even if its just a little, really sets me in a better mood thorughout the day, my mind free to concentrate on the present moment instead of thoughts of “should’ve done this … and this” occupying CPU cycles in my brain.

Graduate school is tough but rewarding and such a privilege. I happened to stumble upon my blog post from 2018, almost 2 years ago to date, when I just got admitted into the graduate program: I was ecstatic to learn about computer science. I still am. And need to continue with my balancing the following: learning deeply (the main point of returning back to graduate school) and just getting things done (I have a family now, so time is very precious).

Realized that checking my work laptop first thing in the morning for just that one little thing doesn’t work: I get sucked in and begin tackling other items, including checking my e-mail inbox, or slack messages, or whatever. So my rule of thumb is to not flip open the lid of my work laptop until I am ready to fully work

My noise wrinkles every time I see the photo of Elliott crawling in the back seat of the Ford Escape. The picture zooms in on face. I only see pure joy and beauty in her. It really is such an honor to be a father, to be in a position to see her develop and witness her mom basically perform mom magic every day.
August 30, 2020
Selecting research papers to read for Advanced Operating Systems
For advanced operating systems course, us students are required to sign up for (at least) two research papers that we summarize. Although two papers doesn’t sound like much, many former students of the course suggested ignore the other research papers and instead, focus on watching the lectures (which do cover the papers, sort of), banging out the software project, and (sadly) performing rote memorization based off of previous exams (I’ll need to get my Anki set up for this, stat).

Reviews on OMSCentral related to reading papers

I gave up on trying to read all the papers, electing to focus on projects and memorize the lectures instead. It worked out ok for me, and I averaged 18 hours a week on this course anyway. YMMV.

The downside to me is the number of readings was, well, high. Somewhere around 45 papers are to be read during the semester, and most of them are foundational but also from an earlier time in computing. I enjoy newer research papers with tech I can relate to, so for me in general these were less enjoyable and more difficult to digest. Still worthwhile, I think, but more of a slog.

The sheer number of papers assigned could easily push the time commitment past 30 hours a week if a student were to read them all, but as most have noted, you can largely skip reading them. Even skipping papers, the lectures are long and are difficult to get through. The content is broad and I think it tries to cover too much ground.

Papers I’m going to read

So although I’ll probably skim most of the research papers, I’ll dig into the below papers in depth. Why did I choose these papers? Well, some of the other papers (on networking) played into my strengths, categories that I’m somewhat well versed on. As a result, I chose papers grouped under categories that I not only find interesting (distributed systems and failures + recovery mechanism) but categories I’m unfamiliar with.
- Liu, Kreitz, van Renesse, Hickey, Hayden, Birman, Constable, “Building Reliable High Performance Communication Systems from Components “, 17th ACM Symposium on Operating System Principles, OS Review, Volume 33, Number 5, Dec. 1999.
- D. Porter, O. Hofmann, C. Rossbach, A. Benn, E. Witchel, “Operating System Transactions“, SOSP’09.
Stretch goal
- Lamport, L., “Time, Clocks, and the Ordering of Events in a Distributed System”, Communications of the ACM, 21, 7, pgs. 558-565, July 1978.
References
1. Student Review – https://omscentral.com/review/-M7Z0y3X-ORUdktU4bqT
2. Student Review – https://omscentral.com/review/-M74QupA7ND5_xq-cY2Z
3. Student Review – https://omscentral.com/review/-M69xss3dGXWiXXft9Ha
4. Sign up link
August 29, 2020
My time management tip #1 – Pomodoro Technique
Since the pandemic hit the states back in February this year, I’ve been working remotely from home (such a blessing and a serious privilege). Working from home underscores the importance of time management, especially for someone like me who can either deeply fall into work mode for hours and hours (never breaking eyes away from screen) or scroll mindlessly on websites like Hacker News or Reddit. The former melts my mental health and the latter kills my productivity.

So to avoid either scenario — working too long or not working at all — I employ a Pomodoro technique¹. The pomorodoro technique, which I picked up years ago when taking Learning How to Learn Course on Coursera, was invented in the early 1990s by Franscesco Cirillo. The basic premise is this: you set a timer for 25 minutes and work deeply for those 25 minutes. Once the alarm sounds, you break. The idea is that the technique improves your focus and promotes giving your brain some time off to relax.

So how do I use the Pomorodo technique in practice? What does it look like?

I use a kitchen timer, the TIMER YS-390 to be specific. This model hits all of my own personal requirements. The device has a dual count timer. I set the top timer to 50 minutes (my personal period of deep focus) and the bottom for 10 minutes; the 10 minutes is my grace period, allowing me to ease into my work (basically I cut myself some slack here). In addition to the dual timers, the alarm’s volume can be adjusted: no sound, low, high. I typically set the volume knob on low as to not frighten my daughter awake when she’s sleeping (my dentist’s rule: never wake a sleeping baby). And finally, the third feature I love is the physical cue. When either of the timers hit zero, the little button begins flashing red like a cop car. This makes it difficult to ignore and I find it really forces my eyes to break away from the screen.

So what happens when the timer sounds the alarm? I start by silencing it, hitting the silicone start/stop button, stepping away from the computer and if I’m lucky enough, take a 5-10 minute break with either my baby daughter (who is growing up way too fast) or wife or dogs (or if I’m really lucky, all four of them). This break, is also no exception, but instead of using my TIMER YS-390, I set a countdown alarm on my G-Shock watch.

Do I always break at the very moment the alarm sounds?

No. Sometimes I find that I’m really in the flow (for work or for graduate school or for writing on this blog) so what I do instead is quickly press the bottom right button, resetting the 10 minute timer. This allows me another grace period of deep work. It’s okay to not be so rigid and cut yourself some slack.

References
August 29, 2020
Daily Review – Day ending in 2020/08/27
What’s your chief aim for today

Learning that while I’m on call for my team, I very rarely hit my targets for the day (see section on “How did yesterday go”). Not only that, but I’m drained by the end of the day, little to no CPU cycles left for studying (although this window of time is ripe, since Elliott is asleep). Nonetheless, I’ll still call out what I want to accomplish today since these little tasks, when added together, help me fulfill my long term goals (a separate page for this will be pinned up on my blog soon).
- Writing
  - Write and publish one piece on this blog
- Graduate School
  - Complete typing up answers for assignment #1
  - Edit answers for pre-lab assignment
  - Watch and take notes on second module in advanced operating systems (Lesson 2)
- Organization
  - Review Inbox items sitting in OmniFocus
  - Scan projects sitting in my OmniFocus
- Work
  - Continue to chip away at writing one-pager design for a prototype for new feature at work
  - Survive today’s on call and flurry of operational issues that may arise
How did yesterday go?

Basically, when I’m call, the entire day is blurry, the day flashing by right before my eyes. During the day, I’m in a completely different state, a reactive mode, dealing with whatever gets thrown at me from auto cut tickets to Chime messages or Slack messages or e-mails. Chaotic days like this put me in a despondent state.
- Another emotionally draining day, thanks to the on call operations for the week. I got paged at 12:00 AM and after troubleshooting for about half an hour, I was unable to fall back asleep for at least another 45 minutes. When getting woken up in the middle of the night, I find that there’s a very small window — about 15 minutes — in which I can fall back asleep. After that amount of time has elapsed, falling back asleep requires serious deep breathing
- Because of the interrupted sleep, I was unable to wake up early and use that morning slot to squeeze in studying before work. I’ll borrow back some time during the day to make up for it though. Oh yea, I also am a bit flustered that I was unable to comfortably hang out out with my daughter and wife and dogs because I did end up getting paged this morning (at around 07:00 am). Fortunately, we had already walked at the park so I was nearby my laptop: so no breach in service level agreement (SLA).
- Did not get to put any study time in (as mentioned above) so I’ll need to carve out time today to catch up with watching videos lectures and typing up my homework assignment for advanced operating systems.
Word of the day

remiss – adjective (adj) – lacking care or attention to duty; negligent.

“it would be very remiss of me not to pass on that information”

What are you grateful for?

I’m glad I’m writing down what I’m grateful for because its so easy for me to get trapped inside my own brain, my own world, when work (on call specifically) feels like a tornado.
- My German Shepherd dog (Metric) is in good health (she eats raw, gets daily exercise) and behaves wonderfully with my daughter. I do feel a pang in my heart when I notice small signs that she’s aging, signs like an additional grey whisker sprouting out.
- Jess ordering two delicious vegan sandwiches for lunch, sandwiches glazed with moist hummus and filled with soft chick peas. Yummy.
Feelings
- As mentioned above, on call operations for my team (and many other teams in Amazon) can drain every ounce of energy. Every time my phone sounds an alarm, my body releases cortisol and stress washes over me. Granted, there are some weeks where very little issues crop up: but that’s the not the norm as of late. But is this how I want to live my life 24×7, once every 5-6 weeks? Sure, the work is rewarding and challenging and intellectually stimulating but one entire week of pure exhaustion may not be worth the cost
- Seeing my wife watch over both my daughter and niece (Maiya) sends butterflies to my stomach. She’s patient and gentle with them, two important qualities for anyone.
References
1. https://www.theatlantic.com/culture/archive/2020/08/lovecraft-country/615259/
August 28, 2020
Thinking out loud – Not fully understanding virtually indexed physically tagged (VIPT) details
I’m really struggling to intimately understanding virtually index privately tagged concept. From a high level, I get that VIPT is an optimization technique, parallelizing both the translation of virtual addresses to physical and the cache look up of the physical address. This seems impossible at first since the cache depends on the physical frame number (PFN).

So in order to accomplish this, we’ll use the some bits of the VPN to search in the TLB and then the least significant bits when searching the cache. This makes sense. But what I don’t quite fully don’t understand is why we have to limit the size of the cache in order to avoid aliasing (i.e. different virtual addresses that end up mapping to the same physical frame).

Thinking out loud here … I suppose that if the index of the physical bits bleed into the virtual address, then we actually do not avoid the aliasing problem, the issue of having more than one virtual address map to the same physical frame.

Ok, I think I got it.

But what’s the catch?

You only can have a very small cache, the size equal to the page size multiplied by the set associativity. This means that the only way to increase the size of the cache is by increasing the associativity which ultimately increases the look up time as well since the cache has to look the tag up across multiple cache lines.

Reference
1. https://cs.stackexchange.com/questions/68492/does-the-aliasing-problem-show-up-in-a-virtually-indexed-physically-tagged-cache
2. https://cseweb.ucsd.edu/classes/fa10/cse240a/pdf/08/CSE240A-MBT-L18-VirtualMemory.ppt.pdf
August 28, 2020
Daily Review – Day ending in 2020/08/26
What’s your chief aim for today
- Writing
  - Write and publish one piece on this blog
- Graduate School
  - Complete typing up answers for assignment #1
  - Edit answers for pre-lab assignment
  - Watch and take notes on second module in advanced operating systems (Lesson 2)
- Organization
  - Review Inbox items sitting in OmniFocus
  - Quickly glance over project
- Work
  - Continue to chip away at writing one-pager design for a prototype for new feature at work
  - Survive today’s on call and flurry of operational issues that may arise
How did yesterday go?
- Realized that checking my work laptop first thing in the morning for just that one little thing doesn’t work: I get sucked in and begin tackling other items, including checking my e-mail inbox, or slack messages, or whatever. So my rule of thumb is to not flip open the lid of my work laptop until I am ready to fully work
- Work drained me. All the back to back operational issues not only enervated me but derailed my entire day, something I should just expect since on call is so variable
- Being on call yesterday, I was unable to break away from the laptop while my mom was visiting Seattle, not getting to spend much quality time with her. Bummer. These feelings make me reevaluate work (see Feelings section)
Word of the day

underscore – verb (n) – to underline or to emphasize

Even Atlanta, Donald Glover’s Twin Peaks–esque FX series, toys with the supernatural and the surreal to underscore points about race made in its quieter moment¹.

In an internal memo, Stan Deal, chief executive of Boeing Commercial Airplanes and Greg Hyslop, Boeing’s chief engineer, sought to underscore the message that safety is the company’s top priority ²

What are you grateful for?
- My sister delivering a healthy little girl, her birthing free from any major complications (unless you consider an epidural a complication)
Feelings
- As mentioned above, on call operations for my team (and many other teams in Amazon) can drain every ounce of energy. Every time my phone sounds an alarm, my body releases cortisol and stress washes over me. Granted, there are some weeks where very little issues crop up: but that’s the not the norm as of late. But is this how I want to live my life 24×7, once every 5-6 weeks? Sure, the work is rewarding and challenging and intellectually stimulating but one entire week of pure exhaustion may not be worth the cost
- Seeing my wife watch over both my daughter and niece (Maiya) sends butterflies to my stomach. She’s patient and gentle with them, two important qualities for anyone.
References
1. https://www.theatlantic.com/culture/archive/2020/08/lovecraft-country/615259/
August 27, 2020