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You are viewing 25 entries, 25 into the past.

1st February 2019

6:14pm: Another good russian hard sci-fi novel
here. Thanks [profile] blau_kraehe for the hint. By the way, the same author also wrote a very good fantasy trilogy ("
Лестница из терновника").

27th January 2019

7:14pm: A very nice programming book
CTFP is a great book. I bought a hard cover and now I am reading it for the second time.

I have to, because first time I did not get it. First it reads easily as a gentle intro to monads, promising that monads are easy after you know the right terminology, then (almost in the end) it touches monads quickly, and then.. Please see the pic above. I did not understand anything from the last few chapters.

7th January 2019

1:41pm: Underwater: one short dive
I seen this structure, a sea cucumber, sea spider and a fish inside, so I decided to dive first and then glide slowly just above the seabed towards it, while making photos.

Once I came closer, the fish started looking at me cautiously:
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All pics taken during a short ~30 seconds dive at about only 2 meters depth.

29th December 2018

12:25pm: Underwater carribean
This time space for freediving was very limited: just 4 very small reefs and structures. Average depth was just 1.5 meters, with two deeper spots of 4 and 8 meters.

This fish was my host: it always followed me in the dives, was not afraid and was looking at me.
1.

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This time I have ~200 underwater pics after I filtered out another half thousand..

28th December 2018

3:51pm: Jacob Speaks: combinatorics
- Папа, а бывает так, что женщина болеет, и поэтому рожает больного ребенка?
- Да, конечно.
- А это всегда так, если мама болеет, то ребенок всегда рождается с такой же болезнью?
- Нет, необязательно. Бывает, что нет. Есть два случая: Мама болеет, ребенок родился здоровый, и мама болеет, ребенок больной.
..
- Папа, дай я что-то скажу! Не два случая, а четыре! Мама болеет, ребенок родился здоровый, мама болеет, ребенок больной, мама здоровая, ребенок здоровый, и мама здоровая, а ребенок больной. Так же тоже бывает?

И этот ребенок никак не может научиться считать до двадцати, и выучить остальные 24 буквы русского алфавита..

27th December 2018

1:58pm: Jacob Speaks: wedding
Jacob, 4y6m.
- Папа, я предложил девочке выйти за меня замуж и родить мне детей, когда мы вырастем. Но она отказалась!
- Наверное, ты ей не нравишься, или неправильно предложил. Ты как ей это сказал?
- Я сказал: Маша, когда мы вырастем, ты станешь моей мамой? А она ответила - нет, у тебя уже есть мама.

23rd December 2018

5:21pm: Vacation
Got back home from vacation.
We met several russian families there, and each and every time they heard us speaking russian, they switched to English or German. That was especially funny when their English was not very good. One of their families, when asked by someone: "What is your native languages?", answered: "My native language is 'ivrit' and we live in New York". (sic, "ivrit", not even Hebrew :). There was one guy who talked with us in good russian (just smalltalk on a beach), but he was from Bulgaria.

Also we were puzzled, when a pharmacist told us that "It is not a high season for Dengue fever yet, and even if it was, it is not a problem. You europeans bring us flu, and you can catch Dengue here, so all is fair.".

I guess in US there are no portraits of Obama on main town square. A bit south of US, there still is:

2nd December 2018

1:27pm: Jacob Speaks
Jacob, 4y5m
- Папа, давай поедем в Сибирь, на север!
- Зачем?
- Мы возьмем фонарик, лопату, дрель, и еще напечатаем на 3д-принтере кости мамонта. Приедем в сибирь, найдем, где ученые выкапывают кости мамонтов. Придем туда ночью с фонариком, и найдем сами кости мамонта. И заберем их в Мюнхен. А вместо настоящих костей положим наши пластмассовые. Пусть потом ученые думают, что это настоящие кости, и про них в телевизоре рассказывают!

30th November 2018

4:39pm: offline vpp
Achievement unlocked - I built and run vpp on a fully offline machine. Had to spend disproportional time on that, because it needs so many dependencies and dependencies of dependencies, and build system runs make,cmake,ninja,git,pip, some perl stuff - everything :) Like docker without docker..

29th November 2018

8:22am: Finally!
I am so glad that RHEL8 is 4.18 based! So tired of 3.10 oldies...
4.18 is very important for me because of nohz_full patches from 4.17, so rt-preempt is no longer a must to get a decent hard realtime system on general purpose linux host.

21st November 2018

9:59am: But why?
All Munich is now filled with billboards showing ads from Facebook and Google. They don't try to sell up google storage or facebook ads. They are simply informing that there are settings that enable restricting sharing posts with some of the friends.

Why? That must be a pretty expensive campaign, and I don't see any potential profit.

11th November 2018

11:14am: Autonomous driving
From a conversation with an old German engineer:
He: I don't understand why everyone tells that full autonomous driving will become common in just a few years. At current pace, certifying a fully autonomous system at the same level of scrutiny we use in automotive industry safety certification process will take more than a decade.
Me: Do you think a political decision to lower the standards just for autonomous driving is unlikely?

6th November 2018

9:23am: At last, some good book
The books I reviewed recently are mostly, I would say, non-orthodox. I am a bit embarrassed that I like reading this stuff, but here is something for a change.

"Цветы корицы, аромат сливы" is a great book by all accounts. There was a comment to one of my recent reviews that the Russian language used in all the books I mention (except Pelevin) is mediocre. This is true, but this book is the exception.

If you look at the author, her most prominent book is "Школа в Кармартене". I did not like that one. "Цветы корицы" share some good properties of "школа" like humor and language, but is a bit easier on a reader as there is actually some story, though still there is no villain.

31st October 2018

2:48pm: Diversity, Soviet Union
"Комиссия по расследованию" (1978)
A negative male character (Boyarskiy is acting), to a female engineer (positive character):
- Your eyes are beautiful, and your voice is charming. Is not that enough? Why would you need a career in engineering? You should use your strengths to fulfil your purpose!
- What is my purpose?
- In the end, the purpose of every woman is related only to her man.
- ???!
...
- OK, I am not your mom, but if she did not tell you, I will! Here is what will happen in five years: your boss, an old scientist, only needs you so there is a beautiful girl in his team. He will retire, and his place will be taken by a young and ambitious manager who will need good engineers. By that time you'll be older, and will loose both career and will not find a husband.
- I am not a beautiful girl in a team, I have all the required skills! And you are a moron.
- And you are a walking computer!

The movie was filmed at about the time when in West Germany they just allowed women to work without a written approval from a husband.

30th October 2018

12:38pm: Russian Clancy
Werewolf ( http://samlib.ru/a/afanasiev_a_w/, see flibusta for the full list ) had written several long series, "Tom Clancy style".

But I think only one of the series is actually interesting: "Наступление". The settings are 1982-1988, but Gorbachev [Spoiler (click to open)]was assassinated in 1986. Unlike his other series, this one is realistic. Unlike Tom Clancy, he shows respect to US forces. Most of the fights described in the series happens in Afghanistan. A lot of "заклепки, командирскаябашенка". Big part of the book are struggles between KGB, GRU and police in Soviet Union. It is great that there is no "попаданец" who wins WW3, that makes most of other books in the genre unreadable.

22nd October 2018

7:59pm: Jacob Speaks: German
Jacob, 4y4m.
- Папа, давай с тобой будем говорить по-немецки дома?
- Нет, мы с мамой и с тобой дома говорим по-русски.
- А если мы с тобой будем говорить по-немецки, то ты его быстро выучишь. Я тебе буду объяснять слова, которые ты не знаешь, и поправлять, когда ты неправильно произносишь. А то так и будешь как трусишка с немцами по-английски говорить. И еще ты станешь очень умный.
- А сейчас я не умный?
- Сейчас ты чуть-чуть умный, а когда выучишь немецкий язык, станешь очень умный. Вот я когда научусь читать и пойду в школу, тоже стану очень умный.

16th October 2018

1:20pm: Jacob Speaks: misunderstanding
- Вот вырасту, стану поваром! Буду печь торт. А еще я врагу в тарелку положу много грибов.
- Поганок наложишь врагу? Очень коварно.
- Нет, мама, поганки нельзя класть в овощное рагу!

1st October 2018

10:31am: Prefetchw
Prefetchw can be found in linux kernel source and windows kernel, but there is a trick: it was first added to AMD CPUs, and then once it appeared in Intel CPUs, it just stopped raising SIGILL, but nothing else happened.

Then eventually it was implemented properly, but I still get questions from customers on when it can be faster. Here is my last answer from an email:

On write, the cache line status turns to Modified, and turning to Modified from Exclusive state is faster than turning from Shared to Modified. PREFETCHW prefetches data to Exlusive state, so then when write happens later it can be faster. So if the cache line is fetched from DRAM, there is no difference.

25th September 2018

7:36pm: Beech nuts'2018
Because of the hottest summer I remember in Munich, this year's harvest of beech nuts is enormous.

So I found by experiment, why one should roast them before eating.

Just try eating a lot of non-roasted beech seeds :) (It is not bad for the stomach, don't worry :):) (evil laughter.)

12th September 2018

6:53pm: Jacob speaks: on unemployment
Jacob (4y3m old) noticed people are cutting thick grass stems that grow on tram tracks with scissors. He starts thinking aloud:

"Они стригут ножницами, чтобы трамваю было удобнее ехать. А почему бы им не стричь машиной? Тогда будут стричь быстрее... Но понадобится меньше людей для той же самой работы. А раз эти люди работают ножницами, наверное, они ничего больше не умеют делать. И поэтому не смогут найти другую работу. И придется им работать бомжами или бармалеями."

Should I tell him about AI replacing white collar jobs?

8th September 2018

12:40pm: Jacob Speaks: English song
- Папа, включи пожалуйста песенку, где поют - Katze Augen?
- ?
- Мама, папа не понимает, помоги!
- ОК, только поют там - Got to love you.

23rd August 2018

8:44am: Bug
Right now I am sitting in an airport on the way home and thinking about a bug I tried to find yesterday. Spent whole day with a customer but still have little clue.. I have proofs that the root cause is not in software, and not in hardware. So must be an interesting combination.

The bug manifests as random and rare events when a core stops for 12 microseconds. Full processor trace simply shows something like:
...
100.000000000: add r10, rax
100.000000000: test eax, eax
100.000000000: jnz 0x100
100.000012345: add rs1, 0x1
100.000012345: rdtsc
...
There are many reasons why a core might stop for ~10us (thermal, power, SMI, AVX2, turbo, C state, etc). However these causes leave a trace (and I seen none), and if that happens, the benchmark should be interrupted at a random place, not always at that jnz instruction.

JNZ instruction again cannot be a root cause either, because mispredict is 3 orders of magnitude lower than the delay we measure.

The issue happens more frequently on some CPUs and some cores within these CPUs - this points to a hardware root cause. However, when timer interrupts are active on that core, the issue happens and I see interrupt handler in the trace. If they are stopped, I don't see the interrupt handler in the trace, and issue happens. But when I disable timer interrupt on the core completely, the issue almost never happens. This points to software :)

20th August 2018

1:12pm: An outdoor swimming pool
A recent post reminded me of something: yesterday we went to a public swimming pool. Almost every Sunday we go to a swimming pool, and everywhere the mix of visitors is the same as mix of people I see in the city.

Except there is a swimming pool that is always very special (one we visited yesterday - Maria Eiselbad). All
the visitors there are europeans. (It is very busy on Sunday, like any other one).

I don't have a clue why is that. Public transport is there, price is the same as everywhere else. The only noticeable difference is that the water temperature is slightly lower than everywhere else, but that could hardly be the reason of that self-segregation. Any ideas?

8th August 2018

2:08pm: Puzzles, interivews
Now every technical interview involves a whiteboard/computer coding/solving of simple/medium level puzzles. As any sport, one needs recent practice to perform well. I did not practice in that since 1998, and I only had one such interview in ~2010 with google, where I failed.

I don't argue that it is not a worst proxy for evaluating programmer's job performance (in the same way as running speed/stamina is a proxy for evaluating football player skills).

I decided to spend some time to understand my current status and improve it a little bit. So I selected a random puzzle from hackerrank with medium rating and low average pass count.

It took me about 3 hours in total to come up with a correct O square algorithm, and one hour to implement.

This Clojure implementation by the way is probably not O square as it times out on bigger tests. So I need either to profile it and fix, or re-write in C where reasoning about execution time is trivial.

So if I got this puzzle at a Google/Facebook/whatever interview, I would have failed, as one needs to solve this in 30 minutes, not 4 hours. And when I encounter puzzles of similar complexity at work (not very frequently, maybe once every couple of months), solving it in 4 hours is never an issue.

Upd:
For two people, who are much brighter than me, it took several minutes to find the algorithm which is O(n) and describe in the comments. I implemented it (took me half an hour), and now it passes all hackerrank tests:
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30th July 2018

9:49am: Russian butterfly effect
9 дней/Сутин. 301062 @ flibusta.
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