Bugz

Jul. 11th, 2017 12:20 pm
izard: (Default)
The worst kind of bugs - 3rd party libs dependencies..
On a fresh Fedora 26 install on one of my test servers, one of the tools I needed wanted to install some gtk and gdk dev libs.
# yum install ...
"you are about to install a ton of deps, tolal 100Mb" Y/n
Y
"done"
A tool works.
Now I need to install a kernel src package:
# yum install ...
File "/bin/yum", line 57, in
from dnf.yum import main
...
ImportError: /usr/lib64/python3.6/site-packages/rpm/_rpm.cpython-36m-x86_64-linux-gnu.so: undefined symbol: PySlice_AdjustIndices
Previous installs broke yum!

Very cool: I can't even google PySlice_AdjustIndices, and PySlice library simply does not have AdjustIndice method in 3.6.0, only SetIndices...

Of course I don't care to debug deeper (or file bugs with Fedora), it is just easier to re-install.
izard: (Default)
I have to admit that I was wrong - when I first read about roofline model several years ago I thought it is too abstract to be used in a real s/w performance work.

It is not, and Intel Advisor tool that visualizes loops in roofline model actually more makes sense than I thought.
izard: (Default)
- Пусть мама сродит мне братика!
- Почему не сестренку?
- Девочки лучше, но с ними сложнее, а у мамы сил нет.
- А с братиком придется делиться ресурсами?
- Игрушками? Я старше, так что он у меня отнять не сможет, а я у него смогу. Но я своими буду делиться, иногда, ненадолго. А ему ты будешь тоже игрушки покупать, а я у него брать.
izard: (Default)
Yesterday Akhilesh Kumar, the Skylake-SP CPU architect announced mesh architecture for future Xeon CPU,

that replaces ring. The ring was there in Xeon for 6 generations, and once the server CPU has grown from 4 to 20+ cores, latency of the ring became an important factor to consider in software performance work. In last 4 architectures, there were even sub-rings (Cluster-on-Die) to address this. Some folks were reverse-engineering a secret (though simple) hash function that directed different cache lines to different chunks of last level cache.

No need any more. That is just one of great features in the upcoming CPU.

The circle

Jun. 5th, 2017 02:03 pm
izard: (Default)
After [profile] blau_krahe suggestion, I just read it during this long weekend. The narrative style in Russian is very similar to "Холодная зона" by the way.

It is fun to read, but unlike "Холодная зона", everything in this book seems just trivial. First 20% or so is absolutely realistic, then as the plot becomes somewhat darker in the following 10% of the book, the rest 70% becomes obvious. So I guessed all the remaining plot after I read the first 30%, just thinking: "What would an american author write to make absurdity grow until a possible maximum is reached." I think if the author would have been european, it would not be that easy.

So in a hindsight, I would recommend reading the first 30% of this book, skipping all the rest but last 5 pages or so.

Aphids

Jun. 4th, 2017 09:08 am
izard: (Default)
Ants can't reach young leaves of a beech next to our home, so all the sugar aphids produce just crystallises on leaves.

Very tasty :)
izard: (Default)
I got a weird problem with a neighbour, that demonstrates a typical German way of communication. My wife needed some room in a trunk of our car for shopping, so she removed a folding stroller from the trunk, and left it at our parking lot. (The parking place at our building's underground parking that belongs to us). In couple of hours Yulia came back, and did not find a stroller. She looked around and found it ~20 meters away, at some other neighbor's parking lot.

In the evening, I found a letter (with date, name and signature) under my car's wiper:

"Hi, I accidentally rolled over a stroller that was lying at your parking lot. Now I have some scratches on my car, if the stroller belongs to you, please call me +49NNN to discuss the compensation."

I wonder what I do next, obviously my German is not good enough to discuss these matters over phone, and Yulia would not stay calm during the conversation (though even if it turns out to be our fault, we still have an insurance for that).

I am also very curious, what would happen in US and Russia in the same circumstances?

work stuff

May. 22nd, 2017 04:19 pm
izard: (Default)
1. Looks like openvswitch constantly monitors PMUs, so it is difficult to monitor it's performance externally :(
2. I was asked to explain why sharing workload to 2 cores with 80% utilization was equivalent to sharing it to 6 cores with 40% utilization. Kinda funny, shouldn't it be obvious?
izard: (Default)
2 years 11 months old, riding on my neck:
- Я всадник! Я - полицейская конная стюардесса!
(перечислил все любимые профессии)
izard: (Default)
As a backer of few dozens of kickstarter projects (that is the only way of shopping that I like), I noticed a pattern..

Many projects that I backed were very similar:

There is a product/gadget/tool (I'll call it bells and whistles, or B&W for short). One can buy B&W at one dollar shop for 10$, made in China, and the quality will be awful. You could probably use it once or even less, and it will break. In a supermarket, B&W will cost 50$, and you may use it 1-20 times before it breaks, if you are careful enough. Sometimes there is a high end variation available online, you may buy it for 100$, and it will last almost forever in non-professional use. Very often there is also a luxury/professional version that costs 500$, which is perfect but too expensive for an occasional user.

All above is likely manufactured in China, with BOMs of 1$, 10$, 20$ and 80$ respectively. Retail, marketing, brand/revenue combined makes up the rest of the price.

So at kickstarter, there are plenty of successful campaigns that have many nice words about R&D, but in fact it is just a procurement of B&W from a Chinise manufacturer at $60 BOM, selling it for 120$. For the end user, B&W from kickstarter at 120$ is often as good as a professional thing for 500$.

I guess this pattern is not fulfilling original kickstarter's mission to fund new R&D, but that is how it is.
izard: (Default)
Russian popadancy/althistory that does not suck. 1933-1937, 0% technical progress, nobody warns "tovarisch Koba et al". Group of "popadancy" just try to make WW2 into a series of smaller scale conflicts by clever espionage plots.

O(n^3)!

Apr. 20th, 2017 09:59 am
izard: (Default)
Here is the code for the previous post

I should have wrote this code in the first place, took me only 5 minutes anyway. [personal profile] spamsink was right: apparently in runs in slightly below O(n^2).

But my proof of O(n^3) still stands, and I found a German university computer science textbook that also proves it should be O(n^3) in the worst case... Riddles!
izard: (Default)
Those interview questions... I am not fond of computer science riddles, but some are.

I am reasoning about Welzel's algorithm complexity:
(to find a minimal bounding circle over set of points P, there is a recursive algorithm:
circle mbcr(P[n], R)
if |P| = 0 or |R| = 3
return get_circle(R)
if (P[0] in mbcr(P-P[0], R))
return mbcr(P-P[0], R)
return mbcr(P-P[0], R+P[0])

In a textbook, they say complexity is ϴ(n) for average case and O(n^2) in worst case..

I am getting different values. Lets assume worst case, when "if (P[0] in mbcr(P-P[0], R))" is always false.
mbcr(n, |R|=3) = O(1) - obviously.
mbcr(n, |R|=2) = O(n) - n * first recursion point, and each time it gets only once to second recursion point (which is mbcr(n, |R|=3) case).
mbcr(n, |R|=1) = O(n^2) - T(mbcr(n, |R|=1)) = O(n) + (n-1) * T(n-1, |R|=2)) = O(n + n^2) = O(n^2)
mbcr(n) = O(n^3) - T(mbcr(n)) = O(n) + (n-1) * (T(mbcr(n-1,|R|=1)) = O(n) + O(n^3) = O(n^3)

What am I missing?? Everything above seems very clear for me, can't stop thinking about this simple problem.

on new GitS

Apr. 3rd, 2017 12:41 pm
izard: (Default)
Watched it yesterday, and I like it more than original.

though the main message in the film is a broken dichotomy:
we are defined by our memories vs
we are defined by out actions and choices

Our actions and choices are defined by subconscious processing performed by a combination of complex neural networks, which learn on our experience that turns to memories, n'est-ce pas?
izard: (Default)
I can share some personal statistics on these 3 airlines I use the most in last ~10 years.

It is about economy, I never flown business with Aeroflot or Turkish.
10 years ago:
Food: 1. LH, 2. Turkish, 3. Aeroflot
Service: 1. LH, 2. Turkish, 3. Aeroflot
5 years ago:
Food: 1. Turkish, 2. Aeroflot, 3. LH
Service: 1. LH, 2. Turkish, 3. Aeroflot
now:
Food: 1. Aeroflot, 2. Turkish, LH (Still big plus for Turkish - they have Ayran!)
Service: 1. LH, 2. Aeroflot, 3. Turkish

Its a pity Turkish airline's food is now just good, not fabulous as it was just a few years ago..
izard: (Default)
I think today was the first time I seen this message in a terminal:
# ssh $IP
do_ypcall: clnt_cal: RPC: Time out
You don't exist, go away!
#

Good sense of humor, guys!
izard: (Default)
In November, I went to German immigration authorities with a question.
- Hi, how can I do X?
- You should collect a pile of documents (here is the list, it could take couple of months), then once your documents are all OK you schedule an appointment with us.
- Can I schedule an appointment now and then make my documents?
- No, you should have all documents ready.
4 months later, I got all documents ready.
- May I schedule an appointment, I got all my documents ready.
- Sure, the next available date is December 2017.
- But some of my documents will expire till then! These appointments used to take 2 weeks to schedule two years ago!
- Right, you'll need to get these documents again. Now we have so much work with refugees, so the appointment lead time is now at least 8 months..

Some fish

Mar. 22nd, 2017 11:32 am
izard: (Default)
Most of the corals are dead, but there is still some life.

Mooray eels, turtles, snorkelers, big groupers:
Read more... )
Full album link.
izard: (Default)
Of course, I could not make it without a computer. But I did not want to use a laptop or smartphone, so I took this device.

It is an Intel compute stick, and first I thought it is pretty useless, so I did not buy it when it came out. But then I won it in a draw, and found a good use: every hotel room I stay in has a big screen digital TV that I never switched on until now. The device is powerful enough to run heavy photo processing software, so I edited my pics in the evenings.

How it helped internet detox? During one week, I did not read LJ friend feed, only checked facebook once, only checked work email twice, read only 5 articles on habrahabr, and read only about 10 pages of junk books. That is less than 5% of traffic I typically consume, so I feel almost sober now :)
izard: (Default)
Until March 22nd, I will be staying in a rehab for internet junkies. Obviously, there is no internet there (maybe I'll find a way to read my work email every couple of days :)

If there is anything I should know, write me now or please remind me in two weeks.
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