Wednesday, 22 September 2010

Multicore Bottleneck

Today, while reading some materials about Parallel Programming, partitioning datasets and so on, some old echos from the past came to my mind.

In most of the simple samples that I've seen lately, a bunch of data gets loaded into memory, and then the memory dataset is partitioned and each thread reads data from one of the data partitions. We do the whole loading into memory before launching the threads because otherwise different threads would be accessing to disk simultaneously and the I/O bottleneck would keep threads stuck while the I/O operation for other thread gets completed.

OK, I've said bottleneck. There's one that's been well known since long ago, Memory bottleneck. Years ago, as CPUs got faster and faster, the memory access technology was unable to keep up, and we had the problem of a fast CPU on hold waiting for the data retrieval from memory... We have caches and branch prediction to soften the problem, but anyway, it's still there.

Since some years ago CPUs speed has barely increased, but we have several cores, and more and more cores to come... This means, that it's not only that an operation will be we waiting for the memory to provide the data it needs, it's that multiple parallel operations will be waiting for the same memory to provide those data through the same data bus that we had years ago.
This sounds messy, so I thought sure there was some work around in place for this that I was missing (it's been a long while since the times when I was a hardware freak following the last improvements in chipsets and buses...), but after some googling it doesn't seem so, and in fact we can say that Multicore makes the memory bottleneck worse.

Saturday, 18 September 2010


I was in London last week, and once again (despite having been there many times) the omnipresence of CCTV cameras in public spaces continues to astonish me.
I have mixed feelings about them, but in general, however strange this may seem to many of my friends, in this particular case positive feelings win.

I think central London (taking as central a really large area) is one of the safest places that one can find in a modern metropolis. I don't like being surveilled by the the police, the state or whoever... but if I weigh up the moral disturbance that being observed causes me against the risk of being mugged by a violent gang, finding all public toilets, phones... vandalized, etc... I'm afraid I've turned so conservative to happily accept being monitored...
Well, maybe this thought is common to many Londoners, as otherwise it would be hard to understand that a population that has so fiercely opposed to Identity Cards could accept the attack to privacity that CCTV involves.

Related to this (but with a much broader scope) Tate Modern is hosting an exhibition that seems pretty interesting:

Exposed: Vouyerism, surveillance and the camera

No doubt CCTV has been, is, and will ever be a hot, controversial topic, and street art clearly reflects it:

Banksy, Marble Arch, London, 2004:

Marble Arch, London, September 2010:

Frankfurt, August 2010:

Update 2011/06/02
When I was in Munich last April (world famous for its impressive Bavarian baroque architecture, but its less known Art Nouveau treasures are also stunning) I came across this good addition to this post:

I think it reads something like: "Dictatorship of Safety"

Wednesday, 8 September 2010

Some good films

I've seen some rather good films lately, but I don't feel like writing a full entry for each of them (as I've said before my knowledge about cinema is rather limited, I rarely watch old films, I'm much more into stories than into interpretations...).
So here's a listing of a few good films to spend your time with:

  • WAZ. Great horror/thriller film. It's been compared to Saw and Seven in most reviews, and I agree with it, but would like to point that it's not that bloody as the last Saw installments, there's blood and "cruelty", but these are absolutely necessary. A well thought story about catharsis through revenge, about destroying those who destroyed you, using the same weapons. Same as with Amanda in Saw, I seem to love this kind of vindictive women.

  • Before the Devil knows you're dead. Very good story about 2 brothers trying to save their spoiled lives by robing their parent's jeweler's. The great plan ends up being a total disaster, and the consequences are even worst. I like how it depicts the decadent lives of 2 men and how they sink more and more.

  • In Dreams, pretty good and not much known terror film. Revolves around the pain of a woman whose only child has been murdered by a serial killer. The woman has terrible nightmares about the new crimes to come and is about to get nuts. Intense film where you almost taste the suffering of the main character.

  • Desert Flower. Based on a true story about a Somali woman that has suffered female genital cutting, I was expecting a harsher experience, but anyway it's an entertaining film and a good story. It's strange to see how something I reject so much as it's the fashion industry (I see it as a clear example of how banal and lacking in interests our Western Society has turned) in this case manages to fix the life of someone (in a sense a victim of that same social decay).

  • Man on Fire. Another good story about broken lives, revenge and redemption. A war mercenary turned into a body guard unexpectedly finds a reason to live and to die for. The setting for the story (modern day crime ravaged Mexico) fits pretty well.

  • The burning plain. Great film writtend and directed by the screenwriter of Amores perros, 21 grams... and starring Charlize Theron. So, the credentials are great, and the film really lives up to them. An interesting story stretching over more than a decade and told in a non lineal way. Sons that repeat their parent's "sins" and painfully drown in fear, guilt and remorse end up finding redemption in love. As a plus, I can't help saying that Chalize Theron along with a great interpretation gives us great views of her body ;-)

Friday, 3 September 2010

Chernobyl wild life sanctuary

This entry is related to the one I posted last week regarding how happy the planet would feel if he managed to get ridden of that plague that we are...

Reading an article in Muy Interesante (a Spanish popular science magazine) about Chernobyl 24 years after the accident, I've found that wildlife has flourished in the place, and rare species have returned, leading the Ukrainian government to designate the area a wildlife sanctuary.
There's some controversy around this, with claims against this positive effect, but anyway:

  • on one side it remains as a really interesting research case, from which we can learn about how organisms are able to adapt to cope with high radiation levels, and how really damaging different radiation levels are to life

  • on other side, We, Humans, seem rather more damaging for other species than a Nuclear explosion and its associated radiation...

Over the years I've watched several documentaries about the Chernobyl accident and its effects, but no doubt that the best one I've watched is this, an excellent research that reveals what governments kept hidden for many years, that after the first explosion there were chances for a much worse second one to happen, one that could have wiped out from the map a good part of Europe.
I remember from another documentary (that I can't find now) how lucky we were in Asturies regarding the radiation, winds kept blowing in such a way that the main radioactive cloud did not reach us. You can see the cloud behavior on this video.