Author: Christophe Theron
Date: 19:43:28 03/27/01
Go up one level in this thread
On March 27, 2001 at 22:03:31, Robert Hyatt wrote:
>On March 27, 2001 at 18:12:42, Christophe Theron wrote:
>
>>On March 27, 2001 at 14:08:03, Robert Hyatt wrote:
>>
>>>On March 27, 2001 at 12:55:10, Christophe Theron wrote:
>>>
>>>>
>>>>
>>>>That's right.
>>>>
>>>>Actually as the title says, the message is directed to people who are
>>>>considering to buy a dual.
>>>>
>>>>As far as I know quads are so expensive that it would be ridiculous to buy one
>>>>just to play chess.
>>>>
>>>>
>>>>
>>>
>>>
>>>
>>>At the moment, perhaps. 6 years ago duals were just as expensive. Now they
>>>are dirt cheap. As quads become more common, their prices will continue to
>>>drop. 5 years ago a quad MB for pentium pro 200s would set you back almost
>>>$8,000. Today you can buy an Intel SC450NX for 2500 bucks, that includes
>>>three hot-swappable 400 wat power supplies, motherboard, 6-slot hot-swap raid
>>>disk cage, 3 on-board scsi controllers, 1 on-board video controller, etc.
>>>
>>>All you lack is cpus, memory and drives.
>>>
>>>That is a huge reduction. The curve is going downward each year. Now the
>>>quads are slowly reaching reasonable price points while the 8-way boxes are
>>>way expensive. In 5 years that too will change I'll bet...
>>
>>
>>
>>So I would advice people who are considering buying a dual right now to delay
>>their buy by several years...
>
>Using that logic you should advise everyone to _never_ buy a computer, because
>next year will _always_ have a faster processor.
No, it's not the same logic.
You are saying that "the curve is going downward each year", which means that
the price difference between a single processor machine and a dual is smaller
every year.
Based on this remark, it is clear that what you get for your money on a dual
will at some point be better than what you get for a single.
This is not dependant to the typical speed at that moment in time. It's not the
same as saying "wait for next year, you'll get a faster computer".
It's like saying "a dual right now is not worth it when you compare to what you
get with a single, but wait because soon it will be".
>>>>You are always thinking with unlimited resources in mind!
>>>>
>>>>I don't disagree with you here, but in real life there are people wondering if
>>>>it's worth it to buy a dual.
>>>>
>>>>And depending on how much money they can put on it, they will have to choose
>>>>between a single 1.GHz and a dual 1GHz.
>>>
>>>OK... but there the dual will perform like a 1.7ghz machine. Which will
>>>turn into around 60 rating points improvement. That is not trivially
>>>ignorable.
>>>
>>>Each time I teach a parallel programming course here, I will find around one
>>>out of every 10 students has a dual-processor machine already. And when I ask
>>>what they paid, they generally say 500-1000 US bucks...
>>
>>
>>
>>In the place I live, I cannot even buy a dual. I must order it overseas.
>>
>>Bob, there are people outside the United State of America, you know.
>
>
>I ordered mine. There is no "local store" that sells quads here. You can
>go to any local computer store and find a dual however... Gateway even sells
>them at the local outlet..
What you can get where you live has nothing to do with what I can where I live.
>>You are very lucky to live in a place where you can get all kind of high tech
>>stuffs for a fraction of your monthly salary, but in other countries a dual
>>represents a huge amount of money.
>
>A dual represents 500 bucks for 2x800 or so. I don't know what the exchange
>rate is, but that can't be huge...
Where I live you need much more money to buy a dual.
>>For example, a dual represents more than my average monthly salary.
>
>
>You _really_ make less than $500 US dollars per month?
No, it's just that a dual here costs much more than $500.
Sometimes I wonder if you have ever travelled outside USA...
>>>>If you can afford to buy a dual 1.2GHz, then you just stop after reading the
>>>>first paragraph.
>>>>
>>>>If not, then I think the rest is worth reading...
>>>>
>>>>
>>>>
>>>>
>>>>>That is flawed. For multiple reasons. The shared hash table holds _most_ EGTB
>>>>>results after a single probe. The EGTB cache is threaded and shares data read
>>>>>between the two (or more threads). With the compression scheme Eugene uses,
>>>>>the reads are kept to a minimum. I have run extensive tests on my quad with
>>>>>one single 9-gig SCSI drive servicing 4 threads for EGTB reads. I don't see
>>>>>any severe strangulation due to disk backlogs. most threads are searching
>>>>>close enough to each other in the tree that they are probing the _same_
>>>>>tablebases. The caching Eugene wrote handles this quite well.
>>>>
>>>>
>>>>
>>>>OK, I admit that I have not done any test on this issue, so your input is
>>>>appreciated.
>>>>
>>>>If my figures are wrong I will publish an update for this text.
>>>>
>>>>Do you have any measure of the slowdown expected when 2 thread are accesing
>>>>intensively the same EGTB files? That would help us to compute the corresponding
>>>>ELO loss.
>>>
>>>I generally don't notice any degradation at all. Mainly because of the large
>>>well-managed cache buffers, no doubt. But then the operating system also does
>>>a lot of file caching on top of what Eugene does, and all of this (on a 512mb
>>>machine) goes a long way toward controlling "disk buzz".
>>
>>
>>
>>Well on my computer when I set up an endgame position I have my hard disk
>>working really hard.
>>
>>I can hardly see how this poor hard disk could manage to serve two threads
>>instead of one without some performance penalty.
>
>
>First, the two threads are searching positions that are similar, so they will
>both probe the same tables for the most part. And since the probe code uses
>a shared cache for both threads, many reads are eliminated. And once a
>position is probed, it sticks in the hash table from that point forward
>anyway...
>
>I typically see very little slowdown when reaching 8-10 pieces on the board.
>In a few rare cases, it does slow way down but it isn't very common with the
>way I implemented the probe...
>
>
>
>
>>
>>On the other hand, if you need to have a high perf SCSI drive to satisfy the
>>needs of the dual, and such an amount of memory, this has to be added to the
>>invoice.
>
>SCSI and EIDE are not too far apart. Typically a couple of hundred bucks
>added for the same size. And EIDE is not horrible for database probes. I
>run on such machines all the time and don't see any serious performance
>problem when compared to SCSI.
And what is a couple of hundred bucks... Nothing. Can't even get a meal for
that... :)
>>Remember that all this is about what you get for the money, what you need really
>>and is it worth it.
>
>Almost all new PCs have 256mb of RAM. 128mb DIMMS are selling for 50 bucks
>nowadays, so going to 512mb adds $100 to the price of the machine. And the
>machines I use are pretty much all 512mb boxes... This seems to work
>acceptably.
Again: the prices in the US have nothing to do with the prices OUTSIDE.
>>>>I did not try to cover quads in the message because I don't think many people
>>>>could afford to buy one.
>>>>
>>>
>>>I realize that. But 5 years ago you wouldn't have found anyond considering
>>>buying a dual either. Quads will eventually reach the same pricing level,
>>>based on a curve over the last 5 years..
>>
>>
>>
>>People, wait for 5 years before you buy a SMP machine.
>
>Don't buy that 1.5ghz machine this year either. Wait for next year's 2.5ghz
>processors. But wait, don't buy that either as the next year we will be at
>4.0 ghz. But why waste the money on that machine when the next year will see
>5+ghz processors?
That's not the reason why I said it was better to wait, and you know it.
>As Eugene said, based on _lots_ of experience, I would _much_ prefer a dual
>800 to a single 1.2ghz machine. It responds better. It handles two compute-
>bound processes _far_ better due to less cache thrashing. And it will be
>cheaper to boot.
And it will warm your room up. :)
>>>>So far I have seen a number of people on CCC asking for duals, but nobody ever
>>>>said he was considering to buy a quad.
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>>>A difference in ELO points in real life turns into a winning percentage.
>>>>>>That's exactly what ELO means, and how it is computed.
>>>>>>
>>>>>>For winning percentages above 20% and under 80%, there is an approximated
>>>>>>formula that works pretty well:
>>>>>>
>>>>>> ELOdiff = ( WinPercentage - 50 ) * 7
>>>>>>
>>>>>>From this you can deduce how to compute WinPercentage if you have the ELOdiff:
>>>>>>
>>>>>> WinPercentage = ELOdiff / 7 + 50
>>>>>>
>>>>>>If ELOdiff=25, then WinPercentage = 53.57% (we are between 20% and 80%
>>>>>>so our above formula applies).
>>>>>>
>>>>>>So we are talking about a difference of 3.5 games each time you play 100.
>>>>>>
>>>>>>
>>>>>>****************************************************************************
>>>>>>** When you play 100 games with your dual 1GHz against **
>>>>>>** your single 1.2GHz, you can expect the dual to win typically **
>>>>>>** by a 3.5 games margin. **
>>>>>>****************************************************************************
>>>>>
>>>>>
>>>>>I would change that to
>>>>>
>>>>>winpct=60/7+50 which is about 60%. Out of 100 games that turns into winning
>>>>>60 and losing 40. BTW in your above comment you need to double that 3.5. If
>>>>>I win 53.5 games out of 100, you win 46.5. The _difference_ is 7 games. Not
>>>>>3.5
>>>>
>>>>
>>>>When you win a game, your opponent loses it. I don't count this as 2 games.
>>>>
>>>>
>>>>
>>>>
>>>
>>>Then maybe your term wasn't clear to me instead. You said "I win 53.5% of
>>>the games. Out of 100 games that is a difference of 3.5 games." If I win
>>>53.5% of the games, you win 46.5% of the games. That is a bit different
>>>since our scores are separated by 7, not 3.5...
>>
>>
>>
>>OK, OK. I don't want to split hairs.
>>
>>What counts is the difference between the winning percentage and 50%. Because it
>>is what you multiply by 7 to get an estimate of the ELO difference.
>>
>>If I run a match with even hardware, I win 50 out of 100 games.
>>
>>If I run a match with a dual I win 53.5 out of 100 games.
>>
>>With my dual I win 3.5 more games. OK?
>>
>>
>>
>> Christophe
>
>
>OK. but I will bet that you win more than 3.5 more games. Because the
>actual performance gain is still in the 1.7X range overall, maybe better in
>a full game (I get 1.7X over large problem sets. chess programs do better in
>a game as they typically search deeper due to pondering.
It's more than 3.5 games if you buy a dual system with the FASTEST processors
you can find. If it is not affordable and you end up with a dual that is just
20% slower than the fastest single processor computer you could have bought,
then it will be 3.5 games.
Christophe
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