Author: Eugene Nalimov
Date: 10:58:06 11/01/02
Go up one level in this thread
I cannot produce the test you are demanding, as I don't have physical access to the system on which I run the test, but here are my results. Dual P4/2.4GHz, hyperthreating turned on, Windows XP Professional. Unmodified Crafty 19.0 (i.e. with "bad" spinlock loop). "Bench" results (executable restarted after each test). mt=1: 976knps, 57 seconds mt=2: 1,705knps, 38 seconds mt=4: 2,006knps, 35 seconds I.e. there is not only ~17% raw nps speedup, but *absolute time* is also ~8% smaller. And that is for the executable that is non-hyperthread aware, i.e. contains bad spinlock loop. I tested exactly the executable that is on Bob's FTP site. You can download it yourself. Thanks, Eugene On November 01, 2002 at 13:06:53, Vincent Diepeveen wrote: >On November 01, 2002 at 12:20:14, Robert Hyatt wrote: > >Feel free to ship a version of crafty that doesn't do spinlock >or whatever you want to modify. I'll extensively test it for you >at all P4s i can get my hands on... > >I would be really amazed if you get even 0.1% faster in nodes a >second... > >...of course it must be a fair compare in contradiction to what >intel shows. They do next comparision > > a) some feature called 'SMT' in the bios turned on > - just running 2 threads then > b) turning it off > - also running 2 threads at it > >Like everyone who is not so naive we know that you also need >to do next test: > > a) some feature called 'SMT' in the bios turned on > - just running 1 thread eating all system time > b) turning it off > - also running 1 thread eating all system time > >There shouldn't be a speed difference between a and b of course. > >That verification step is missing. > > > >>On November 01, 2002 at 11:56:56, Vincent Diepeveen wrote: >> >>>On November 01, 2002 at 10:41:25, Robert Hyatt wrote: >>> >>>>On October 31, 2002 at 10:53:07, Vincent Diepeveen wrote: >>>> >>>>>On October 30, 2002 at 06:59:21, Terje Vagle wrote: >>>>> >>>>>>Hi all, >>>>>> >>>>>>The new cpu from intel will have a new function called >>>>>>hyper-threading. >>>>>> >>>>>>This will make the operating system able to recognize the cpu as if it was >>>>>>2 cpu's. >>>>>> >>>>>>Could the programs with smp-support make use of this? >>>>>> >>>>>>Regards, >>>>>> >>>>>>Terje Vagle >>>>> >>>>>No chessprograms cannot make use of that feature at all. It is sad but >>>>>the truth. Hyperthreading is a cool thing for the future but the P4 >>>>>processor is a too small processor to allow hyperthreading from getting >>>>>to work. >>>>> >>>>>Apart from that a major problem is that even if we have a great processor >>>>>which really allows hyperthreading to be effective, that the threads >>>>>run at unequal speeds. >>>>> >>>>>Hyper threading is supposed to work for 2 threads where 1 is a fast >>>>>thread and the other is some kind of background thread eating little cpu >>>>>time. >>>>> >>>>>In chessprograms having a second search thread which just runs now and >>>>>then in the background is simply impossible to use. >>>> >>>> >>>>It is not impossible at all. The only problem was spinlocks and Eugene >>>>posted a link to an Intel document that describes how to solve this problem. >>>> >>>>Given that solution, hyper-threading will work just fine since spinlocks >>>>won't confuse the processor... >>>> >>>>It won't be 2x faster, but it will certainly be faster if you can run a second >>>>thread while the first is blocked on a memory access... >>> >>>No it won't be 2 times faster. suppose you start crafty with 2 threads. >> >>I didn't say it would be _two_ times faster. >> >>I said it would be _faster_. >> >>And it will. >> >> >> >>> >>>thread A starts search and has 1.e4,e5 >>>thread B starts and continues with 1.d4 >>> >>>now when A is ready, B will still be busy with its own search space, >>>and delay thread A time and again. >>> >>>that'll slow down incredible. >>> >> >> >>Except that isn't how it works. The threads co-execute in an intermingled >>way as one blocks for a memory read the other fills in the gap. It is >>something like having 1.5 cpus... and it does work. >> >> >> >>>You'll be a lot slower than searching with a single thread! >>> >> >> >>Not very likely... >> >> >> >> >>>Also note that there is just 8 KB data cache and just like >>>40 registers to rename variables. then another 12KB tracecache. >>> >>>*both* threads are eating from that 8 KB and 12KB tracecache, >>>that is an additional problem they 'overlook'. >>> >> >> >>That is a problem on an SMP machine. But _both_ threads are executing >>the _same_ code anyway... so that isn't a problem. At least for me. >> >>For you it is different because you are not using "shared everything" in >>lightweight threads, so your results might be different. But all my threads >>share the exact same executable instruction code... >> >> >> >> >>>As you can see from graphs. Usually SMT brings zero speedup. >> >>I have seen numbers around 1.3 up to 1.5... which is not to be >>ignored. >> >> >> >>> >>>Try crafty on a 2.4Ghz single cpu P4 or P4-Xeon please (northwood) or >>>above. Not on a slower P4 or P4-Xeon. Of course we go for the latest >>>hardware... >> >> >>Why does it matter? Hyper-Threading is Hyper-Threading, unless you are >>going to start that memory speed nonsense. And, in fact, the faster the >>processor vs memory speed, the better hyperthreading should perform. Just >>like the greater the difference in processor speed vs disk speed, the better >>normal operating systems do at running multiple processes. >> >> >>> >>>Just try it like i tried at Jan Louwman's 2.4Ghz P4s and 2.53Ghz P4s. >> >>That says it all. "Like I tried it". As if that is a comprehensive and >>exhaustive testing? >> >>> >>>I can't measure *any* speedup *anyhow*. >>> >> >> >>Why am I not surprised??? >> >> >> >>>Also theoreticlaly i see major problems for the P4 chip even if you >>>have software which could theoretically profit. >> >> >>"theoretically". >> >>:) >> >>:) >> >>:) >> >>Theory from someone that doesn't know theory. >> >>:) >> >>:)
This page took 0.01 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.