Author: Robert Hyatt
Date: 14:43:12 04/14/03
Go up one level in this thread
On April 14, 2003 at 17:15:41, Vincent Diepeveen wrote: >On April 13, 2003 at 22:39:39, Robert Hyatt wrote: > >>On April 13, 2003 at 11:49:28, Vincent Diepeveen wrote: >> >>>On April 13, 2003 at 11:27:53, Robert Hyatt wrote: >>> >>>I said initially. It drops back to 10 splits a second in DIEP after a while. >>>Search depth matters. >>> >>>Let's compare 2 things. >>> >>> time=45.98 cpu=464% mat=0 n=37870294 fh=88% nps=823k >>> ext-> chk=638414 cap=249442 pp=9588 1rep=32966 mate=223 >>> predicted=0 nodes=37870294 evals=14565859 >>> endgame tablebase-> probes done=0 successful=0 >>> hashing-> trans/ref=28% pawn=93% used=28% >>> SMP-> split=431 stop=57 data=6/64 cpu=3:33 elap=45.98 >>> >>>MT 2 crafty 18.10 which i have here. 431 splits at 45 seconds. I guess you must >>>limit in crafty the number of splits a lot as splitting is expensive in crafty >>>when compared to the costs of a single node. >> >>I'm not sure how expensive it is compared to a node. I'll run a test where >>I do the split overhead at every node to compare, however... >> >> >> >>I don't limit them at all. The only limit is the YBW algorithm. But I split >>at the root also, which reduces them signficantly... > >I can split at the root nowadays, but i have turned it off for diep. it gives >too poor speedup for me. The interesting thing which searching SMP can give is >transpositions at a big depth which possibly are overwritten by a sequential >search. i don't want to miss them. Maybe you don't split at the root correctly. I limit this with some intelligent guesswork, so that if it appears that I might change my mind this iteration, then I don't split at the root until I have searched all moves that I think might replace the best move... > >As i showed half a year ago the chance is a bigger with SMP 2 threads/processes >that the chance that a transposition cutoff occurs with a depthleft a slighly >bit bigger on average than when doing deep sequential searches (of course >hashtable needs to be able to get filled quite some, but under practical >tournament conditions this is the case in most programs). > >I will however again experiment with splitting in root with a 128 processor run, >when this works very well. Not to reduce number of splits so much but to get the >cpu's sooner non-idling (where idling as we know is not really idling at all). > >128 cpu runs of 10 minutes are not too expensive. 1280 minutes / 60 = 21 cpu >hour. Of course the only hard thing is when you are unlucky with a run (each run >can be different and perhaps one time you have a very poor run which gives a bad >speedup, where reality is it would give a better speedup). > >Anyway splitting in root doesn't work for me with 2-16 cpu's. As I said, you have to think about it. There are ways to make it work, and it lowers overhead drastically when it is done correctly. (search overhead goes down). > >Best regards, >Vincent > >> >>> >>>Let's ignore the cpu=464% i do not understand why it says that. I have it at >>>mt=2. probably small i/o bug. >>> >>>Now let's diep search for around this time: >>> >>>Took 0.12 seconds to start all 1 other processes out of 2 >>>00:00 21 0k 0 0 21 (2) 2 (0,0) -0.022 Ng1-f3 d7-d5 >>>++ d2-d4 procnr=0 terug=1 org=[-22;-21] newwindow=[-22;520000] >>>00:00 71 0k 0 0 71 (2) 2 (0,0) 0.001 d2-d4 d7-d5 >>>00:00 175 0k 0 0 175 (2) 3 (0,2) 0.157 d2-d4 d7-d5 Ng1-f3 >>>00:00 443 0k 0 0 443 (2) 4 (0,5) 0.001 d2-d4 d7-d5 Ng1-f3 Ng8-f6 >>>00:00 150800 151k 0 0 1508 (2) 5 (0,19) 0.190 d2-d4 d7-d5 Ng1-f3 Ng8-f6 Nb1-c3 >>>00:00 318900 319k 0 0 3189 (2) 6 (0,27) 0.001 d2-d4 d7-d5 Ng1-f3 Ng8-f6 Nb1-c3 N >>>b8-c6 >>>00:00 149744 150k 0 0 13477 (2) 7 (3,68) 0.179 d2-d4 d7-d5 Ng1-f3 Ng8-f6 Bc1-f4 >>>Nf6-h5 Bf4-g5 >>>00:00 136110 136k 0 0 27222 (2) 8 (6,147) 0.001 d2-d4 d7-d5 Ng1-f3 Ng8-f6 Bc1-f4 >>> Nf6-h5 Bf4-g5 Nb8-c6 >>>00:01 127109 127k 0 0 205917 (2) 9 (45,502) 0.105 d2-d4 Ng8-f6 Nb1-c3 Nb8-c6 Bc1 >>>-f4 d7-d6 Ng1-f3 Bc8-f5 e2-e3 >>>00:04 127013 127k 0 0 572829 (2) 10 (76,666) 0.001 d2-d4 Ng8-f6 Nb1-c3 d7-d5 Bc1 >>>-f4 Bc8-f5 Ng1-f3 Nb8-c6 Nf3-e5 Nf6-e4 >>>00:17 152655 153k 0 0 2648566 (2) 11 (330,1980) 0.108 d2-d4 d7-d5 Ng1-f3 Nb8-c6 >>>Nb1-c3 Bc8-f5 Nf3-h4 Bf5-c8 Bc1-g5 Ng8-f6 e2-e3 >>>00:38 154041 154k 0 0 5889009 (2) 12 (743,4189) 0.008 d2-d4 d7-d5 Bc1-f4 Bc8-f5 >>>Ng1-f3 Ng8-f6 Nb1-c3 Nb8-c6 Nc3-b5 Ra8-c8 Nf3-e5 Nc6xe5 d4xe5 >>> >>>Of course if i use same conditions like crafty when to split then it will look >>>different with regards to the number of splits performed. >>> >>>Splitting in diep is very cheap. I already split >= 2 ply left searches and i >>>split quickly in current versions. >> >>I split everywhere. It is possible to limit this and I think the current >>version avoids splitting at the last 2-3 plies of the tree. I haven't tested >>this on my dual to see if the current value is correct, however... >> >> >>> The reason is that you get 500 cpu's quicker >>>busy and find bugs sooner. No doubt in future i will again optimize it to a >>>state where it will optimize search depth more at x86. If that's with many >>>splits a second at 2-4 processes, then i'll go for that. If it is with less >>>splits a second i'll go for that. >>> >>>Note that the 4189 number at 12 ply is not the number of splits only, it is the >>>total number of searches. So about 11*20 + 1 = 220 + 1 = 221 are from searching >>>the root. >>> >>>>On April 13, 2003 at 08:32:37, Vincent Diepeveen wrote: >>>> >>>>>On April 13, 2003 at 08:21:42, Vincent Diepeveen wrote: >>>>> >>>>>>On April 13, 2003 at 02:37:57, Tom Kerrigan wrote: >>>>>> >>>>>>>On April 13, 2003 at 01:04:52, Robert Hyatt wrote: >>>>>>> >>>>>>>>It _is_ pinned on SMT. The two logical processors are producing wildly >>>>>>>>imbalanced results when using threads, vs using two separate processes. It >>>>>>>>would appear to be cache-related... >>>>>>> >>>>>>>This is some sort of joke, right? You and Vincent see the same behavior, you >>>>>>>have SMT and Vincent doesn't, and somehow the problem is with SMT? >>>>>>> >>>>>>>How much of the time are your threads idle, out of curiosity? If one thread is >>>>>>>idle much more than the other, then of course that is going to skew your NPS. >>>>>>> >>>>>>>-Tom >>>>>> >>>>>>Of course both Crafty and DIEP are using YBW. I didn't checkout what bob does >>>>>>here, but in past in DIEP i used to always let process 0 let the search start. >>>>>>Nowadays that is not the case. The i/o thread picks the first process it can >>>>>>get. All search processes are completely identical. This process then is >>>>>>starting the search. That means the other CPUs idle when this process starts the >>>>>>search. >>>>> >>>>>also read that 'idle' not in litterary sense. Letting them REALLY idle with >>>>>sleep() or WaitForSingleObject, is at a REAL smp system (like dual K7) just too >>>>>expensive. Latency to wake up processors is at sick high levels. 15 ms just like >>>>>that. Imagine that because of the YBW search, you have to split initially like >>>>>50-100 times a second. 15ms is death sentence. So 'idle' cpu's are spinning >>>>>around until at a shared memory variable some flag is set. I let them do some >>>>>arithmetic function for a 100 times while 'idling'. >>>> >>>>If you do this right you won't split _that_ often. >>>> >>>> time=35.97 cpu=381% mat=-1 n=80006982 fh=92% nps=2224k >>>> ext-> chk=1487513 cap=353299 pp=32860 1rep=79236 mate=15135 >>>> predicted=3 nodes=80006982 evals=19493470 >>>> endgame tablebase-> probes done=0 successful=0 >>>> SMP-> split=1840 stop=163 data=15/64 cpu=2:17 elap=35.97 >>>> time used: 29.81 >>>> >>>> >>>>In the above from a game on ICC, in 35 seconds, I did 1800 splits total. The >>>>deeper the search the better this becomes... >>>> >>>> time=2:33 cpu=396% mat=0 n=282753699 fh=91% nps=1840k >>>> ext-> chk=3046093 cap=1083298 pp=16735 1rep=192964 mate=3400 >>>> predicted=8 nodes=282753699 evals=114936261 >>>> endgame tablebase-> probes done=0 successful=0 >>>> SMP-> split=2683 stop=424 data=15/64 cpu=10:09 elap=2:33 >>>> time used: 8.29 >>>> >>>> time=4:03 cpu=396% mat=0 n=466004128 fh=90% nps=1911k >>>> ext-> chk=3120074 cap=1773259 pp=60704 1rep=227466 mate=5595 >>>> predicted=9 nodes=466004128 evals=160300467 >>>> endgame tablebase-> probes done=0 successful=0 >>>> SMP-> split=5811 stop=950 data=18/64 cpu=16:06 elap=4:03 >>>> time used: 2:43 >>>> >>>> time=3:47 cpu=396% mat=0 n=421757405 fh=92% nps=1855k >>>> ext-> chk=3436512 cap=1222511 pp=75583 1rep=186606 mate=3165 >>>> predicted=12 nodes=421757405 evals=149496490 >>>> endgame tablebase-> probes done=0 successful=0 >>>> SMP-> split=3524 stop=337 data=17/64 cpu=15:01 elap=3:47 >>>> >>>>> >>>>>>In crafty that's also the case, but i do not know whether Bob always picks a >>>>>>certain thread as first. If so then that might explain quite something. >>>>>> >>>>>>Measuring idle time with SMT is very hard to do objective, but of course you can >>>>>>relatively check it out. Basically the problem is you do not know what the >>>>>>maximum % is that i can get out of SMT, because it is dependant upon the other >>>>>>process too.
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