Author: Robert Hyatt
Date: 21:05:02 04/15/03
Go up one level in this thread
On April 15, 2003 at 08:56:54, Vincent Diepeveen wrote: >On April 14, 2003 at 17:43:12, Robert Hyatt wrote: > >>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... > >i don't have a bug there. With just 2 or 4 cpu's you can split at so many points >that i chose to not split at the root. It gives a bad speedup. Not near 2.0 to >be precise. Sorry, but that is wrong. The root is the _perfect_ place to split to avoid search overhead, because we _know_ that every root move must be searched, while we can't say that with 100% accuracy about any _other_ position in the tree... See Knuth/Moore, "An analysis of alpha/beta pruning" > >However if splitting is as expensive as it is in crafty i can very well >understand you do it. It's not done because it is too expensive to not split at the root. It is done (by me) because it is more _efficient_ to do so... The math is simple. > >> >>> >>>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). > >i have it to work, it just doesn't give a very good speedup at all, that's why i >do not do it. > >Right now there is a simple extra 'if' condition > > if( .. && realply > 1 .. > >If i kick it out then it splits at the root. > That's not good enough, as I said.. There is _more_ to consider when making the decision... > > >>> >>>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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