Author: Vincent Diepeveen
Date: 06:19:47 02/25/03
Go up one level in this thread
On February 25, 2003 at 08:56:27, Robert Hyatt wrote: Bob it is 10ms latency. period. >On February 25, 2003 at 07:44:23, Vincent Diepeveen wrote: > >>On February 23, 2003 at 01:38:55, Matt Taylor wrote: >> >>DIEP is spinning and locking way way less than Crafty. Note that >>it is pretty hard to do without spinning under linux. > >1. It is not "hard to do" under linux. Default pthread_lock() doesn't spin, >the >process blocks. But that is inefficient if the lock is only held for a few >instructions. > >2. My lock overhead is not very significant. From actual measurements rather >than guesswork. > >> >>The runqueue fires at 100Hz in linux. So the latency for a thread that doesn't >>search and normally is doing all kind of stuff is around 10ms under linux. > >That is wrong. the run-queue "fires" whenever a process releases a lock that >another >process is waiting on, if there is an idle processor. > >> >>For crafty 10ms latency is too much to wait for a thread to get fired for sure. > > >Yes, but there is no 10ms latency. > >> >>I guess you didn't try to figure out what the cost of it is, otherwise you would >>not write such unprofessional comments like below. > > >Right. I guess you haven't tested _anything_ or you wouldn't write such >nonsense >as above??? > > >> >>In DIEP under linux i do not idle either. Of course for me 10ms is too expensive >>too. Instead i generate a bunch of attacktables instead an idle process doesn't >>hammer at the same cache line like crafty does. > >hammering the same cache line is _very_ efficient, sorry, that is the point for >a >"shadow lock" in fact. > > > > >> >>It speeds DIEP up 20% (in nodes a second) at 32 processors when i do not take >>the 10ms penalty but go for doing something with the registers without hurting >>shared cache lines (so just local allocated stuff). > >There is no 10ms penalty in linux, so I have absolutely no idea what you are >talking about. If there is an idle processor unblocks, that processor starts to >work _immediately_ not after 10ms. Where you got that I have no idea. > > >> >>Under windows the runqueue fires at 500Hz, so that's 2ms latency. Still a lot, >>but a lot less than 10ms latency. Today i go test what the effect of that is for >>DIEP. I have no dual Xeon to my avail at the moment to test it though. Must do >>with a dual K7 and dual P3 and see what generating 600 attacktables (about 0.5 >>ms at the dual k7) just in local ram is going to give versus using >>WaitForSingleObject. >> >>So for processes that let threads idle instead of letting them spin, that is a >>complete pathetic idea for realtime environments. > > >And of course you didn't answer the question: "did you modify your spinlocks >and spinwaits" to use the pause instruction so that hyper-threading works >efficiently when one of the two logical cpus is spinning?" > >I know it is "unprofessional" to ask a technically precise question that is >important >to the thread being discussed. But I guess I couldn't help myself. After all I >thought >that there should be _some_ technical merit in a thread you post in. > >The spinwait/spinlock problem is well-known. It's been discussed in a paper on >the >Intel web site. All you had to do was read it, or follow the discussions here, >or look at >my spinlock code, to see what the problem is, and how to fix it... > > > >> >>>On February 23, 2003 at 00:39:34, Robert Hyatt wrote: >>> >>>>On February 22, 2003 at 02:54:21, Vincent Diepeveen wrote: >>>> >>>>>On February 21, 2003 at 19:49:04, David Weber wrote: >>>>> >>>>>>what chess programs support hyper-threading >>>>> >>>>>DIEP, Crafty, Fritz. >>>>> >>>>>for fritz it speeds up 10% node count at 4 threads at a dual Xeon 2.8Ghz >>>>>(compared to HT turned off and 2 threads), but chessbase didn't test yet whether >>>>>it actually speeds up search depth (according to Mathias who operates fritz >>>>>here). >>>>>for shredder it does speed up the node counts but not search depth >>>>>so it has SMT/HT turned off here at this tournament and runs with 2 threads at a >>>>>dual Xeon 2.8Ghz here. >>>> >>>> >>>>Did you make the necessary changes to spinlocks and spinwaits??? >>> >>>Sorry, can't resist a good laugh! >>> >>>"No, they're not out yet!" >>> >>>:-) >>> >>>-Matt
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