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Memory speed testing 2+ messages / 1 participants [nested] [flat]
* Memory speed testing @ 2010-09-21 04:20 Greg Smith <greg@2ndquadrant.com> 2010-09-27 16:53 ` Re: Memory speed testing Greg Smith <greg@2ndquadrant.com> 0 siblings, 1 reply; 2+ messages in thread From: Greg Smith @ 2010-09-21 04:20 UTC (permalink / raw) To: pgsql-performance While everybody else was talking about a new software release or something today, I was busy finally nailing down something elusive that pops up on this list regularly. A few weeks ago we just had a thread named "Performance on new 64bit server compared to my 32bit desktop" discussing how memory speed and number of active cores at a time are related. This is always interesting to PostgreSQL performance in particular, because any one query can only execute on a core at a time. If your workload tends toward small numbers of long queries, the ability of your server to handle high memory bandwidth with lots of cores doesn't matter as much as access a single core can marshall. The main program used for determine peak memory bandwidth is STREAM, available at http://www.cs.virginia.edu/stream/ The thing I never see anybody doing is running that with increasing core counts and showing the performance scaling. Another annoyance is that you have to be extremely careful to test with enough memory to exceed the sum of all caching on the processors by a large amount, or your results will be quite inflated. I believe I have whipped both of these problems for Linux systems having gcc 4.2 or later, and the code to test is now available at: http://github.com/gregs1104/stream-scaling It adds all of the cache sizes, increases that by a whole order of magnitude to compute the test size to really minimize their impact, and chugs away more or less automatically trying all the core counts. The documentation includes an initial 6 systems I was able to get samples for, and they show a lot of the common things I've noticed before quite nicely. The upper limits of DDR2 systems even when you have lots of banks, how amazingly fast speeds to a single core are with recent Intel+DDR3/1600 systems, all stuff I've measured at a higher level are really higlighted with this low-level test. Given the changes to the test method and size computations since the earlier tests posted in the past thread here, I'm afraid I can't include any of those results in the table. Note that this includes the newer 48-core AMD server that Scott Marlowe posted results from earlier; the one you see in my README.rst sample results is not it, that's an older system with 8 sockets, less cores per processor, and slower RAM. There's still some concern in my mind about whether the test size was really big enough in the earlier sample Scott submitted to the list, and he actually has to do real work on that server for the moment before he can re-test. Will get that filled in eventually. If any of you into this sort of thing would like to contribute a result, I'd like to see the following (off-list please, I'll summarize on the page later, and let me know if you want to be credited or anonymous for the contribution): -Full output from the stream-scaling run -Output of "cat /proc/cpuinfo" on your server -Total amount of RAM in the server (including the output from "free" will suffice) -RAM topology and speed, if you know it. I can guess that in some cases if you don't know. -- Greg Smith, 2ndQuadrant US greg@2ndQuadrant.com Baltimore, MD PostgreSQL Training, Services and Support www.2ndQuadrant.us Author, "PostgreSQL 9.0 High Performance" Pre-ordering at: https://www.packtpub.com/postgresql-9-0-high-performance/book ^ permalink raw reply [nested|flat] 2+ messages in thread
* Re: Memory speed testing 2010-09-21 04:20 Memory speed testing Greg Smith <greg@2ndquadrant.com> @ 2010-09-27 16:53 ` Greg Smith <greg@2ndquadrant.com> 0 siblings, 0 replies; 2+ messages in thread From: Greg Smith @ 2010-09-27 16:53 UTC (permalink / raw) To: pgsql-performance Last bit of promotion here for this project: http://github.com/gregs1104/stream-scaling has been updated with a few more results anonymously submitted by list members here. The updated chart really fleshes out how the RAM scaling works on the older multi-socket AMD servers now. That's something that's been described on this list for years, but never really measured this clearly before to my knowledge. I have 4 and 8 socket examples in there now, showing DDR2/667 and DDR2/800. Also have some initial numbers on the DDR-3 based Phenom II processors too, which fit right in the middle of the Intel samples. They look like another round of good bang for the buck midrange desktop parts typical for AMD. -- Greg Smith, 2ndQuadrant US greg@2ndQuadrant.com Baltimore, MD PostgreSQL Training, Services and Support www.2ndQuadrant.us Author, "PostgreSQL 9.0 High Performance" Pre-ordering at: https://www.packtpub.com/postgresql-9-0-high-performance/book ^ permalink raw reply [nested|flat] 2+ messages in thread
end of thread, other threads:[~2010-09-27 16:53 UTC | newest] Thread overview: 2+ messages (download: mbox mbox.gz follow: Atom feed) -- links below jump to the message on this page -- 2010-09-21 04:20 Memory speed testing Greg Smith <greg@2ndquadrant.com> 2010-09-27 16:53 ` Greg Smith <greg@2ndquadrant.com>
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