Messages in this thread |  | | | Subject | Re: Hyperthreading on Core i7s: To use or not to use? | | From | peng huang <> | | Date | Tue, 26 Jan 2010 22:11:52 +0900 |
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Hello,
I have been done some benchmark things on the processors with HT, if you run lots of processes/threads that more than the physical cores,may be you should enable the HT to get more benefits. #unless your processes cause some cache competitions.
I will send you some test data later.
-huang
2010-01-26 (火) の 10:56 +0000 に Daniel J Blueman さんは書きました: > On Jan 26, 10:10 am, Justin Piszcz <jpiszcz@lucidpixels.com> wrote: > > Hello, > > Should the 'correct' kernel [CPU] configuration for a core i7 860/870..? > > > > - Multi-core support > > - Cores: 8 > > - SMT: Enabled/ON > > > > From CONFIG_SCHED_SMT: > > > > . SMT scheduler support improves the CPU scheduler's decision making . > > . when dealing with Intel Pentium 4 chips with HyperThreading at a . > > . cost of slightly increased overhead in some places. If unsure say . > > . N here. . > > > > Does this also 'help' and/or 'apply' as much when dealing with Core i7s? > > > > -- > > > > Quick little benchmark (pbzip2 -9 linux kernel source), the benchmark is > > really within the noise (8 on/off) > > - Multicore(8)/HT(Off) = 73.72user 0.33system 0:09.50elapsed 779%CPU (0avgtext+0avgdata 458528maxresident > > - Multicore(8)/HT(On) = 74.28user 0.40system 0:09.67elapsed 772%CPU (0avgtext+0avgdata 428304maxresident > > - Multicore(4)/HT(On) = 68.76user 0.30system 0:17.44elapsed 396%CPU (0avgtext+0avgdata 213616maxresident)k > > > > -- > > > > Has anyone done any in-depth benchmarking for the core i7s that have multiple > > cores and HT disabled/enabled? > > With my Dell Studio 15 (model 1557) laptop, there is no option to > disable HT in the current BIOS, so booting with maxcpus=4 (since the > kernel enumerates non-sibling cores first) gave me a 5-15% speedup on > some large image processing (convolution, FFTs, conversion) on all > available cores, presumably due to better cache efficiency. > > Booting with maxcpus=4 prevents any of the cores sitting in C6, needed > for turbo-boost and a lower thermal profile, though I did find > scheduling latency and responsiveness better under load booting with > maxcpus=4, so favour this when plugged in. > > Clearly, having the BIOS option allows benefit to certain applications > - Dell should give their users the choice! > > Perhaps the 'noht' boot option should be reintroduced to initialise > all cores, but only expose non-sibling cores to the OS (thus allowing > C6)? > > Daniel > > tip: modprobe msr and use turbostat to monitor turbo-boost and C-state > residency: http://bugzilla.kernel.org/attachment.cgi?id=24673
-- peng huang <huangpeng.linux@gmail.com>
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