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Message-Id: <E363A887-933C-41FE-A55A-13740B273904@gmail.com> Date: Tue, 23 Mar 2010 17:37:44 +0100 From: Anton Starikov <ant.starikov@...il.com> To: Anton Starikov <ant.starikov@...il.com> Cc: linux-kernel@...r.kernel.org Subject: Re: possible huge regress Created bug report with binary test-case. https://bugzilla.kernel.org/show_bug.cgi?id=15618 On Mar 23, 2010, at 4:43 PM, Anton Starikov wrote: > Hi, > > We have benchmarked some multithreaded code here on 16-core/4-way opteron 8356 host on number of kernels (see below) and found strange results. > Up to 8 threads we didn't see any noticeable differences in performance, but starting from 9 threads performance diverges substantially. I provide here results for 14 threads > > 2.6.18-164.11.1.el5 (centos) > > user time: ~60 sec > sys time: ~12 sec > > 2.6.32.9-70.fc12.x86_64 (fedora-12) > > user time: ~60 sec > sys time: ~75 sec > > 2.6.33-0.46.rc8.git1.fc13.x86_64 (fedora-12 + rawhide kernel) > > user time: ~60 sec > sys time: ~300 sec > > In all three cases real time corresponds to given numbers. > > Binary used for all three cases is exactly the same (compiled on centos). > Setups for all three cases so identical as possible (last two - the sanme fedore-12 booted with different kernels). > I submit to LKLM because I feel that this is some general kernel issue rather than RH-flavored kernel issue. > > What can be reason of this regress in performance? Is it possible to tune something to recover performance on 2.6.18 kernel? > > I perf'ed on 2.6.32.9-70.fc12.x86_64 kernel > > report (top part only): > > 43.64% dve22lts-mc [kernel] [k] _spin_lock_irqsave > 32.93% dve22lts-mc ./dve22lts-mc [.] DBSLLlookup_ret > 5.37% dve22lts-mc ./dve22lts-mc [.] SuperFastHash > 3.76% dve22lts-mc /lib64/libc-2.11.1.so [.] __GI_memcpy > 2.60% dve22lts-mc [kernel] [k] clear_page_c > 1.60% dve22lts-mc ./dve22lts-mc [.] index_next_dfs > > stat: > 129875.554435 task-clock-msecs # 10.210 CPUs > 1883 context-switches # 0.000 M/sec > 17 CPU-migrations # 0.000 M/sec > 2695310 page-faults # 0.021 M/sec > 298370338040 cycles # 2297.356 M/sec > 130581778178 instructions # 0.438 IPC > 42517143751 cache-references # 327.368 M/sec > 101906904 cache-misses # 0.785 M/sec > > callgraph: > > 53.09% dve22lts-mc [kernel] [k] > _spin_lock_irqsave > | > |--49.90%-- __down_read_trylock > | down_read_trylock > | do_page_fault > | page_fault > | | > | |--99.99%-- __GI_memcpy > | | | > | | |--84.28%-- (nil) > | | | > | | |--9.78%-- 0x100000000 > | | | > | | --5.94%-- 0x1 > | --0.01%-- > [...] > > | > |--49.39%-- __up_read > | up_read > | | > | |--100.00%-- do_page_fault > | | page_fault > | | | > | | |--99.99%-- __GI_memcpy > | | | | > | | | |--84.18%-- (nil) > | | | | > | | | |--10.13%-- 0x100000000 > | | | | > | | | --5.69%-- 0x1 > | | --0.01%-- > [...] > > | --0.00%-- > [...] > > --0.72%-- > [...] > > > Anton. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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