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Date: Mon, 25 Aug 2008 11:23:10 +0200 From: Peter Zijlstra <peterz@...radead.org> To: edwin <edwintorok@...il.com> Cc: Ingo Molnar <mingo@...e.hu>, rml@...h9.net, Linux Kernel <linux-kernel@...r.kernel.org>, "Thomas Gleixner mingo@...hat.com" <tglx@...utronix.de>, "H. Peter Anvin" <hpa@...or.com> Subject: Re: Quad core CPUs loaded at only 50% when running a CPU and mmap intensive multi-threaded task On Mon, 2008-08-25 at 10:04 +0300, edwin wrote: > Peter Zijlstra wrote: > > On Mon, 2008-08-25 at 00:01 +0300, Török Edwin wrote: > > > >> Hi Ingo, > >> > >> When I run clamd (www.clamav.net), I can only get to load my CPU 50% > >> (according to top), and disks at 30% (according to iostat -x 3), > >> regardless how many threads I set (I tried 4, 8, 16, 32). > >> > > > > > > Can you share your .config, and prehaps tell what kernel version did > > work for you? > > Sorry, I forgot to include the .config, its at the end of this mail (the > cfs debug info output included the .config though) > > Well, I just bought this new box, so there isn't a kernel version that I > know that worked on this hardware (but I am trying to boot some older > versions now). > However on my previous box (Athlon64, non-SMP) I have never seen such a > problem (that the CPU is loaded only 50% with clamd) and I've been > running 2.6.26 and 2.6.27-rc4 there too. > > Details below, short summary here: > 2.6.24: WORKS, clamd 400% CPU, testprogram runs in 27.4 seconds, 67% CPU > load; and 28.5 seconds w/o setting affinity > 2.6.25+: DOES NOT WORK, clamd 200%-300% CPU, testprogram runs in 38-40 > seconds, 48-48% CPU load, and 47-56 seconds w/o setting affinity > > Debian has 2.6.18, 2.6.22, 2.6.24, 2.6.25, 2.6.26. > 2.6.22 won't work with my lvm, so I can't boot that, so I tried 2.6.24: > > 2.6.24 doesn't have sched_debug enabled in the stock kernel > unfortunately, but the output of cfs-debug-info.sh is available here, > maybe it contains some useful info: > http://edwintorok.googlepages.com/testrun-1219645937.tar.gz > > Is this enough info for you to reproduce the problem, or do you want me > to try and bisect? No, I think I know what's going on.. mmap() and munmap() need to take the mmap_sem for writing (since they modify the memory map) and you let each thread (one for each cpu) take that process wide lock, twice, for a million times. Guess what happens ;-) -- 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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