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Date: Fri, 14 Oct 2011 03:08:23 -0700 (PDT) From: David Rientjes <rientjes@...gle.com> To: "Oberman, Laurence (HAS GSE)" <Laurence.Oberman@...com> cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "Seger, Mark" <mark.seger@...com>, "Cabaniols, Sebastien" <Sebastien.Cabaniols@...com> Subject: Re: Regression in reading /proc/stat in the newer kernels with large SMP and NUMA configurations On Fri, 14 Oct 2011, Oberman, Laurence (HAS GSE) wrote: > On the 2.6.16.x series sles or 2.6.18.x RHEL kernels each read takes 84 > us. > > dl785sles:~/wrk # cat 2.6.16.60-0.87.1-smp.log Opened, read and closed 8640 times and read total of 13996800 bytes > % time seconds usecs/call calls errors syscall > ------ ----------- ----------- --------- --------- ---------------- > 99.41 0.725717 84 8641 read > 0.38 0.002768 0 8642 open > 0.21 0.001539 0 8642 close > 0.00 0.000000 0 1 write > 0.00 0.000000 0 3 fstat > 0.00 0.000000 0 8 mmap > 0.00 0.000000 0 2 mprotect > 0.00 0.000000 0 1 munmap > 0.00 0.000000 0 1 brk > 0.00 0.000000 0 1 1 access > 0.00 0.000000 0 1 madvise > 0.00 0.000000 0 1 execve > 0.00 0.000000 0 1 arch_prctl > ------ ----------- ----------- --------- --------- ---------------- > 100.00 0.730024 25945 1 total > > On the 2.6.38.4 kernel each read takes > 6ms > > dl785sles:~/wrk # cat 2.6.38.4-smp.log > Opened, read and closed 8640 times and read total of 86235840 bytes > % time seconds usecs/call calls errors syscall > ------ ----------- ----------- --------- --------- ---------------- > 100.00 59.021650 6830 8641 read > 0.00 0.000520 0 8642 open > 0.00 0.000425 0 8642 close > 0.00 0.000000 0 1 write > 0.00 0.000000 0 3 fstat > 0.00 0.000000 0 9 mmap > 0.00 0.000000 0 2 mprotect > 0.00 0.000000 0 1 munmap > 0.00 0.000000 0 1 brk > 0.00 0.000000 0 1 1 access > 0.00 0.000000 0 1 madvise > 0.00 0.000000 0 1 execve > 0.00 0.000000 0 1 arch_prctl > ------ ----------- ----------- --------- --------- ---------------- > 100.00 59.022595 25946 1 total > The overhead is probably in kstat_irqs_cpu() which is called for each possible irq for each of the 32 possible cpus, and /proc/stat actually does the sum twice. You would see the same type of overhead with /proc/interrupts if it wasn't masked by the locking that it requires to safely read irq_desc. "dmesg | grep nr_irqs" will show how many percpu variables are being read for every cpu twice. -- 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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