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Date: Fri, 17 Apr 2009 13:45:05 -0400 (EDT) From: Christoph Lameter <cl@...ux.com> To: Ingo Molnar <mingo@...e.hu> cc: Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org Subject: Re: Scheduler regression: Too frequent timer interrupts(?) Ok I made some changes to the latencytest program (gentwo.org/ll). I hope you can tell me what exactly you would consider meaningful numbers. Here is a sample execution with a granularity of 1usec and a bucket size of 1usec and the mininum set to zero (2.6.29 HZ=1000): latencytest -d -m0 -b1000 CPUs: Freq=3.16Ghz Processors=8 Cores=4 cacheline_size=64 Intel(R) Xeon(R) CPU X5460 @ 3.16GHz 522 involuntary context switches 207231729 (100.00000000%) variances in 10.00 seconds: minimum 0.04us maximum 109.58us average 0.05us usecs percent samples ------------------------- 0.0 100.0 207221180 2.0 0.0 35 3.0 0.0 3691 4.0 0.0 4637 5.0 0.0 891 6.0 0.0 464 7.0 0.0 90 8.0 0.0 83 9.0 0.0 44 10.0 0.0 42 11.0 0.0 42 12.0 0.0 171 13.0 0.0 150 14.0 0.0 44 15.0 0.0 19 16.0 0.0 23 17.0 0.0 16 18.0 0.0 9 19.0 0.0 15 20.0 0.0 2 21.0 0.0 6 22.0 0.0 4 23.0 0.0 4 24.0 0.0 13 25.0 0.0 2 27.0 0.0 2 29.0 0.0 2 30.0 0.0 3 31.0 0.0 1 32.0 0.0 3 33.0 0.0 2 34.0 0.0 1 36.0 0.0 2 37.0 0.0 1 38.0 0.0 1 39.0 0.0 7 40.0 0.0 7 41.0 0.0 9 42.0 0.0 3 43.0 0.0 1 44.0 0.0 1 46.0 0.0 1 49.0 0.0 1 50.0 0.0 1 57.0 0.0 1 61.0 0.0 1 109.0 0.0 1 Setting the mininum to 1usec yields: christoph@...HITW00139:~/lldiag-0.2$ ./latencytest -d -m1000 -b1000 CPUs: Freq=3.16Ghz Processors=8 Cores=4 cacheline_size=64 Intel(R) Xeon(R) CPU X5460 @ 3.16GHz 247597652 samples below 1000 nsec 28 involuntary context switches 10011 (0.00404309%) variances in 10.00 seconds: minimum 3.20us maximum 336.82us average 5.35us usecs percent samples ------------------------- 3.0 6.4 645 4.0 28.6 2866 5.0 57.7 5781 6.0 4.5 448 7.0 1.1 113 8.0 0.4 39 9.0 0.6 59 10.0 0.2 19 11.0 0.0 1 12.0 0.0 2 13.0 0.0 4 14.0 0.0 1 15.0 0.0 1 16.0 0.0 2 20.0 0.0 3 26.0 0.0 1 28.0 0.0 1 30.0 0.0 1 37.0 0.0 1 38.0 0.0 1 43.0 0.0 1 45.0 0.0 3 46.0 0.0 1 47.0 0.0 2 48.0 0.0 1 53.0 0.0 1 55.0 0.0 1 56.0 0.0 4 57.0 0.0 4 61.0 0.0 1 76.0 0.0 1 93.0 0.0 1 336.0 0.0 1 More fine grained resolution (100ns do not count measurements below 100ns): latencytest -d -m100 -b100 CPUs: Freq=3.16Ghz Processors=8 Cores=4 cacheline_size=64 Intel(R) Xeon(R) CPU X5460 @ 3.16GHz 266619352 samples below 100 nsec 19 involuntary context switches 13254 (0.00497088%) variances in 10.00 seconds: minimum 0.10us maximum 143.63us average 3.63us usecs percent samples ------------------------- 0.1 23.7 3141 0.2 0.7 87 0.3 0.1 12 0.5 0.0 1 0.6 0.0 1 1.9 0.1 17 2.0 0.4 47 2.1 1.0 127 2.2 2.3 309 2.3 0.3 35 2.4 0.2 25 2.5 0.2 22 2.6 0.2 23 2.7 2.0 267 2.8 4.2 559 2.9 0.4 52 3.0 1.1 143 3.1 1.5 198 3.2 1.1 149 3.3 0.7 97 3.4 0.6 78 3.5 0.6 83 3.6 0.9 121 3.7 0.8 112 3.8 4.1 547 3.9 1.5 194 4.0 0.3 42 4.1 0.1 15 4.2 0.2 23 4.3 0.8 108 4.4 0.5 63 4.5 0.2 20 4.6 0.2 25 4.7 0.2 28 4.8 0.3 44 4.9 0.2 24 5.0 1.0 126 5.1 3.1 414 5.2 18.0 2385 5.3 6.5 857 5.4 4.9 656 5.5 2.5 335 5.6 3.4 448 5.7 3.4 445 5.8 2.0 268 5.9 0.9 116 6.0 0.4 54 6.1 0.2 22 6.2 0.3 36 6.3 0.1 17 6.4 0.1 10 6.5 0.1 11 6.6 0.1 9 6.7 0.1 9 6.8 0.1 8 6.9 0.0 4 7.0 0.1 8 7.1 0.0 6 7.2 0.1 7 7.3 0.1 14 7.4 0.1 7 7.5 0.0 4 7.6 0.0 3 7.7 0.0 6 7.8 0.1 7 7.9 0.0 6 8.0 0.0 5 8.1 0.0 4 8.2 0.0 3 8.3 0.0 2 8.4 0.0 2 The group around 5usec is likely the timer interrupt. -- 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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