From mboxrd@z Thu Jan 1 00:00:00 1970 From: mwilck@suse.com (Martin Wilck) Date: Tue, 11 Sep 2018 08:55:27 +0200 Subject: CPU frequency variations In-Reply-To: References: Message-ID: <830fa5e6db6e7ba24a81eea4a18be8a1379b7be6.camel@suse.com> On Tue, 2018-09-11@00:02 +0530, Joshi wrote: > While doing some I/O polling related experiments/optimization, I felt > the need to eliminate fluctuations (in I/O performance) caused by CPU > frequency variations. > > During benchmarks (and I mean storage ones), in order to keep running > CPU at nearly constant high frequency, I tried > things such as - performance governor, bios-based performance > settings, explicit setting of sysfs cpu scaling max counters, kernel > parameters to disable cpufreq etc. > Some of above helped; On machines with less number of CPUs. While > nothing seems to help on relatively heavyweight machines. > Such as on this- Intel Xeon E5-2690 v3 @2.6 GHz, 2 NUMA nodes, 24 > cpus each. > > Often storage-benchmark seem to suffer because there are more number > of CPUs available; Binding it to single/few CPUs help in seeing > better > numbers. > > May I know how you deal with CPU frequency variations during > benchmarks. Are you certain that it's frequency variations that hurt you? Maybe your CPUs go to deep sleep states? Have you tried e.g. "intel_idle.max_cstate=0"? Martin -- Dr. Martin Wilck , Tel. +49 (0)911 74053 2107 SUSE Linux GmbH, GF: Felix Imend?rffer, Jane Smithard, Graham Norton HRB 21284 (AG N?rnberg)