From mboxrd@z Thu Jan 1 00:00:00 1970 From: keith.busch@linux.intel.com (Keith Busch) Date: Mon, 10 Sep 2018 13:00:40 -0600 Subject: CPU frequency variations In-Reply-To: References: Message-ID: <20180910190040.GA7867@localhost.localdomain> On Tue, Sep 11, 2018@12:02:25AM +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. Just to get all the CPU's to use the highest performing scaling governor: echo performance | tee /sys/devices/system/cpu/cpufreq/policy*/scaling_governor But it sounds like you've alraedy done that.