linux-kernel - Re: [linus:master] [xfs] 2edf06a50f: fsmark.files_per

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Message-ID: <b14bc8d1c2652ffc5e35b68279ee36ecadbfa83b.camel@intel.com>
Date:   Tue, 16 May 2023 03:07:56 +0000
From:   "Zhang, Rui" <rui.zhang@...el.com>
To:     "david@...morbit.com" <david@...morbit.com>,
        "djwong@...nel.org" <djwong@...nel.org>,
        "Tang, Feng" <feng.tang@...el.com>
CC:     lkp <lkp@...el.com>, "Huang, Ying" <ying.huang@...el.com>,
        "Yin, Fengwei" <fengwei.yin@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>,
        "Sang, Oliver" <oliver.sang@...el.com>,
        "dchinner@...hat.com" <dchinner@...hat.com>,
        "oe-lkp@...ts.linux.dev" <oe-lkp@...ts.linux.dev>
Subject: Re: [linus:master] [xfs]  2edf06a50f:  fsmark.files_per_sec -5.7%
 regression


> > > Also for the turbostat.Bzy_MHz diff, IIUC, 0Day always uses
> > > 'performance' cpufreq governor. And as the test case is running
> > > 32 thread in a platform with 96 CPUs, there are many CPUs in idle
> > > state in average, and I suspect the Bzy_MHz may be calculated 
> > > considering those cpufreq and cpuidle factors.
> > 
> > If "busy MHz" includes the speed of idle CPUs, then it's not really
> > a measure of the speed of "busy" CPUs. If what you say is true,
> > then
> > it is, at best, badly names - it would just be the "average Mhz",
> > right?
> 
> I found the turbostat.c in kernel tree tools/power/x86/turbostat/
> 
> if (DO_BIC(BIC_Bzy_MHz)) {
> 	if (has_base_hz)
> 		outp +=
> 		    sprintf(outp, "%s%.0f", (printed++ ? delim : ""),
> base_hz / units * t->aperf / t->mperf);
> 	else
> 		outp += sprintf(outp, "%s%.0f", (printed++ ? delim :
> ""),
> 				tsc / units * t->aperf / t->mperf /
> interval_float);
> }
> 
> Rui Zhang told me the 'aperf' is the actual cpu cycles of a CPU in a
> period of time, and it only count when CPU is in C0 state, and will
> stop counting when cpu is in idle power state. Like in one second
> interval, if the CPU spends 500 ms running at 1000 MHz, and the other
> 500 ms in idle, then the Bzy_MHz will be shown 500 MHz.

Bzy_MHz will show 1000 MHz because it is the actual frequency when CPU
is in C0.
Avg_MHz will show 500 MHz because it is the average frequency including
the CPU idle time.

thanks,
rui