linux-kernel - RE: [PATCH 0/3]measure SMI cost

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Date:   Sat, 1 Apr 2017 01:41:07 +0000
From:   "Liang, Kan" <kan.liang@...el.com>
To:     Stephane Eranian <eranian@...gle.com>
CC:     Peter Zijlstra <peterz@...radead.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Jiri Olsa" <jolsa@...nel.org>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>
Subject: RE: [PATCH 0/3]measure SMI cost



> On Thu, Mar 23, 2017 at 11:25 AM,  <kan.liang@...el.com> wrote:
> > From: Kan Liang <Kan.liang@...el.com>
> >
> > Currently, there is no way to measure the time cost in System
> > management mode (SMM) by perf.
> >
> > Intel perfmon supports FREEZE_WHILE_SMM bit in IA32_DEBUGCTL. Once
> it
> > sets, the PMU core counters will freeze on SMI handler. But it will
> > not have an effect on free running counters. E.g. APERF counter.
> > The cost of SMI can be measured by (aperf - cycles).
> >
> > A new sysfs entry /sys/device/cpu/freeze_on_smi is introduced to set
> > FREEZE_WHILE_SMM bit in IA32_DEBUGCTL.
> >
> > A new --smi-cost mode in perf stat is implemented to measure the SMI
> > cost by calculating cycles and aperf results. In practice, the
> > percentages of SMI cycles should be more useful than absolute value.
> > So the output will be the percentage of SMI cycles and SMI#.
> >
> You are talking about the percentage of what cycles?
> Wallclock, unhalted_ref_cycles, unhalted_core_cycles?

Unhalted core cycles.

Thanks,
Kan