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Re: [PATCH 0/3]measure SMI cost

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  Re: [PATCH 0/3]measure SMI cost Stephane Eranian <eranian@google.com> - 2017-04-01 00:00 +0200
    RE: [PATCH 0/3]measure SMI cost "Liang, Kan" <kan.liang@intel.com> - 2017-04-01 03:50 +0200

#1614306 — Re: [PATCH 0/3]measure SMI cost

On Thu, Mar 23, 2017 at 11:25 AM,  <kan.liang@intel.com> wrote:
> From: Kan Liang <Kan.liang@intel.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?
I
> Here is an example output.
>
>  Performance counter stats for 'sudo echo ':
>
> SMI cycles%          SMI#
>     0.1%              1
>
>        0.010858678 seconds time elapsed
>
>
> Kan Liang (3):
>   perf/x86: add sysfs entry to freeze counter on SMI
>   tools lib api fs: Add sysfs__write_int function
>   perf stat: Add support to measure SMI cost
>
>  arch/x86/events/core.c                 | 10 +++++++
>  arch/x86/events/intel/core.c           | 48 ++++++++++++++++++++++++++++++++++
>  arch/x86/events/perf_event.h           |  3 +++
>  arch/x86/include/asm/msr-index.h       |  1 +
>  tools/lib/api/fs/fs.c                  | 29 ++++++++++++++++++++
>  tools/lib/api/fs/fs.h                  |  4 +++
>  tools/perf/Documentation/perf-stat.txt |  9 +++++++
>  tools/perf/builtin-stat.c              | 48 ++++++++++++++++++++++++++++++++++
>  tools/perf/util/stat-shadow.c          | 33 +++++++++++++++++++++++
>  tools/perf/util/stat.c                 |  2 ++
>  tools/perf/util/stat.h                 |  2 ++
>  11 files changed, 189 insertions(+)
>
> --
> 2.7.4
>

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#1614351

> On Thu, Mar 23, 2017 at 11:25 AM,  <kan.liang@intel.com> wrote:
> > From: Kan Liang <Kan.liang@intel.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

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