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SubjectRe: [PATCH 0/3]measure SMI cost
On Thu, 23 Mar 2017, wrote:

> From: Kan Liang <>
> 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
> 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.

That's only true for performance oriented analysis, but for analyzing the
root cause of latencies the actual cycles are definitely interesting.



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