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SubjectRe: [PATCH V5 RESEND 00/14] TopDown metrics support for Icelake
On Mon, Jan 06, 2020 at 12:29:05PM -0800, wrote:
> From: Kan Liang <>
> Icelake has support for measuring the level 1 TopDown metrics
> directly in hardware. This is implemented by an additional METRICS
> register, and a new Fixed Counter 3 that measures pipeline SLOTS.
> New in Icelake
> - Do not require generic counters. This allows to collect TopDown always
> in addition to other events.
> - Measuring TopDown per thread/process instead of only per core
> For the Ice Lake implementation of performance metrics, the values in
> PERF_METRICS MSR are derived from fixed counter 3. Software should start
> both registers, PERF_METRICS and fixed counter 3, from zero.
> Additionally, software is recommended to periodically clear both
> registers in order to maintain accurate measurements. The latter is
> required for certain scenarios that involve sampling metrics at high
> rates. Software should always write fixed counter 3 before write to

Do we really have to support this trainwreck? This is such ill designed
hardware, I'm loath to support it, it might encourage more such
'creative' things and we really don't need that.

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