Messages in this thread | | | Date | Fri, 10 Jan 2020 14:17:49 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH V5 RESEND 00/14] TopDown metrics support for Icelake |
| |
On Mon, Jan 06, 2020 at 12:29:05PM -0800, kan.liang@linux.intel.com wrote: > From: Kan Liang <kan.liang@linux.intel.com> > > 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 > PERF_METRICS.
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.
| |