linux-kernel - Re: [PATCH V2 1/5] powerpc/perf: Expose processor pipeline stage cycles using PERF_SAMPLE_WEIGHT

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Date:   Thu, 25 Mar 2021 15:38:01 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Madhavan Srinivasan <maddy@...ux.ibm.com>,
        Athira Rajeev <atrajeev@...ux.vnet.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org, mpe@...erman.id.au,
        jolsa@...nel.org, ravi.bangoria@...ux.ibm.com, kjain@...ux.ibm.com,
        kan.liang@...ux.intel.com
Subject: Re: [PATCH V2 1/5] powerpc/perf: Expose processor pipeline stage
 cycles using PERF_SAMPLE_WEIGHT_STRUCT

On Thu, Mar 25, 2021 at 10:01:35AM -0300, Arnaldo Carvalho de Melo wrote:
> Em Wed, Mar 24, 2021 at 10:05:23AM +0530, Madhavan Srinivasan escreveu:
> > 
> > On 3/22/21 8:27 PM, Athira Rajeev wrote:
> > > Performance Monitoring Unit (PMU) registers in powerpc provides
> > > information on cycles elapsed between different stages in the
> > > pipeline. This can be used for application tuning. On ISA v3.1
> > > platform, this information is exposed by sampling registers.
> > > Patch adds kernel support to capture two of the cycle counters
> > > as part of perf sample using the sample type:
> > > PERF_SAMPLE_WEIGHT_STRUCT.
> > > 
> > > The power PMU function 'get_mem_weight' currently uses 64 bit weight
> > > field of perf_sample_data to capture memory latency. But following the
> > > introduction of PERF_SAMPLE_WEIGHT_TYPE, weight field could contain
> > > 64-bit or 32-bit value depending on the architexture support for
> > > PERF_SAMPLE_WEIGHT_STRUCT. Patches uses WEIGHT_STRUCT to expose the
> > > pipeline stage cycles info. Hence update the ppmu functions to work for
> > > 64-bit and 32-bit weight values.
> > > 
> > > If the sample type is PERF_SAMPLE_WEIGHT, use the 64-bit weight field.
> > > if the sample type is PERF_SAMPLE_WEIGHT_STRUCT, memory subsystem
> > > latency is stored in the low 32bits of perf_sample_weight structure.
> > > Also for CPU_FTR_ARCH_31, capture the two cycle counter information in
> > > two 16 bit fields of perf_sample_weight structure.
> > 
> > Changes looks fine to me.
> > 
> > Reviewed-by: Madhavan Srinivasan <maddy@...ux.ibm.com>
> 
> So who will process the kernel bits? I'm merging the tooling parts,

I was sorta expecting these to go through the powerpc tree. Let me know
if you want them in tip/perf/core instead.