linux-kernel - Re: [RFC 00/11] perf: Enhancing perf to export processor hazard information

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Date:   Mon, 2 Mar 2020 17:33:29 -0800
From:   Andi Kleen <ak@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ravi Bangoria <ravi.bangoria@...ux.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        eranian@...gle.com, mpe@...erman.id.au, paulus@...ba.org,
        mingo@...hat.com, acme@...nel.org, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
        namhyung@...nel.org, adrian.hunter@...el.com,
        kan.liang@...ux.intel.com, alexey.budankov@...ux.intel.com,
        yao.jin@...ux.intel.com, robert.richter@....com,
        kim.phillips@....com, maddy@...ux.ibm.com
Subject: Re: [RFC 00/11] perf: Enhancing perf to export processor hazard
 information

On Mon, Mar 02, 2020 at 11:13:32AM +0100, Peter Zijlstra wrote:
> On Mon, Mar 02, 2020 at 10:53:44AM +0530, Ravi Bangoria wrote:
> > Modern processors export such hazard data in Performance
> > Monitoring Unit (PMU) registers. Ex, 'Sampled Instruction Event
> > Register' on IBM PowerPC[1][2] and 'Instruction-Based Sampling' on
> > AMD[3] provides similar information.
> > 
> > Implementation detail:
> > 
> > A new sample_type called PERF_SAMPLE_PIPELINE_HAZ is introduced.
> > If it's set, kernel converts arch specific hazard information
> > into generic format:
> > 
> >   struct perf_pipeline_haz_data {
> >          /* Instruction/Opcode type: Load, Store, Branch .... */
> >          __u8    itype;
> >          /* Instruction Cache source */
> >          __u8    icache;
> >          /* Instruction suffered hazard in pipeline stage */
> >          __u8    hazard_stage;
> >          /* Hazard reason */
> >          __u8    hazard_reason;
> >          /* Instruction suffered stall in pipeline stage */
> >          __u8    stall_stage;
> >          /* Stall reason */
> >          __u8    stall_reason;
> >          __u16   pad;
> >   };
> 
> Kim, does this format indeed work for AMD IBS?

Intel PEBS has a similar concept for annotation of memory accesses,
which is already exported through perf_mem_data_src. This is essentially
an extension. It would be better to have something unified here. 
Right now it seems to duplicate at least part of the PEBS facility.

-Andi