linux-kernel - Re: [RFC] bpf: lbr: enable reading LBR from tracing bpf programs

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Message-ID: <2DB56175-ECFD-492B-A577-866D39A445E5@fb.com>
Date:   Thu, 19 Aug 2021 18:45:11 +0000
From:   Song Liu <songliubraving@...com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     "open list:BPF (Safe dynamic programs and tools)" 
        <bpf@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "acme@...nel.org" <acme@...nel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        Kernel Team <Kernel-team@...com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        "Like Xu" <like.xu@...ux.intel.com>,
        Alexey Budankov <alexey.budankov@...ux.intel.com>
Subject: Re: [RFC] bpf: lbr: enable reading LBR from tracing bpf programs

Hi Peter,

> On Aug 19, 2021, at 11:27 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> 
> On Thu, Aug 19, 2021 at 06:22:07PM +0000, Song Liu wrote:
> 
>>> And if we're going to be adding new pmu::methods then I figure one that
>>> does the whole sample state might be more useful.
>> 
>> What do you mean by "whole sample state"? To integrate with exiting
>> perf_sample_data, like perf_output_sample()?
> 
> Yeah, the PMI can/does set more than data->br_stack, but I'm now
> thinking that without an actual PMI, much of that will not be possible.
> br_stack is special here.
> 
> Oh well, carry on I suppose.

Thanks again for these information and suggestions. I will try to put them
together in the code and send the patches. 

Song