linux-kernel - Re: [PATCH 0/8] arm64/perf: Enable branch stack sampling

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Date:   Tue, 5 Jul 2022 13:09:07 +0100
From:   Will Deacon <will@...nel.org>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        peterz@...radead.org, acme@...nel.org, mark.rutland@....com,
        Catalin Marinas <catalin.marinas@....com>,
        James Clark <james.clark@....com>,
        Rob Herring <robh@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        linux-perf-users@...r.kernel.org
Subject: Re: [PATCH 0/8] arm64/perf: Enable branch stack sampling

On Tue, Jun 28, 2022 at 01:10:05PM +0530, Anshuman Khandual wrote:
> 
> 
> On 6/27/22 16:31, Will Deacon wrote:
> > On Mon, Jun 13, 2022 at 03:31:11PM +0530, Anshuman Khandual wrote:
> >> This series enables perf branch stack sampling support on arm64 platform
> >> via a new arch feature called Branch Record Buffer Extension (BRBE). All
> >> relevant register definitions could be accessed here.
> >>
> >> https://developer.arm.com/documentation/ddi0601/2021-12/AArch64-Registers
> >>
> >> This series applies on v5.19-rc2 after the BRBE related perf ABI changes series
> >> (V6) that was posted earlier.
> >>
> >> https://lore.kernel.org/linux-arm-kernel/20220610035101.424112-1-anshuman.khandual@arm.com/
> >>
> >> Following issues remain inconclusive
> >>
> >> - Jame's concerns regarding permission inadequacy related to perfmon_capable()
> >> - Jame's concerns regarding using perf_event_paranoid along with perfmon_capable()
> > 
> > afaict, the capability stuff remains unresolved with the SPE driver, so I'd
> > really like to see it fixed there first before we add more broken drivers.
> > 
> > https://lore.kernel.org/r/20220118100702.GB16547@willie-the-truck
> 
> Hello Will,
> 
> I did go through the above mentioned thread, but could not understand (clear
> enough) - what needs to be done. Could you please help summerize the problem
> and possible solutions which I can start looking into. Thank you.

I don't recall any details beyond what was discussed in the thread. Your
best bet is probably to talk to James (Clark) and German, as they reported
the issue initially and you all work for the same company...

Will