linux-kernel - Re: [PATCH v3 00/12] perf/core: Generalise event exclusion checking

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Message-ID: <20181207172516.GB2044@edgewater-inn.cambridge.arm.com>
Date:   Fri, 7 Dec 2018 17:25:17 +0000
From:   Will Deacon <will.deacon@....com>
To:     Andrew Murray <andrew.murray@....com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        Mark Rutland <mark.rutland@....com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Russell King <linux@...linux.org.uk>, suzuki.poulose@....com,
        robin.murphy@....com, Michael Ellerman <mpe@...erman.id.au>,
        linux-kernel@...r.kernel.org, linux-alpha@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org
Subject: Re: [PATCH v3 00/12] perf/core: Generalise event exclusion checking

On Thu, Dec 06, 2018 at 04:47:17PM +0000, Andrew Murray wrote:
> Many PMU drivers do not have the capability to exclude counting events
> that occur in specific contexts such as idle, kernel, guest, etc. These
> drivers indicate this by returning an error in their event_init upon
> testing the events attribute flags.
> 
> However this approach requires that each time a new event modifier is
> added to perf, all the perf drivers need to be modified to indicate that
> they don't support the attribute. This results in additional boiler-plate
> code common to many drivers that needs to be maintained. Furthermore the
> drivers are not consistent with regards to the error value they return
> when reporting unsupported attributes.
> 
> This patchset allow PMU drivers to advertise their inability to exclude
> based on context via a new capability: PERF_PMU_CAP_NO_EXCLUDE. This
> allows the perf core to reject requests for exclusion events where there
> is no support in the PMU.
> 
> This is a functional change, in particular:
> 
>  - Some drivers will now additionally (but correctly) report unsupported
>    exclusion flags. It's typical for existing userspace tools such as
>    perf to handle such errors by retrying the system call without the
>    unsupported flags.
> 
>  - Drivers that do not support any exclusion that previously reported
>    -EPERM or -EOPNOTSUPP will now report -EINVAL - this is consistent
>    with the majority and results in userspace perf retrying without
>    exclusion.
> 
> All drivers touched by this patchset have been compile tested.

For the bits under arch/arm/ and drivers/perf:

Acked-by: Will Deacon <will.deacon@....com>

Note that I've queued the TX2 uncore PMU for 4.21 [1], which could also
benefit from your new flag.

Will

[1]
https://git.kernel.org/pub/scm/linux/kernel/git/will/linux.git/commit/?h=for-next/perf&id=69c32972d59388c041268e8206e8eb1acff29b9a