linux-kernel - Re: [PATCH v4 05/13] arm: perf: conditionally use PERF_PMU_CAP_NO

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Date:   Tue, 8 Jan 2019 11:28:02 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andrew Murray <andrew.murray@....com>
Cc:     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>,
        Will Deacon <will.deacon@....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>,
        x86@...nel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-alpha@...r.kernel.org
Subject: Re: [PATCH v4 05/13] arm: perf: conditionally use
 PERF_PMU_CAP_NO_EXCLUDE

On Mon, Jan 07, 2019 at 04:27:22PM +0000, Andrew Murray wrote:
> @@ -393,9 +386,8 @@ __hw_perf_event_init(struct perf_event *event)
>  	/*
>  	 * Check whether we need to exclude the counter from certain modes.
>  	 */
> +	if (armpmu->set_event_filter &&
> +	    armpmu->set_event_filter(hwc, &event->attr)) {
>  		pr_debug("ARM performance counters do not support "
>  			 "mode exclusion\n");
>  		return -EOPNOTSUPP;

This then requires all set_event_filter() implementations to check all
the various exclude options; also, set_event_filter() failing then
returns with -EOPNOTSUPP instead of the -EINVAL the CAP_NO_EXCLUDE
generates, which is again inconsitent.

If I look at (the very first git-grep found me)
armv7pmu_set_event_filter(), then I find it returning -EPERM (again
inconsistent but irrelevant because the actual value is not preserved)
for exclude_idle.

But it doesn't seem to check exclude_host at all for example.

> @@ -867,6 +859,9 @@ int armpmu_register(struct arm_pmu *pmu)
>  	if (ret)
>  		return ret;
>  
> +	if (!pmu->set_event_filter)
> +		pmu->pmu.capabilities |= PERF_PMU_CAP_NO_EXCLUDE;
> +
>  	ret = perf_pmu_register(&pmu->pmu, pmu->name, -1);
>  	if (ret)
>  		goto out_destroy;
> -- 
> 2.7.4
>