linux-kernel - Re: [RFC v2] perf: Rewrite core context handling

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Message-ID: <YqdP4NExuwOHdC0G@hirez.programming.kicks-ass.net>
Date:   Mon, 13 Jun 2022 16:55:28 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ravi Bangoria <ravi.bangoria@....com>
Cc:     acme@...nel.org, alexander.shishkin@...ux.intel.com,
        jolsa@...hat.com, namhyung@...nel.org, songliubraving@...com,
        eranian@...gle.com, alexey.budankov@...ux.intel.com,
        ak@...ux.intel.com, mark.rutland@....com, megha.dey@...el.com,
        frederic@...nel.org, maddy@...ux.ibm.com, irogers@...gle.com,
        kim.phillips@....com, linux-kernel@...r.kernel.org,
        santosh.shukla@....com
Subject: Re: [RFC v2] perf: Rewrite core context handling

On Mon, Jun 13, 2022 at 04:35:11PM +0200, Peter Zijlstra wrote:
> @@ -12125,6 +12232,8 @@ SYSCALL_DEFINE5(perf_event_open,
>  		goto err_task;
>  	}
>  
> +	// XXX premature; what if this is allowed, but we get moved to a PMU
> +	// that doesn't have this.
>  	if (is_sampling_event(event)) {
>  		if (event->pmu->capabilities & PERF_PMU_CAP_NO_INTERRUPT) {
>  			err = -EOPNOTSUPP;

No; this really should be against the event's native PMU. If the event
can't natively sample, it can't sample when placed in another group
either.