linux-kernel - Re: [Patch v3 12/22] perf/x86/intel: Update dyn_constranit base on PEBS event precise level

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Message-ID: <20250416195610.GC38216@noisy.programming.kicks-ass.net>
Date: Wed, 16 Apr 2025 21:56:10 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: "Liang, Kan" <kan.liang@...ux.intel.com>
Cc: Dapeng Mi <dapeng1.mi@...ux.intel.com>, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>, Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Eranian Stephane <eranian@...gle.com>, linux-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org, Dapeng Mi <dapeng1.mi@...el.com>
Subject: Re: [Patch v3 12/22] perf/x86/intel: Update dyn_constranit base on
 PEBS event precise level

On Wed, Apr 16, 2025 at 03:45:24PM -0400, Liang, Kan wrote:

> I see. I think we can check the constraint table and update the overlap
> bit accordingly. Similar to what we did in the
> intel_pmu_check_event_constraints() for the fixed counters.
> 
> I'm thinking something as below (Just a POC, not tested.)

I'll try and digest in more detail tomorrow, but having overlap it *not*
a good thing. Which is why I've always asked to make sure this
doesn't happen :/

At the very least we should WARN if we find the dynamic constraint gets
us there.