linux-kernel - Re: [PATCH v3 08/10] perf/core: Introduce pmu->adjust

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Message-ID: <20241218135229.GE2354@noisy.programming.kicks-ass.net>
Date: Wed, 18 Dec 2024 14:52:29 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Ravi Bangoria <ravi.bangoria@....com>
Cc: mingo@...hat.com, namhyung@...nel.org, acme@...nel.org,
	eranian@...gle.com, mark.rutland@....com,
	alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
	irogers@...gle.com, adrian.hunter@...el.com,
	kan.liang@...ux.intel.com, tglx@...utronix.de, bp@...en8.de,
	dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	santosh.shukla@....com, ananth.narayan@....com,
	sandipan.das@....com
Subject: Re: [PATCH v3 08/10] perf/core: Introduce pmu->adjust_period()
 callback

On Tue, Dec 10, 2024 at 09:34:47AM +0000, Ravi Bangoria wrote:
> Many hardware PMUs have constraints about sample period. For ex, minimum
> supported sample period for IBS Op PMU is 0x90, the sample period must
> be multiple of 0x10 for IBS Fetch and IBS Op.
> 
> Add an optional callback adjust_period() to struct PMU to allow PMU
> specific drivers to adjust sample period calculated by generic code.
> This will ensure the sample_period value will always be valid and no
> additional code is required in PMU specific drivers to re-adjust the
> period.

And not a word about pmu::check_period() and x86_pmu::limit_period() :-(

Please explain why that can't be made to work nor adapted.