linux-kernel - Re: [PATCH V5] arm64: perf: Make exporting of pmu events configurable

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Date:   Thu, 9 Jun 2022 18:37:34 +0530
From:   Srinivasarao Pathipati <quic_c_spathi@...cinc.com>
To:     Will Deacon <will@...nel.org>
CC:     <mark.rutland@....com>, <peterz@...radead.org>, <mingo@...hat.com>,
        <acme@...nel.org>, <alexander.shishkin@...ux.intel.com>,
        <jolsa@...nel.org>, <namhyung@...nel.org>,
        <catalin.marinas@....com>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-perf-users@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V5] arm64: perf: Make exporting of pmu events configurable


On 6/9/2022 5:02 PM, Will Deacon wrote:
> [Please don't top-post]
>
> On Thu, Jun 09, 2022 at 04:05:20PM +0530, Srinivasarao Pathipati wrote:
>> On 6/9/2022 3:32 PM, Will Deacon wrote:
>>> On Mon, May 23, 2022 at 05:19:34PM +0530, Srinivasarao Pathipati wrote:
>>>> The PMU export bit (PMCR_EL0.X) is getting reset during pmu reset,
>>>> Make is configurable using sysctls to enable/disable at runtime.
>>>> It can also be enabled at early bootup with kernel arguments.
>>>>
>>>> Signed-off-by: Srinivasarao Pathipati <quic_c_spathi@...cinc.com>
>>>> ---
>>>> Changes since V4:
>>>> 	- Registering sysctls dynamically for only arm64 as suggested by Will
>>>> 	- Not removed the code to configure with kernel parameters
>>>> 	  as the sysctl's kernel parameter(sysctl.kernel.export_pmu_events)
>>>> 	  is not working at early bootup. pmu_reset() getting called before
>>>> 	  sysctl's kernel parameter is set.
>>> Why do you need this during early bootup? Perf won't program any events
>>> until much later and if somebody else is configuring the PMU before
>>> entering Linux then they can also set that X bit in the PMCR.
>> On our Qualcomm platforms, The X bit is getting set by firmware at early
>> bootup for Qualcomm use cases
>> and non-secure world is resetting it, that causing issue.
> What "Qualcomm use cases" and why should we care about them upstream?

Thanks Will & Robin for your inputs .

Understood your point ,  pushed next version [V6] after removing kernel 
parameters code.

>
> Will