From: Matt Ochs <mochs@nvidia.com>
To: Besar Wicaksono <bwicaksono@nvidia.com>
Cc: "will@kernel.org" <will@kernel.org>,
"mark.rutland@arm.com" <mark.rutland@arm.com>,
"james.clark@linaro.org" <james.clark@linaro.org>,
"yangyccccc@gmail.com" <yangyccccc@gmail.com>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>,
Thierry Reding <treding@nvidia.com>,
Jon Hunter <jonathanh@nvidia.com>,
Vikram Sethi <vsethi@nvidia.com>, Rich Wiley <rwiley@nvidia.com>,
Shanker Donthineni <sdonthineni@nvidia.com>,
Nirmoy Das <nirmoyd@nvidia.com>, Sean Kelley <skelley@nvidia.com>
Subject: Re: [PATCH v3] perf/arm_pmu: Skip PMCCNTR_EL0 on NVIDIA Olympus
Date: Fri, 1 May 2026 00:27:18 +0000 [thread overview]
Message-ID: <4BC7B5BD-9160-4A6A-B18F-E788CF340E8A@nvidia.com> (raw)
In-Reply-To: <20260429215614.1793131-1-bwicaksono@nvidia.com>
> On Apr 29, 2026, at 16:56, Besar Wicaksono <bwicaksono@nvidia.com> wrote:
>
> PMCCNTR_EL0 may continue to increment on NVIDIA Olympus CPUs while the
> PE is in WFI/WFE. That does not necessarily match the CPU_CYCLES event
> counted by a programmable counter, so using PMCCNTR_EL0 for cycles can
> give results that differ from the programmable counter path.
>
> Extend the existing PMCCNTR avoidance decision from the SMT case to
> also cover Olympus. Store the result in the common arm_pmu state at
> registration time, so arm_pmuv3 can keep using a single flag when
> deciding whether CPU_CYCLES may use PMCCNTR_EL0.
>
> Use the cached MIDR from cpu_data to identify Olympus parts and avoid
> reading MIDR_EL1 in the event path.
>
> Signed-off-by: Besar Wicaksono <bwicaksono@nvidia.com>
Verified on NVIDIA Vera (Olympus CPUs) with UEFI SMT disabled. Confirmed
that grouped cpu_cycles events show ~1x ratio (both on programmable
counters) with the patch vs ~15x inflation without it.
Tested-by: Matthew R. Ochs <mochs@nvidia.com>
next prev parent reply other threads:[~2026-05-01 0:27 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-29 21:56 [PATCH v3] perf/arm_pmu: Skip PMCCNTR_EL0 on NVIDIA Olympus Besar Wicaksono
2026-05-01 0:27 ` Matt Ochs [this message]
2026-05-01 14:01 ` James Clark
2026-05-01 21:25 ` Besar Wicaksono
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