linux-kernel - Re: [PATCH 1/3] perf/x86: Fix low freq setting issue

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Message-ID: <34d30d5d-da9c-46d0-9477-c25dadf06b42@amd.com>
Date: Mon, 20 Jan 2025 10:30:11 +0530
From: Ravi Bangoria <ravi.bangoria@....com>
To: kan.liang@...ux.intel.com, peterz@...radead.org, mingo@...hat.com,
 acme@...nel.org, namhyung@...nel.org, irogers@...gle.com,
 linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Cc: ak@...ux.intel.com, jolsa@...hat.com, stable@...r.kernel.org,
 Ravi Bangoria <ravi.bangoria@....com>
Subject: Re: [PATCH 1/3] perf/x86: Fix low freq setting issue

On 17-Jan-25 8:49 PM, kan.liang@...ux.intel.com wrote:
> From: Kan Liang <kan.liang@...ux.intel.com>
> 
> Perf doesn't work with a low freq.
> 
> perf record -e cpu_core/instructions/ppp -F 120
> Error:
> The sys_perf_event_open() syscall returned with 22 (Invalid argument)
> for event (cpu_core/instructions/ppp).
> "dmesg | grep -i perf" may provide additional information.
> 
> The limit_period() check avoids a low sampling period on a counter. It
> doesn't intend to limit the frequency.
> The check in the x86_pmu_hw_config() should be limited to non-freq mode.
> The attr.sample_period and attr.sample_freq are union. The
> attr.sample_period should not be used to indicate the freq mode.
> 
> Fixes: c46e665f0377 ("perf/x86: Add INST_RETIRED.ALL workarounds")
> Closes: https://lore.kernel.org/lkml/20250115154949.3147-1-ravi.bangoria@amd.com/
> Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
> Cc: Andi Kleen <ak@...ux.intel.com>
> Cc: Ravi Bangoria <ravi.bangoria@....com>
> Cc: stable@...r.kernel.org

Reviewed-by: Ravi Bangoria <ravi.bangoria@....com>

Thanks,
Ravi