linux-kernel - [tip: perf/urgent] perf/x86: Fix low freqency setting issue

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Message-ID: <174049289790.10177.11456494248824677937.tip-bot2@tip-bot2>
Date: Tue, 25 Feb 2025 14:14:57 -0000
From: "tip-bot2 for Kan Liang" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Kan Liang <kan.liang@...ux.intel.com>, Ingo Molnar <mingo@...nel.org>,
 Ravi Bangoria <ravi.bangoria@....com>, Peter Zijlstra <peterz@...radead.org>,
 stable@...r.kernel.org, x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: perf/urgent] perf/x86: Fix low freqency setting issue

The following commit has been merged into the perf/urgent branch of tip:

Commit-ID:     88ec7eedbbd21cad38707620ad6c48a4e9a87c18
Gitweb:        https://git.kernel.org/tip/88ec7eedbbd21cad38707620ad6c48a4e9a87c18
Author:        Kan Liang <kan.liang@...ux.intel.com>
AuthorDate:    Fri, 17 Jan 2025 07:19:11 -08:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Tue, 25 Feb 2025 14:54:14 +01:00

perf/x86: Fix low freqency setting issue

Perf doesn't work at low frequencies:

  $ 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 frequency mode.

Fixes: c46e665f0377 ("perf/x86: Add INST_RETIRED.ALL workarounds")
Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Reviewed-by: Ravi Bangoria <ravi.bangoria@....com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: stable@...r.kernel.org
Link: https://lore.kernel.org/r/20250117151913.3043942-1-kan.liang@linux.intel.com
Closes: https://lore.kernel.org/lkml/20250115154949.3147-1-ravi.bangoria@amd.com/
---
 arch/x86/events/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 8f218ac..2092d61 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -628,7 +628,7 @@ int x86_pmu_hw_config(struct perf_event *event)
 	if (event->attr.type == event->pmu->type)
 		event->hw.config |= x86_pmu_get_event_config(event);
 
-	if (event->attr.sample_period && x86_pmu.limit_period) {
+	if (!event->attr.freq && x86_pmu.limit_period) {
 		s64 left = event->attr.sample_period;
 		x86_pmu.limit_period(event, &left);
 		if (left > event->attr.sample_period)