From: Kan Liang kan.liang@linux.intel.com

A low freq cannot be set via IOC_PERIOD on some platforms.

The perf_event_check_period() introduced in commit 81ec3f3c4c4d ("perf/x86: Add check_period PMU callback") intended to check the period, rather than the freq. A low freq may be mistakenly rejected by the limit_period().

Fixes: 81ec3f3c4c4d ("perf/x86: Add check_period PMU callback") Closes: https://lore.kernel.org/lkml/20250115154949.3147-1-ravi.bangoria@amd.com/ Signed-off-by: Kan Liang kan.liang@linux.intel.com Cc: Jiri Olsa jolsa@redhat.com Cc: Ravi Bangoria ravi.bangoria@amd.com Cc: stable@vger.kernel.org --- kernel/events/core.c | 17 +++++++++-------- 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c index f91ba29048ce..a9a04d4f3619 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -5960,14 +5960,15 @@ static int _perf_event_period(struct perf_event *event, u64 value) if (!value) return -EINVAL;

- if (event->attr.freq && value > sysctl_perf_event_sample_rate) - return -EINVAL; - - if (perf_event_check_period(event, value)) - return -EINVAL; - - if (!event->attr.freq && (value & (1ULL << 63))) - return -EINVAL; + if (event->attr.freq) { + if (value > sysctl_perf_event_sample_rate) + return -EINVAL; + } else { + if (perf_event_check_period(event, value)) + return -EINVAL; + if (value & (1ULL << 63)) + return -EINVAL; + }

event_function_call(event, __perf_event_period, &value);

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@linux.intel.com AuthorDate: Fri, 17 Jan 2025 07:19:11 -08:00 Committer: Ingo Molnar mingo@kernel.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@linux.intel.com Signed-off-by: Ingo Molnar mingo@kernel.org Reviewed-by: Ravi Bangoria ravi.bangoria@amd.com Cc: Peter Zijlstra peterz@infradead.org Cc: stable@vger.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)