Since commit 096b52fd2bb4 ("perf: RISC-V: throttle perf events") the
perf_sample_event_took() function was added to report time spent in
overflow interrupts. If the interrupt takes too long, the perf framework
will lower the sysctl_perf_event_sample_rate and max_samples_per_tick.
When hwc->interrupts is larger than max_samples_per_tick, the
hwc->interrupts will be set to MAX_INTERRUPTS, and events will be
throttled within the __perf_event_account_interrupt() function.
However, the RISC-V PMU driver doesn't call riscv_pmu_stop() to update the
PERF_HES_STOPPED flag after perf_event_overflow() in pmu_sbi_ovf_handler()
function to avoid throttling. When the perf framework unthrottled the event
in the timer interrupt handler, it triggers riscv_pmu_start() function
and causes a WARN_ON_ONCE() warning, as shown below:
------------[ cut here ]------------
WARNING: CPU: 0 PID: 240 at drivers/perf/riscv_pmu.c:184 riscv_pmu_start+0x7c/0x8e
Modules linked in:
CPU: 0 PID: 240 Comm: ls Not tainted 6.4-rc4-g19d0788e9ef2 #1
Hardware name: SiFive (DT)
epc : riscv_pmu_start+0x7c/0x8e
ra : riscv_pmu_start+0x28/0x8e
epc : ffffffff80aef864 ra : ffffffff80aef810 sp : ffff8f80004db6f0
gp : ffffffff81c83750 tp : ffffaf80069f9bc0 t0 : ffff8f80004db6c0
t1 : 0000000000000000 t2 : 000000000000001f s0 : ffff8f80004db720
s1 : ffffaf8008ca1068 a0 : 0000ffffffffffff a1 : 0000000000000000
a2 : 0000000000000001 a3 : 0000000000000870 a4 : 0000000000000000
a5 : 0000000000000000 a6 : 0000000000000840 a7 : 0000000000000030
s2 : 0000000000000000 s3 : ffffaf8005165800 s4 : ffffaf800424da00
s5 : ffffffffffffffff s6 : ffffffff81cc7590 s7 : 0000000000000000
s8 : 0000000000000006 s9 : 0000000000000001 s10: ffffaf807efbc340
s11: ffffaf807efbbf00 t3 : ffffaf8006a16028 t4 : 00000000dbfbb796
t5 : 0000000700000000 t6 : ffffaf8005269870
status: 0000000200000100 badaddr: 0000000000000000 cause: 0000000000000003
[<ffffffff80aef864>] riscv_pmu_start+0x7c/0x8e
[<ffffffff80185b56>] perf_adjust_freq_unthr_context+0x15e/0x174
[<ffffffff80188642>] perf_event_task_tick+0x88/0x9c
[<ffffffff800626a8>] scheduler_tick+0xfe/0x27c
[<ffffffff800b5640>] update_process_times+0x9a/0xba
[<ffffffff800c5bd4>] tick_sched_handle+0x32/0x66
[<ffffffff800c5e0c>] tick_sched_timer+0x64/0xb0
[<ffffffff800b5e50>] __hrtimer_run_queues+0x156/0x2f4
[<ffffffff800b6bdc>] hrtimer_interrupt+0xe2/0x1fe
[<ffffffff80acc9e8>] riscv_timer_interrupt+0x38/0x42
[<ffffffff80090a16>] handle_percpu_devid_irq+0x90/0x1d2
[<ffffffff8008a9f4>] generic_handle_domain_irq+0x28/0x36
After referring other PMU drivers like Arm, Loongarch, Csky, and Mips,
they don't call *_pmu_stop() to update with PERF_HES_STOPPED flag
after perf_event_overflow() function nor do they add PERF_HES_STOPPED
flag checking in *_pmu_start() which don't cause this warning.
Thus, it's recommended to remove this unnecessary check in
riscv_pmu_start() function to prevent this warning.
Signed-off-by: Eric Lin <[email protected]>
---
drivers/perf/riscv_pmu.c | 3 ---
1 file changed, 3 deletions(-)
diff --git a/drivers/perf/riscv_pmu.c b/drivers/perf/riscv_pmu.c
index ebca5eab9c9b..56897d4d4fd3 100644
--- a/drivers/perf/riscv_pmu.c
+++ b/drivers/perf/riscv_pmu.c
@@ -181,9 +181,6 @@ void riscv_pmu_start(struct perf_event *event, int flags)
uint64_t max_period = riscv_pmu_ctr_get_width_mask(event);
u64 init_val;
- if (WARN_ON_ONCE(!(event->hw.state & PERF_HES_STOPPED)))
- return;
-
if (flags & PERF_EF_RELOAD)
WARN_ON_ONCE(!(event->hw.state & PERF_HES_UPTODATE));
--
2.17.1
Hello:
This patch was applied to riscv/linux.git (fixes)
by Palmer Dabbelt <[email protected]>:
On Mon, 10 Jul 2023 15:43:28 +0000 you wrote:
> Since commit 096b52fd2bb4 ("perf: RISC-V: throttle perf events") the
> perf_sample_event_took() function was added to report time spent in
> overflow interrupts. If the interrupt takes too long, the perf framework
> will lower the sysctl_perf_event_sample_rate and max_samples_per_tick.
> When hwc->interrupts is larger than max_samples_per_tick, the
> hwc->interrupts will be set to MAX_INTERRUPTS, and events will be
> throttled within the __perf_event_account_interrupt() function.
>
> [...]
Here is the summary with links:
- perf: RISC-V: Remove PERF_HES_STOPPED flag checking in riscv_pmu_start()
https://git.kernel.org/riscv/c/66843b14fb71
You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html
On Mon, 10 Jul 2023 15:43:28 +0000, Eric Lin wrote:
> Since commit 096b52fd2bb4 ("perf: RISC-V: throttle perf events") the
> perf_sample_event_took() function was added to report time spent in
> overflow interrupts. If the interrupt takes too long, the perf framework
> will lower the sysctl_perf_event_sample_rate and max_samples_per_tick.
> When hwc->interrupts is larger than max_samples_per_tick, the
> hwc->interrupts will be set to MAX_INTERRUPTS, and events will be
> throttled within the __perf_event_account_interrupt() function.
>
> [...]
Applied, thanks!
[1/1] perf: RISC-V: Remove PERF_HES_STOPPED flag checking in riscv_pmu_start()
https://git.kernel.org/palmer/c/66843b14fb71
Best regards,
--
Palmer Dabbelt <[email protected]>