This is a note to let you know that I've just added the patch titled
perf: RISC-V: Remove PERF_HES_STOPPED flag checking in riscv_pmu_start()
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
perf-risc-v-remove-perf_hes_stopped-flag-checking-in-riscv_pmu_start.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 66843b14fb71825fdd73ab12f6594f2243b402be Mon Sep 17 00:00:00 2001
From: Eric Lin <eric.lin@xxxxxxxxxx>
Date: Mon, 10 Jul 2023 15:43:28 +0000
Subject: perf: RISC-V: Remove PERF_HES_STOPPED flag checking in riscv_pmu_start()
From: Eric Lin <eric.lin@xxxxxxxxxx>
commit 66843b14fb71825fdd73ab12f6594f2243b402be upstream.
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 <eric.lin@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20230710154328.19574-1-eric.lin@xxxxxxxxxx
Fixes: 096b52fd2bb4 ("perf: RISC-V: throttle perf events")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Palmer Dabbelt <palmer@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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));
--
2.41.0
Patches currently in stable-queue which might be from eric.lin@xxxxxxxxxx are
queue-6.1/perf-risc-v-remove-perf_hes_stopped-flag-checking-in-riscv_pmu_start.patch
