Re: [PATCH v0] perf lock contention: skip traceiter functions

From: Arnaldo Carvalho de Melo
Date: Fri Mar 08 2024 - 14:37:38 EST

On Fri, Mar 08, 2024 at 12:03:31PM +0000, Anne Macedo wrote:
> The perf lock contention program currently shows the caller of the locks
> as __traceiter_contention_begin+0x??. This caller can be ignored, as it is
> from the traceiter itself. Instead, it should show the real callers for
> the locks.
>
> When fiddling with the --stack-skip parameter, the actual callers for
> the locks start to show up. However, just ignore the
> __traceiter_contention_begin and the __traceiter_contention_end symbols
> so the actual callers will show up.
>
> Before this patch is applied:
>
> sudo perf lock con -a -b -- sleep 3
> contended total wait max wait avg wait type caller
>
> 8 2.33 s 2.28 s 291.18 ms rwlock:W __traceiter_contention_begin+0x44
> 4 2.33 s 2.28 s 582.35 ms rwlock:W __traceiter_contention_begin+0x44
> 7 140.30 ms 46.77 ms 20.04 ms rwlock:W __traceiter_contention_begin+0x44
> 2 63.35 ms 33.76 ms 31.68 ms mutex trace_contention_begin+0x84
> 2 46.74 ms 46.73 ms 23.37 ms rwlock:W __traceiter_contention_begin+0x44
> 1 13.54 us 13.54 us 13.54 us mutex trace_contention_begin+0x84
> 1 3.67 us 3.67 us 3.67 us rwsem:R __traceiter_contention_begin+0x44
>
> Before this patch is applied - using --stack-skip 5
>
> sudo perf lock con --stack-skip 5 -a -b -- sleep 3
> contended total wait max wait avg wait type caller
>
> 2 2.24 s 2.24 s 1.12 s rwlock:W do_epoll_wait+0x5a0
> 4 1.65 s 824.21 ms 412.08 ms rwlock:W do_exit+0x338
> 2 824.35 ms 824.29 ms 412.17 ms spinlock get_signal+0x108
> 2 824.14 ms 824.14 ms 412.07 ms rwlock:W release_task+0x68
> 1 25.22 ms 25.22 ms 25.22 ms mutex cgroup_kn_lock_live+0x58
> 1 24.71 us 24.71 us 24.71 us spinlock do_exit+0x44
> 1 22.04 us 22.04 us 22.04 us rwsem:R lock_mm_and_find_vma+0xb0
>
> After this patch is applied:
>
> sudo ./perf lock con -a -b -- sleep 3
> contended total wait max wait avg wait type caller
>
> 6 5.27 s 1.76 s 878.55 ms rwlock:W release_task+0x68
> 2 2.99 s 2.99 s 1.50 s spinlock do_send_sig_info+0x3c
> 2 1.77 s 1.77 s 884.39 ms spinlock sigprocmask+0x98
> 2 1.76 s 1.76 s 878.56 ms rwlock:W do_exit+0x338
> 2 1.76 s 1.76 s 878.55 ms rwlock:W release_task+0x68
> 5 1.76 s 1.76 s 351.41 ms rwlock:W do_exit+0x338
> 1 48.10 ms 48.10 ms 48.10 ms mutex trace_contention_begin+0x84
> 4 257.80 us 119.34 us 64.45 us spinlock get_signal+0x108
> 1 9.33 us 9.33 us 9.33 us rwlock:W do_exit+0x338

Testing it on the ARM64 board sometimes also show that
trace_contention_begin+0x84, maybe we need to skip that one as well?

root@roc-rk3399-pc:~# perf lock contention --use-bpf -a sleep 2
contended total wait max wait avg wait type caller

root@roc-rk3399-pc:~# perf lock contention -b -a find / > /dev/null
contended total wait max wait avg wait type caller

4 4.07 s 2.47 s 1.02 s spinlock cpu_pm_enter+0x34
6 3.43 s 3.43 s 572.20 ms spinlock __tick_broadcast_oneshot_control+0xc0
3 313.19 ms 313.16 ms 104.40 ms spinlock tick_do_update_jiffies64+0x44
6 6.06 ms 1.97 ms 1.01 ms mutex trace_contention_begin+0x84
6 89.25 us 19.25 us 14.88 us spinlock rcu_core+0xec
1 16.04 us 16.04 us 16.04 us spinlock sugov_update_shared+0x44
root@roc-rk3399-pc:~# perf lock contention -b -a find / > /dev/null
contended total wait max wait avg wait type caller

4 2.78 ms 1.09 ms 695.76 us mutex trace_contention_begin+0x84
root@roc-rk3399-pc:~# perf lock contention -b -a find / > /dev/null
contended total wait max wait avg wait type caller

1 389.50 us 389.50 us 389.50 us mutex trace_contention_begin+0x84
root@roc-rk3399-pc:~# perf lock contention -b -a find / > /dev/null
contended total wait max wait avg wait type caller

2 3.82 ms 3.43 ms 1.91 ms mutex trace_contention_begin+0x84
root@roc-rk3399-pc:~# perf lock contention -b -a find / > /dev/null
contended total wait max wait avg wait type caller

3 6.82 ms 2.37 ms 2.27 ms mutex trace_contention_begin+0x84
2 63.29 us 45.50 us 31.65 us mutex trace_contention_begin+0x84
1 52.79 us 52.79 us 52.79 us mutex trace_contention_begin+0x84
root@roc-rk3399-pc:~# perf lock contention -b -a find / > /dev/null
contended total wait max wait avg wait type caller

root@roc-rk3399-pc:~#

> Signed-off-by: Anne Macedo <retpolanne@xxxxxxxxxx>
> ---
> tools/perf/util/machine.c | 10 ++++++++++
> tools/perf/util/machine.h | 2 +-
> 2 files changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
> index 527517db3182..8e729167c1aa 100644
> --- a/tools/perf/util/machine.c
> +++ b/tools/perf/util/machine.c
> @@ -3266,6 +3266,12 @@ bool machine__is_lock_function(struct machine *machine, u64 addr)
>
> sym = machine__find_kernel_symbol_by_name(machine, "__lock_text_end", &kmap);
> machine->lock.text_end = map__unmap_ip(kmap, sym->start);
> +
> + sym = machine__find_kernel_symbol_by_name(machine, "__traceiter_contention_begin", &kmap);
> + machine->traceiter.text_start = map__unmap_ip(kmap, sym->start);
> +
> + sym = machine__find_kernel_symbol_by_name(machine, "__traceiter_contention_end", &kmap);
> + machine->traceiter.text_end = map__unmap_ip(kmap, sym->start);
> }
>
> /* failed to get kernel symbols */
> @@ -3280,5 +3286,9 @@ bool machine__is_lock_function(struct machine *machine, u64 addr)
> if (machine->lock.text_start <= addr && addr < machine->lock.text_end)
> return true;
>
> + /* traceiter functions are in traceiter text section */
> + if (machine->traceiter.text_start <= addr && addr < machine->traceiter.text_end)
> + return true;
> +
> return false;
> }
> diff --git a/tools/perf/util/machine.h b/tools/perf/util/machine.h
> index e28c787616fe..ec51e9b080b9 100644
> --- a/tools/perf/util/machine.h
> +++ b/tools/perf/util/machine.h
> @@ -49,7 +49,7 @@ struct machine {
> struct {
> u64 text_start;
> u64 text_end;
> - } sched, lock;
> + } sched, lock, traceiter;
> pid_t *current_tid;
> size_t current_tid_sz;
> union { /* Tool specific area */
> --
> 2.39.2