Re: [PATCH v0] perf lock contention: skip traceiter functions
From: Anne Macedo
Date: Fri Mar 08 2024 - 15:42:11 EST
Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> writes:
> 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?
>
I can skip trace_contention_begin and trace_contention_end as well.
Question: I have 1409 __traceiter symbols on my kernel build, should we
ignore them all? Or is __traceiter_contention_begin and
__traceiter_contention_end the only ones that concern the lock contention?
cat /proc/kallsyms | grep -P '\b__traceiter*' | wc -l
1409
>
> 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