Re: [PATCH v1] perf lock contention: skip traceiter functions

Anne Macedo
2024-03-11T18:44:32Z

Namhyung Kim <namhyung@kernel.org> writes:

> Hello Anne,
>
> On Sat, Mar 9, 2024 at 5:27 AM Anne Macedo <retpolanne@posteo.net> 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
>>
>> 4 4.13 s 2.07 s 1.03 s rwlock:W release_task+0x68
>> 2 2.07 s 2.07 s 1.03 s rwlock:R mm_update_next_owner+0x50
>> 2 2.07 s 2.07 s 1.03 s rwlock:W do_exit+0x338
>> 1 41.56 ms 41.56 ms 41.56 ms mutex cgroup_kn_lock_live+0x58
>> 2 36.12 us 18.83 us 18.06 us rwlock:W do_exit+0x338
>>
>> changes since v0:
>>
>> - skip trace_contention functions
>> - use sym->end instead of __traceiter_contention_end for text_end
>>
>> Signed-off-by: Anne Macedo <retpolanne@posteo.net>
>> ---
>> tools/perf/util/machine.c | 17 +++++++++++++++++
>> tools/perf/util/machine.h | 2 +-
>> 2 files changed, 18 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
>> index 527517db3182..db443947ccd1 100644
>> --- a/tools/perf/util/machine.c
>> +++ b/tools/perf/util/machine.c
>> @@ -3266,6 +3266,14 @@ 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);
>
> Unlike __sched_text_{start,end} and __lock_text_{start,end} I guess
> this traceiter thing is optional so it might not be there. You need to
> handle if it's NULL.
>

Let me test with CONFIG_TRACEPOINTS=n then.

> I think it depends on the kernel version and configuration. I remember
> I saw a different symbol on old kernels. But it'd be hard to handle all
> the cases. Let's have a single trace text section in the struct machine
> and use __traceiter_contention_begin only. If it's not found you can
> fallback to trace_contention_begin.
>
ACK :)
>
> Thanks,
> Namhyung
>
>
>> + machine->traceiter.text_start = map__unmap_ip(kmap, sym->start);
>> + machine->traceiter.text_end = map__unmap_ip(kmap, sym->end);
>> +
>> + sym = machine__find_kernel_symbol_by_name(machine, "trace_contention_begin", &kmap);
>> + machine->trace.text_start = map__unmap_ip(kmap, sym->start);
>> + machine->trace.text_end = map__unmap_ip(kmap, sym->end);
>> }
>>
>> /* failed to get kernel symbols */
>> @@ -3280,5 +3288,14 @@ 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 currently don't have their own section
>> + * but we consider them lock functions
>> + */
>> + if (machine->traceiter.text_start <= addr && addr < machine->traceiter.text_end)
>> + return true;
>> +
>> + if (machine->trace.text_start <= addr && addr < machine->trace.text_end)
>> + return true;
>> +
>> return false;
>> }
>> diff --git a/tools/perf/util/machine.h b/tools/perf/util/machine.h
>> index e28c787616fe..4312f6db6de0 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, trace;
>> pid_t *current_tid;
>> size_t current_tid_sz;
>> union { /* Tool specific area */
>> --
>> 2.39.2
>>