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

[Arnaldo Carvalho de Melo <acme@kernel.org>]

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@posteo.net>
> ---
>  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