linux-kernel - Re: [PATCH RFC 0/2] Add basic tracing support for m68k

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Message-ID: <cbb67ee2-8b37-4a4d-b542-f89ddae90e94@yoseli.org>
Date: Fri, 15 Nov 2024 16:33:06 +0100
From: Jean-Michel Hautbois <jeanmichel.hautbois@...eli.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-m68k@...ts.linux-m68k.org, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, Geert Uytterhoeven
 <geert@...ux-m68k.org>, Greg Ungerer <gerg@...ux-m68k.org>
Subject: Re: [PATCH RFC 0/2] Add basic tracing support for m68k

Hi Steve,

On 15/11/2024 16:25, Steven Rostedt wrote:
> On Fri, 15 Nov 2024 09:26:07 +0100
> Jean-Michel Hautbois <jeanmichel.hautbois@...eli.org> wrote:
> 
>> Nevertheless it sounds like a really high latency for wake_up().
>>
>> I have a custom driver which basically gets an IRQ, and calls wake_up on
>> a read() call. This wake_up() on a high cpu usage can be more than 1ms !
>> Even with a fifo/99 priority for my kernel thread !
>>
>> I don't know if it rings any bell ?
>> I can obviously do more tests if it can help getting down to the issue :-).
> 
> Try running timerlat.

Thanks !
Here is what I get:
# echo timerlat > current_tracer
# echo 1 > events/osnoise/enable
# echo 25 > osnoise/stop_tracing_total_us
# tail -10 trace
             bash-224     [000] d.h..   153.268917: #77645 context 
irq timer_latency     45056 ns
             bash-224     [000] dnh..   153.268987: irq_noise: timer:206 
start 153.268879083 duration 93957 ns
             bash-224     [000] d....   153.269056: thread_noise: 
bash:224 start 153.268905324 duration 71045 ns
       timerlat/0-271     [000] .....   153.269103: #77645 context 
thread timer_latency    230656 ns
             bash-224     [000] d.h..   153.269735: irq_noise: timer:206 
start 153.269613847 duration 103558 ns
             bash-224     [000] d.h..   153.269911: #77646 context 
irq timer_latency     40640 ns
             bash-224     [000] dnh..   153.269982: irq_noise: timer:206 
start 153.269875367 duration 93190 ns
             bash-224     [000] d....   153.270053: thread_noise: 
bash:224 start 153.269900969 duration 72709 ns
       timerlat/0-271     [000] .....   153.270100: #77646 context 
thread timer_latency    227008 ns
       timerlat/0-271     [000] .....   153.270155: timerlat_main: stop 
tracing hit on cpu 0

It looks awful, right ?
JM