linux-kernel - Re: Will smp_call_function_single(cpu, ...) broadcast IPI to all other cpus?

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Message-ID: <CAJNi4rMeDgDJbN0jjPguU_v5uoscJJN=5bZaShXpu7Q8X60hcg@mail.gmail.com>
Date: Fri, 28 Jun 2024 18:21:25 +0800
From: richard clark <richard.xnu.clark@...il.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Marc Zyngier <maz@...nel.org>, Mark Rutland <mark.rutland@....com>, will@...nel.org, 
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	"Russell King (Oracle)" <linux@...linux.org.uk>, Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: Will smp_call_function_single(cpu, ...) broadcast IPI to all
 other cpus?

Hi Steven,

On Thu, Jun 27, 2024 at 10:12 PM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Thu, 27 Jun 2024 11:38:58 +0100
> Marc Zyngier <maz@...nel.org> wrote:
>
> > You may want to enable stack trace recording and find out for yourself
> > where these ipi_raise() calls are coming from.
>
> Try trace-cmd:
>
>   # trace-cmd start -e ipi_raise -R 'stacktrace if reason=="Function call interrupts"'
>   # taskset -c 0 insmod /kmods/ipi_test.ko
>   # trace-cmd stop
>   # trace-cmd show
>
I found that the 'stacktrace' seems like a stick bit. Run the above
'# trace-cmd start -e ipi_raise -R 'stacktrace if reason=="Function
call interrupts"' ... command sequence, then
# trace-cmd start -e ipi -f 'reason=="Function call interrupts"' -v -e
ipi_exit; taskset -c 0 insmod /kmods/ipi_lat.ko; trace-cmd stop;
trace-cmd show; trace-cmd clear;
The output is:

          insmod-1746    [000] dn.h1..   928.400039: ipi_raise:
target_mask=00000000,000000ffe (Function call interrupts)
          insmod-1746    [000] dn.h2..   928.400042: <stack trace>
 => trace_event_raw_event_ipi_raise
 => smp_cross_call
 => arch_send_call_function_single_ipi
 => send_call_function_single_ipi
...
Actually, the behavior hoped like this(no stacktrace):

          insmod-1677    [000] ....1..   473.474846: ipi_raise:
target_mask=00000000,00000ffe (Function call interrupts)
          <idle>-0       [002] d..h1..   473.474848: ipi_entry:
(Function call interrupts)
          <idle>-0       [003] d..h1..   473.474849: ipi_entry:
(Function call interrupts)
          ...
          insmod-1677    [000] ....1..   473.474859: ipi_raise:
target_mask=00000000,00000ffe (Function call interrupts)
          <idle>-0       [001] d..h1..   473.474861: ipi_entry:
(Function call interrupts) magic=0x55aa55aa
          ...

I tried to add '# trace-cmd stack --stop/reset' before the above
command, but it did not work. Any help to disable the 'stacktrace' in
this scenario?

> -- Steve