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

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Date: Fri, 28 Jun 2024 08:41:37 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: richard clark <richard.xnu.clark@...il.com>
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?

On Fri, 28 Jun 2024 18:21:25 +0800
richard clark <richard.xnu.clark@...il.com> wrote:

> 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?

 trace-cmd reset

will put everything back. But yeah, I need to fix it so that it's easier to
reset triggers.

-- Steve