linux-kernel - Re: [PATCH 1/2] tracing: show size of requested buffer

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Date:   Thu, 7 Oct 2021 09:11:51 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     "Robin H. Johnson" <robbat2@...too.org>,
        linux-kernel@...r.kernel.org, mingo@...hat.com,
        rjohnson@...italocean.com,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: Re: [PATCH 1/2] tracing: show size of requested buffer

On Tue, Sep 07, 2021 at 09:24:26PM -0400, Steven Rostedt wrote:
> 
> I'll need Acks for these patches from the Perf maintainers.
> 
> -- Steve
> 
> 
> On Mon, 30 Aug 2021 21:37:22 -0700
> "Robin H. Johnson" <robbat2@...too.org> wrote:
> 
> > If the perf buffer isn't large enough, provide a hint about how large it
> > needs to be for whatever is running.

Is that an actual reason?

> > Signed-off-by: Robin H. Johnson <robbat2@...too.org>
> > ---
> >  kernel/trace/trace_event_perf.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
> > index 03be4435d103..26eed4b89100 100644
> > --- a/kernel/trace/trace_event_perf.c
> > +++ b/kernel/trace/trace_event_perf.c
> > @@ -400,7 +400,8 @@ void *perf_trace_buf_alloc(int size, struct pt_regs **regs, int *rctxp)
> >  	BUILD_BUG_ON(PERF_MAX_TRACE_SIZE % sizeof(unsigned long));
> >  
> >  	if (WARN_ONCE(size > PERF_MAX_TRACE_SIZE,
> > -		      "perf buffer not large enough"))
> > +		      "perf buffer not large enough, wanted %d, have %d",
> > +		      size, PERF_MAX_TRACE_SIZE))

Priting a constant seems daft.. why is any of this important in any way?