linux-kernel - Re: [PATCH] tracing: Have synthetic event test use raw_smp_processor

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Message-Id: <20200221192247.1b3f693f3023470b9f8a2068@kernel.org>
Date:   Fri, 21 Feb 2020 19:22:47 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Tom Zanussi <zanussi@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing: Have synthetic event test use
 raw_smp_processor_id()

On Thu, 20 Feb 2020 21:52:36 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Fri, 21 Feb 2020 09:22:30 +0900
> Masami Hiramatsu <mhiramat@...nel.org> wrote:
> 
> > On Thu, 20 Feb 2020 16:14:40 -0600
> > Tom Zanussi <zanussi@...nel.org> wrote:
> > 
> > > Hi Steve,
> > > 
> > > On Thu, 2020-02-20 at 16:29 -0500, Steven Rostedt wrote:  
> > > > From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
> > > > 
> > > > The test code that tests synthetic event creation pushes in as one of
> > > > its
> > > > test fields the current CPU using "smp_processor_id()". As this is
> > > > just
> > > > something to see if the value is correctly passed in, and the actual
> > > > CPU
> > > > used does not matter, use raw_smp_processor_id(), otherwise with
> > > > debug
> > > > preemption enabled, a warning happens as the smp_processor_id() is
> > > > called
> > > > without preemption enabled.
> > > > 
> > > > Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>  
> > > 
> > > Makes sense - I guess it's simpler than Masami's and fine for this
> > > purpose.
> > > 
> > > Reviewed-by: Tom Zanussi <zanussi@...nel.org>  
> > 
> > Hmm, can we reserve ring buffer on CPU1 and commit it on CPU2?
> > Shouldn't we disable preemption between them?
> > 
> 
> I don't think it matters. There's nothing that checks it. And if one
> was concerned about the content of the CPU, one could always enable
> scheduling events and see the task migrate.

Ah, OK I confirmed that the preemption is disabled in ring_buffer_nest_start()
so it should not happen.

Reviewed-by: Masami Hiramatsu <mhiramat@...nel.org>

Thank you!

> 
> -- Steve
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>