linux-kernel - Re: [RFC PATCH 1/1] smp: Add tracepoints for functions called with smp_call

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Date:   Thu, 6 Apr 2023 09:49:47 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Leonardo Brás <leobras@...hat.com>
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Yury Norov <yury.norov@...il.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Nadav Amit <namit@...are.com>,
        Zhen Lei <thunder.leizhen@...wei.com>,
        Chen Zhongjin <chenzhongjin@...wei.com>,
        linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: [RFC PATCH 1/1] smp: Add tracepoints for functions called with
 smp_call_function*()

On Thu, 06 Apr 2023 05:42:13 -0300
Leonardo Brás <leobras@...hat.com> wrote:

> Hello Sebastian, thanks for the heads up!
> 
> IIUC Valentin is adding/improving tracepoints that are collected in the
> requesting CPU, at the moment of scheduling the IPI, which are also useful.
> 
> But on my scenario, would be nice to actually have the information on the time
> window in which the requested function is running in the requested CPU. 
> 

Well once you know the functions that are being called (running your test
case with the IPI trace events), then you can get the timings of those same
functions by:

 # cd /sys/kernel/tracing
 # echo '<space-delimited-list-of-functions>' > set_ftrace_filter
 # echo function_graph > current_tracer

Then the function graph will give you those timings.

-- Steve