linux-kernel - Re: ftrace global trace_pipe

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Message-ID: <20190116084702.6d6ce764@gandalf.local.home>
Date:   Wed, 16 Jan 2019 08:47:02 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Claudio <claudio.fontana@...wa.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: ftrace global trace_pipe_raw

On Wed, 16 Jan 2019 09:00:00 +0100
Claudio <claudio.fontana@...wa.com> wrote:

> Indeed the perf event interface would be awesome, if only it would support tracing all processes.
> 
> Unfortunately for my use case, it can only trace one process on any cpus, or all processes on one (1) cpu.
> 
> I guess for some kind of security concerns..

Not security, but performance.

Serialized writes are best done on serialized instances (per cpu or a
single task). Having all tasks on all CPUs write to a single location
is a huge detriment to performance, and has a significant impact. Which
is why the buffer you are asking for doesn't exist.

-- Steve


> 
> I'll take a look at how much work it would be to extend the interface for the any process/any cpu use case.
> 
> Ciao and thank you,
> 
> Claudio
> 
>