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Date:   Wed, 16 Jan 2019 08:47:02 -0500
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Claudio <claudio.fontana@gliwa.com>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-kernel@vger.kernel.org
Subject: Re: ftrace global trace_pipe_raw
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On Wed, 16 Jan 2019 09:00:00 +0100
Claudio <claudio.fontana@gliwa.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
> 
>