linux-kernel - Re: [RFC PATCH v2 0/5] Additional scheduling information in tracepoints

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Message-ID: <20160926122712.GM5012@twins.programming.kicks-ass.net>
Date:   Mon, 26 Sep 2016 14:27:12 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Julien Desfossez <jdesfossez@...icios.com>
Cc:     tglx@...utronix.de, rostedt@...dmis.org, mingo@...hat.com,
        daolivei@...hat.com, mathieu.desnoyers@...icios.com,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 0/5] Additional scheduling information in
 tracepoints

On Fri, Sep 23, 2016 at 12:49:30PM -0400, Julien Desfossez wrote:
> With this macro, we propose new versions of the sched_switch, sched_waking,
> sched_process_fork and sched_pi_setprio tracepoint probes that contain more
> scheduling information and get rid of the "prio" field. We also add the PI
> information to these tracepoints, so if a process is currently boosted, we show
> the name and PID of the top waiter. This allows to quickly see the blocking
> chain even if some of the trace background is missing.

Urgh.. bigger mess than ever :-(

So I thought the initial idea was to provide a 'blocked-on' tracepoint,
along with with the 'prio-changed' tracepoint, so you can reconstruct
the entire PI chain.

The only problem with that was initial state; when you start tracing (or
miss the start of a trace) its hard (impossible) to know what the
current state is.

But now you send a patch-set that just adds a metric ton of tracepoints.

This doesn't fix the current mess, it makes it worse :-(