linux-kernel - Re: [PATCH 2/2] sched/debug: fix deadlock when enabling sched events

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Date:	Wed, 8 Jun 2016 09:13:05 +0100
From:	Mel Gorman <mgorman@...hsingularity.net>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Josh Poimboeuf <jpoimboe@...hat.com>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Matt Fleming <matt@...eblueprint.co.uk>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Subject: Re: [PATCH 2/2] sched/debug: fix deadlock when enabling sched events

On Tue, Jun 07, 2016 at 09:54:48PM +0200, Peter Zijlstra wrote:
> On Tue, Jun 07, 2016 at 02:43:17PM -0500, Josh Poimboeuf wrote:
> > 1. Instead of just warning and allowing the tracepoints to be broken,
> >    I'd argue that it would be better to make them work by forcing
> >    schedstats enabled and printing a warning about that, which is what's
> 
> Forcing them enabled doesn't make them useful per se; some of these
> tracepoint rely on previously recoded state, which now wasn't previously
> recorded because back then it was disabled.
> 

This is unfortunately true. It means there is a window when the data is
unreliable after the stats are enabled. It is assumed that either someone
enabling the stats knows that or is willing to enable them on the command
line.

-- 
Mel Gorman
SUSE Labs