linux-kernel - Re: [PATCH] sched: Do not release current rq lock on non contended double_lock

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Message-ID: <20160615121353.7194c68b@grimm.local.home>
Date:	Wed, 15 Jun 2016 12:13:53 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Clark Williams <williams@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <nickpiggin@...oo.com.au>
Subject: Re: [PATCH] sched: Do not release current rq lock on non contended
 double_lock_balance()

On Wed, 15 Jun 2016 13:14:53 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> OK, so should not the whole HAVE_RT_PUSH_IPI thing have avoided that
> loop entirely? And therefore made the point moot?

I believe there was another issue that we had in our tests. But I don't
have the trace available with me. I'll rerun the tests when I get back
home and have some more concrete examples for you.

> 
> In any case, can't we add another cpupri for pushable tasks and use that
> to find the highest priority task to pull and avoid the loop thus?

I thought about this too, but I was a bit concerned about complexities
this would add. But I can look into it. Currently I'm in NYC for
personal reasons and will take a look at this when I get back.

-- Steve