linux-kernel - Re: [RFC][PATCH 12/13] stop

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Message-ID: <20150624175830.GS3644@twins.programming.kicks-ass.net>
Date:	Wed, 24 Jun 2015 19:58:30 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, tj@...nel.org, mingo@...hat.com,
	linux-kernel@...r.kernel.org, der.herr@...r.at, dave@...olabs.net,
	riel@...hat.com, viro@...IV.linux.org.uk,
	torvalds@...ux-foundation.org
Subject: Re: [RFC][PATCH 12/13] stop_machine: Remove lglock

On Wed, Jun 24, 2015 at 10:10:17AM -0700, Paul E. McKenney wrote:
> > The thing is, once you start bailing on this condition your 'queue'
> > drains very fast and this is around the same time sync_rcu() would've
> > released the waiters too.
> 
> In my experience, this sort of thing simply melts down on large systems.
> I am reworking this with multiple locks so as to keep the large-system
> contention down to a dull roar.

So with the MCS queue we're got less global trashing than you had with
the start/done tickets. Only the queue head on enqueue.

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