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

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Date:	Wed, 24 Jun 2015 17:40:10 +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 08:27:19AM -0700, Paul E. McKenney wrote:
> > The thing is, if we're stalled on a stop_one_cpu() call, the sync_rcu()
> > is equally stalled. The sync_rcu() cannot wait more efficient than we're
> > already waiting either.
> 
> Ah, but synchronize_rcu() doesn't force waiting on more than one extra
> grace period.  With strictly queued mutex, you can end up waiting on
> several.

But you could fix that by replacing/augmenting the expedited ticket with
gpnum/copmleted as used in get_state_synchronize_rcu()/cond_synchronize_rcu().


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