linux-kernel - Re: [PATCH] locking/osq: Drop the overload of osq lock

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Date:	Sat, 25 Jun 2016 18:13:07 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Boqun Feng <boqun.feng@...il.com>
Cc:	Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, mingo@...hat.com, dave@...olabs.net,
	will.deacon@....com, Waiman.Long@....com, benh@...nel.crashing.org
Subject: Re: [PATCH] locking/osq: Drop the overload of osq lock

On Sat, Jun 25, 2016 at 06:09:22PM +0200, Peter Zijlstra wrote:
> That works here, but it would not work for the need_resched() in
> mutex_spin_on_owner() and mutex_optimistic_spin() which need equal
> treatment.
> 
> Because those too we want to limit.
> 
> The count thing, while a little more cumbersome, is more widely
> applicable than just the one OSQ case where we happen to have a cpu
> number.

Although I suppose that mutex_spin_on_owner() (and with that the rsem
variant) could use task_cpu(lock->owner) once we've established that the
owner pointer is still valid.