linux-kernel - Re: [PATCH 1/2] kthread: add barriers to set_kthread_struct() and to

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Message-ID: <20170316161429.xaut44wpycty7di4@hirez.programming.kicks-ass.net>
Date:   Thu, 16 Mar 2017 17:14:29 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     Oleg Nesterov <oleg@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>, Chris Mason <clm@...com>,
        linux-kernel@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH 1/2] kthread: add barriers to set_kthread_struct() and
 to_kthread()

On Thu, Mar 16, 2017 at 12:09:44PM -0400, Tejun Heo wrote:
> On Thu, Mar 16, 2017 at 04:55:34PM +0100, Peter Zijlstra wrote:
> > > Oops, as for adding lockless_assign_pointer(), wouldn't smp_wmb() be a
> > > better match for smp_read_barrier_depends()?  ISTR acquire/release
> > > pairs being more expensive on some archs.
> > 
> > 88c1863066cc ("rcu: Define rcu_assign_pointer() in terms of smp_store_release()")
> 
> Hmmm, nice, can we always prefer store_release over wmb from now on?

I would advocate using whichever barrier is most natural for the
occasion.

Only if there really is a very very compelling performance argument
should we look further.