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From: Peter Zijlstra <peterz@infradead.org>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>,
	linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
	waiman.long@hp.com
Subject: Re: [PATCH] locking/qrwlock: fix write unlock issue in big endian
Date: Thu, 2 Jun 2016 13:02:00 +0200	[thread overview]
Message-ID: <20160602110200.GZ3190@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <4399273.0kije2Qdx5@wuerfel>

On Thu, Jun 02, 2016 at 12:44:51PM +0200, Arnd Bergmann wrote:
> On Thursday, June 2, 2016 6:09:08 PM CEST Pan Xinhui wrote:
> > diff --git a/include/asm-generic/qrwlock.h b/include/asm-generic/qrwlock.h
> > index 54a8e65..eadd7a3 100644
> > --- a/include/asm-generic/qrwlock.h
> > +++ b/include/asm-generic/qrwlock.h
> > @@ -139,7 +139,7 @@ static inline void queued_read_unlock(struct qrwlock *lock)
> >   */
> >  static inline void queued_write_unlock(struct qrwlock *lock)
> >  {
> > -       smp_store_release((u8 *)&lock->cnts, 0);
> > +       (void)atomic_sub_return_release(_QW_LOCKED, &lock->cnts);
> >  }
> 
> Isn't this more expensive than the existing version?

Yes, loads. And while this might be a suitable fix for asm-generic, it
will introduce a fairly large regression on x86 (which is currently the
only user of this).

  parent reply	other threads:[~2016-06-02 11:02 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-02 10:09 Pan Xinhui
2016-06-02 10:44 ` Arnd Bergmann
2016-06-02 11:01   ` xinhui
2016-06-02 11:15     ` Peter Zijlstra
2016-06-03  7:20       ` xinhui
2016-06-02 11:02   ` Peter Zijlstra [this message]
2016-06-03  7:17     ` xinhui
     [not found]     ` <201606030718.u537FQg0009963@mx0a-001b2d01.pphosted.com>
2016-06-03 20:57       ` Waiman Long
2016-06-06  3:15         ` xinhui
2016-06-08  9:22 ` Will Deacon
2016-06-14  6:11   ` xinhui
2016-06-14 10:40     ` Will Deacon
2016-06-15  3:47       ` xinhui

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