From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753180AbeDLOSN (ORCPT ); Thu, 12 Apr 2018 10:18:13 -0400 Received: from foss.arm.com ([217.140.101.70]:33878 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752761AbeDLOSM (ORCPT ); Thu, 12 Apr 2018 10:18:12 -0400 Date: Thu, 12 Apr 2018 15:18:27 +0100 From: Will Deacon To: Waiman Long Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, peterz@infradead.org, mingo@kernel.org, boqun.feng@gmail.com, paulmck@linux.vnet.ibm.com Subject: Re: [PATCH v2 04/13] locking/qspinlock: Remove unbounded cmpxchg loop from locking slowpath Message-ID: <20180412141827.GC21296@arm.com> References: <1523469680-17699-1-git-send-email-will.deacon@arm.com> <1523469680-17699-5-git-send-email-will.deacon@arm.com> <6e6989d0-a6b1-e6fb-4f70-ab6849b715da@redhat.com> <20180412140605.GB21296@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 12, 2018 at 10:16:55AM -0400, Waiman Long wrote: > On 04/12/2018 10:06 AM, Will Deacon wrote: > > On Wed, Apr 11, 2018 at 03:53:16PM -0400, Waiman Long wrote: > >>> diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c > >>> index 396701e8c62d..a8fc402b3f3a 100644 > >>> --- a/kernel/locking/qspinlock.c > >>> +++ b/kernel/locking/qspinlock.c > >>> @@ -162,6 +162,17 @@ struct __qspinlock { > >>> > >>> #if _Q_PENDING_BITS == 8 > >>> /** > >>> + * clear_pending - clear the pending bit. > >>> + * @lock: Pointer to queued spinlock structure > >>> + * > >>> + * *,1,* -> *,0,* > >>> + */ > >>> +static __always_inline void clear_pending(struct qspinlock *lock) > >>> +{ > >>> + WRITE_ONCE(lock->pending, 0); > >>> +} > >>> + > >>> +/** > >>> * clear_pending_set_locked - take ownership and clear the pending bit. > >>> * @lock: Pointer to queued spinlock structure > >>> * > >>> @@ -201,6 +212,17 @@ static __always_inline u32 xchg_tail(struct qspinlock *lock, u32 tail) > >>> #else /* _Q_PENDING_BITS == 8 */ > >>> > >>> /** > >>> + * clear_pending - clear the pending bit. > >>> + * @lock: Pointer to queued spinlock structure > >>> + * > >>> + * *,1,* -> *,0,* > >>> + */ > >>> +static __always_inline void clear_pending(struct qspinlock *lock) > >>> +{ > >>> + atomic_andnot(_Q_PENDING_VAL, &lock->val); > >>> +} > >>> + > >>> +/** > >>> * clear_pending_set_locked - take ownership and clear the pending bit. > >>> * @lock: Pointer to queued spinlock structure > >>> * > >> BTW, there is a similar clear_pending() function in > >> qspinlock_paravirt.c. I think you need to remove that with this patch. > > Thanks, I'll do that. I did build and bisect this series... for arm64, which > > is completely useless as it doesn't get compiled until the final patch which > > I haven't posted here. > > > > Will > > You certainly need to get a x86 system and compiles with the patches > applied one-by-one with CONFIG_PARAVIRT_SPINLOCKS enabled. Yup, doing that now. I just botched my test scripts before, which default to arm64. Will