From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751247AbcGNJhv (ORCPT ); Thu, 14 Jul 2016 05:37:51 -0400 Received: from merlin.infradead.org ([205.233.59.134]:45869 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750957AbcGNJhm (ORCPT ); Thu, 14 Jul 2016 05:37:42 -0400 Date: Thu, 14 Jul 2016 11:37:33 +0200 From: Peter Zijlstra To: xinhui Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, mingo@redhat.com, arnd@arndb.de, Waiman.Long@hpe.com Subject: Re: [PATCH v3] locking/qrwlock: Let qrwlock has same layout regardless of the endian Message-ID: <20160714093733.GF30909@twins.programming.kicks-ass.net> References: <1466403652-2931-1-git-send-email-xinhui.pan@linux.vnet.ibm.com> <20160713195423.GD30921@twins.programming.kicks-ass.net> <578742EA.7060108@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <578742EA.7060108@linux.vnet.ibm.com> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 14, 2016 at 03:44:42PM +0800, xinhui wrote: > >OK, so I poked at this a bit and I ended up with the below; but now > >qrwlock and qspinlock are inconsistent; although I suspect qspinlock is > >similarly busted wrt endian muck. > > > >Not sure what to do.. > > > Lets talk about the qspinlock. > > for x86, We has already assumed that ->locked sit at the low 8 bits, as is > smp_store_release((u8 *)lock, 0); Right, true on x86 though :-) I noticed your PPC patches have a +3 in there conditional on __BIG_ENDIAN. > Then we can do a favor, export ->locked but other fields as reserved. > say > > struct __qspinlock_unlcok_interface {/* what name is better?*/ > #ifdef __LITTLE_ENDIAN > u8 locked; > u8 reserved[3]; /* do not touch it, internally use only */ > #else > u8 reserved[3]; > u8 locked; > #endif > }; Right, maybe, although something like: static inline u8 *__qspinlock_lock_byte(struct qspinlock *lock) { return (u8 *)lock + 3 * IS_BUILTIN(__BIG_ENDIAN); } static inline u8 *__qrwlock_write_byte(struct qrwlock *lock) { return (u8 *)lock + 3 * IS_BUILTIN(__BIG_ENDIAN); } is shorter? > > /* > >+ * Writer states & reader shift and bias. > >+ * > >+ * | +0 | +1 | +2 | +3 | > >+ * ----+----+----+----+----+ > >+ * LE | 12 | 34 | 56 | 78 | 0x12345678 > >+ * ----+----+----+----+----+ > >+ * BE | 78 | 56 | 34 | 12 | 0x12345678 > >+ * ----+----+----+----+----+ > >+ * | wr | rd | > >+ * +----+----+----+----+ > >+ * > > */ > > very clearly. :) I did one for the qspinlock code too.. diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index b2caec7315af..9191dc454e96 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -120,6 +120,23 @@ static inline __pure struct mcs_spinlock *decode_tail(u32 tail) * * This internal structure is also used by the set_locked function which * is not restricted to _Q_PENDING_BITS == 8. + * + * | +0 | +1 | +2 | +3 | + * ----+----+----+----+----+ + * LE | 78 | 56 | 34 | 12 | val = 0x12345678 + * ----+----+----+----+----+ + * LE | 34 | 12 | locked_pending = 0x1234 + * ----+----+----+----+----+ + * | L | P | tail | + * +----+----+----+----+ + * + * ----+----+----+----+----+ + * BE | 12 | 34 | 56 | 78 | val = 0x12345678 + * ----+----+----+----+----+ + * BE | 12 | 34 | locked_pending = 0x1234 + * ----+----+----+----+----+ + * | tail | P | L | + * +----+----+----+----+ */ struct __qspinlock { union {