From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/7434 Path: news.gmane.org!not-for-mail From: Alexander Monakov Newsgroups: gmane.linux.lib.musl.general Subject: Re: [PATCH] Use CAS instead of atomic swap to implement spinlock Date: Sun, 19 Apr 2015 08:50:18 +0300 (MSK) Message-ID: References: <1429051493-2821-1-git-send-email-amonakov@ispras.ru> <20150419002433.GL6817@brightrain.aerifal.cx> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Trace: ger.gmane.org 1429422635 3655 80.91.229.3 (19 Apr 2015 05:50:35 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sun, 19 Apr 2015 05:50:35 +0000 (UTC) To: musl@lists.openwall.com Original-X-From: musl-return-7447-gllmg-musl=m.gmane.org@lists.openwall.com Sun Apr 19 07:50:34 2015 Return-path: Envelope-to: gllmg-musl@m.gmane.org Original-Received: from mother.openwall.net ([195.42.179.200]) by plane.gmane.org with smtp (Exim 4.69) (envelope-from ) id 1Yji7k-0003yY-1j for gllmg-musl@m.gmane.org; Sun, 19 Apr 2015 07:50:32 +0200 Original-Received: (qmail 3538 invoked by uid 550); 19 Apr 2015 05:50:30 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: Original-Received: (qmail 3520 invoked from network); 19 Apr 2015 05:50:30 -0000 In-Reply-To: <20150419002433.GL6817@brightrain.aerifal.cx> User-Agent: Alpine 2.11 (LNX 23 2013-08-11) Xref: news.gmane.org gmane.linux.lib.musl.general:7434 Archived-At: On Sat, 18 Apr 2015, Rich Felker wrote: > On Wed, Apr 15, 2015 at 01:44:53AM +0300, Alexander Monakov wrote: > > This should allow spinning without constantly dirtying cache lines holding the > > spinlock value. On architectures without native atomic swap, musl implement > > a_swap by looping around a_cas. > > --- > > If I'm not mistaken this was also suggested by nsz on IRC. > > > > src/thread/pthread_spin_lock.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/src/thread/pthread_spin_lock.c b/src/thread/pthread_spin_lock.c > > index df575f0..dabcb31 100644 > > --- a/src/thread/pthread_spin_lock.c > > +++ b/src/thread/pthread_spin_lock.c > > @@ -2,6 +2,6 @@ > > > > int pthread_spin_lock(pthread_spinlock_t *s) > > { > > - while (a_swap(s, 1)) a_spin(); > > + while (a_cas(s, 0, 1)) a_spin(); > > return 0; > > } > > Would it perhaps be better to do something like this? > > while (*(volatile int *)s || a_cas(s, 0, 1)) a_spin(); I think so, Yes. Is the cast required, or is it possible to change the pthread_spinlock_t typedef to 'volatile int'? Thanks. Alexander