From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/7432 Path: news.gmane.org!not-for-mail From: Rich Felker Newsgroups: gmane.linux.lib.musl.general Subject: Re: [PATCH] Use CAS instead of atomic swap to implement spinlock Date: Sat, 18 Apr 2015 20:24:33 -0400 Message-ID: <20150419002433.GL6817@brightrain.aerifal.cx> References: <1429051493-2821-1-git-send-email-amonakov@ispras.ru> 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 1429403088 7837 80.91.229.3 (19 Apr 2015 00:24:48 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sun, 19 Apr 2015 00:24:48 +0000 (UTC) To: musl@lists.openwall.com Original-X-From: musl-return-7445-gllmg-musl=m.gmane.org@lists.openwall.com Sun Apr 19 02:24:48 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 1Yjd2V-0007R7-Kj for gllmg-musl@m.gmane.org; Sun, 19 Apr 2015 02:24:47 +0200 Original-Received: (qmail 12017 invoked by uid 550); 19 Apr 2015 00:24:45 -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 11999 invoked from network); 19 Apr 2015 00:24:45 -0000 Content-Disposition: inline In-Reply-To: <1429051493-2821-1-git-send-email-amonakov@ispras.ru> User-Agent: Mutt/1.5.21 (2010-09-15) Original-Sender: Rich Felker Xref: news.gmane.org gmane.linux.lib.musl.general:7432 Archived-At: 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(); Rich