Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751689AbaBGRIu (ORCPT ); Fri, 7 Feb 2014 12:08:50 -0500 Received: from verein.lst.de ([213.95.11.211]:44622 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750775AbaBGRIt (ORCPT ); Fri, 7 Feb 2014 12:08:49 -0500 Date: Fri, 7 Feb 2014 18:08:45 +0100 From: Torsten Duwe To: Peter Zijlstra Cc: Scott Wood , linux-kernel@vger.kernel.org, Paul Mackerras , Anton Blanchard , Tom Musta , "Paul E. McKenney" , linuxppc-dev@lists.ozlabs.org, Ingo Molnar Subject: Re: [PATCH] Convert powerpc simple spinlocks into ticket locks Message-ID: <20140207170845.GD2107@lst.de> References: <20140206103736.GA18054@lst.de> <20140206163837.GT2936@laptop.programming.kicks-ass.net> <20140206173727.GA13048@lst.de> <1391717992.6733.232.camel@snotra.buserror.net> <20140207090248.GB26811@lst.de> <20140207103139.GP5002@laptop.programming.kicks-ass.net> <20140207104530.GG5126@laptop.programming.kicks-ass.net> <20140207114949.GA2107@lst.de> <20140207122837.GA3104@twins.programming.kicks-ass.net> <20140207151847.GB3104@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140207151847.GB3104@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 07, 2014 at 04:18:47PM +0100, Peter Zijlstra wrote: > On Fri, Feb 07, 2014 at 01:28:37PM +0100, Peter Zijlstra wrote: > > Anyway, you can do a version with lwarx/stwcx if you're looking get rid > > of lharx. > > the below seems to compile into relatively ok asm. It can be done better > if you write the entire thing by hand though. [...] > > static inline unsigned int xadd(unsigned int *v, unsigned int i) > { > int t, ret; > > __asm__ __volatile__ ( > "1: lwarx %0, 0, %4\n" > " mr %1, %0\n" > " add %0, %3, %0\n" > " stwcx. %0, %0, %4\n" > " bne- 1b\n" > : "=&r" (t), "=&r" (ret), "+m" (*v) > : "r" (i), "r" (v) > : "cc"); > > return ret; > } > I don't like this xadd thing -- it's so x86 ;) x86 has its LOCK prefix, ppc has ll/sc. That should be reflected somehow IMHO. Maybe if xadd became mandatory for some kernel library. > > void ticket_unlock(tickets_t *lock) > { > ticket_t tail = lock->tail + 1; > > /* > * The store is save against the xadd for it will make the ll/sc fail > * and try again. Aside from that PowerISA guarantees single-copy > * atomicy for half-word writes. > * > * And since only the lock owner will ever write the tail, we're good. > */ > smp_store_release(&lock->tail, tail); > } Yeah, let's try that on top of v2 (just posted). First, I want to see v2 work as nicely as v1 -- compiling a debug kernel takes a while... Torsten -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/