Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754208Ab2HPOMc (ORCPT ); Thu, 16 Aug 2012 10:12:32 -0400 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:51484 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753667Ab2HPOM3 (ORCPT ); Thu, 16 Aug 2012 10:12:29 -0400 Date: Thu, 16 Aug 2012 15:11:53 +0100 From: Catalin Marinas To: Arnd Bergmann Cc: Will Deacon , "linux-arch@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Marc Zyngier Subject: Re: [PATCH v2 26/31] arm64: Miscellaneous library functions Message-ID: <20120816141153.GC30876@arm.com> References: <1344966752-16102-1-git-send-email-catalin.marinas@arm.com> <201208151521.14663.arnd@arndb.de> <20120816105709.GK31784@mudshark.cambridge.arm.com> <201208161300.32830.arnd@arndb.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201208161300.32830.arnd@arndb.de> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1787 Lines: 46 On Thu, Aug 16, 2012 at 02:00:32PM +0100, Arnd Bergmann wrote: > On Thursday 16 August 2012, Will Deacon wrote: > > > > + > > > > +#include > > > > +#include > > > > +#include > > > > + > > > > +#ifdef CONFIG_SMP > > > > +arch_spinlock_t __atomic_hash[ATOMIC_HASH_SIZE] __lock_aligned = { > > > > + [0 ... (ATOMIC_HASH_SIZE-1)] = __ARCH_SPIN_LOCK_UNLOCKED > > > > +}; > > > > +#endif > > > > > > What? > > > > > > I suppose this is a leftover from an earlier version using the > > > generic bitops, right? > > > > We currently use the generic atomic bitops (asm-generic/bitops/atomic.h) > > which contains: > > > > # define ATOMIC_HASH(a) (&(__atomic_hash[ (((unsigned long) a)/L1_CACHE_BYTES) & (ATOMIC_HASH_SIZE-1) ])) > > > > so we have to provide a definition for the array. We have additional patches > > containing optimised assembly implementations of the atomic bitops which we > > will push later, once we've got some hardware to benchmark with. > > > > Ah, I was confusing this with the asm/atomic.h stuff, for which you already > provide an optimized version. > > The generic atomic bitops are really horrible in performance and I would > expect that there is just one obvious way to implement bitops using ldaxr/stlxr, > so I recommend just doing that even if you have no hardware for benchmarking. As Will said, we have the code already but I dropped it from the initial set patches to be reviewed to keep them simpler. They will be added later. -- Catalin -- 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/