Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750919AbXAXKAG (ORCPT ); Wed, 24 Jan 2007 05:00:06 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750925AbXAXKAG (ORCPT ); Wed, 24 Jan 2007 05:00:06 -0500 Received: from ozlabs.org ([203.10.76.45]:47978 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750919AbXAXKAE (ORCPT ); Wed, 24 Jan 2007 05:00:04 -0500 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <17847.8700.118329.777644@cargo.ozlabs.ibm.com> Date: Wed, 24 Jan 2007 20:08:12 +1100 From: Paul Mackerras To: Mathieu Desnoyers Cc: linux-kernel@vger.kernel.org, Andrew Morton , Ingo Molnar , Greg Kroah-Hartman , Christoph Hellwig , "Martin J. Bligh" , linuxppc-dev@ozlabs.org, Douglas Niehaus , ltt-dev@shafik.org, systemtap@sources.redhat.com, Thomas Gleixner Subject: Re: [PATCH 7/10] local_t : powerpc In-Reply-To: <20061221002705.GW28643@Krystal> References: <20061221001545.GP28643@Krystal> <20061221002705.GW28643@Krystal> X-Mailer: VM 7.19 under Emacs 21.4.1 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1241 Lines: 37 Mathieu Desnoyers writes: > +static __inline__ int local_dec_if_positive(local_t *l) > +{ > + int t; > + > + __asm__ __volatile__( > +"1: lwarx %0,0,%1 # local_dec_if_positive\n\ > + addic. %0,%0,-1\n\ > + blt- 2f\n" > + PPC405_ERR77(0,%1) > +" stwcx. %0,0,%1\n\ > + bne- 1b" This has the same bugs that we fixed recently in atomic_dec_if_positive; first, on 64-bit machines, the lwarx will zero-extend the word loaded from memory, and so the result of the addic will be negative only if the word was originally 0. Secondly, even on 32-bit machines, 0x80000000 will be considered positive since decrementing it gives 0x7fffffff, which is positive. > +/* Use these for per-cpu local_t variables: on some archs they are > + * much more efficient than these naive implementations. Note they take > + * a variable, not an address. > + * > + * This could be done better if we moved the per cpu data directly > + * after GS. > + */ What's "GS"? Does this comment really apply on powerpc? Paul. - 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/