From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758193Ab3KHTRp (ORCPT ); Fri, 8 Nov 2013 14:17:45 -0500 Received: from smtprelay0217.hostedemail.com ([216.40.44.217]:36920 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1758107Ab3KHTRn (ORCPT ); Fri, 8 Nov 2013 14:17:43 -0500 X-Session-Marker: 6A6F6540706572636865732E636F6D X-Spam-Summary: 2,0,0,,d41d8cd98f00b204,joe@perches.com,:::::::::::::::,RULES_HIT:41:355:379:541:599:960:973:988:989:1260:1261:1277:1311:1313:1314:1345:1359:1373:1437:1515:1516:1518:1534:1542:1593:1594:1711:1730:1747:1777:1792:2393:2553:2559:2562:2828:3138:3139:3140:3141:3142:3355:3622:3865:3866:3867:3868:3870:3871:3872:3873:3874:4321:4384:5007:6119:7652:7903:10004:10400:10848:11026:11232:11658:11914:12296:12517:12519:12740:13019,0,RBL:none,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:fn,MSBL:0,DNSBL:none,Custom_rules:0:0:0 X-HE-Tag: iron48_25fef79da8b50 X-Filterd-Recvd-Size: 3495 Message-ID: <1383938259.2639.29.camel@joe-AO722> Subject: Re: [PATCH v2 2/2] x86: add prefetching to do_csum From: Joe Perches To: Neil Horman Cc: Dave Jones , linux-kernel@vger.kernel.org, sebastien.dugue@bull.net, Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org Date: Fri, 08 Nov 2013 11:17:39 -0800 In-Reply-To: <20131108190710.GC16052@hmsreliant.think-freely.org> References: <1381510298-20572-1-git-send-email-nhorman@tuxdriver.com> <1383751399-10298-1-git-send-email-nhorman@tuxdriver.com> <1383751399-10298-3-git-send-email-nhorman@tuxdriver.com> <20131106153429.GA26336@redhat.com> <20131106155445.GB6357@neilslaptop.think-freely.org> <1383758363.7940.19.camel@joe-AO722> <20131106200204.GB11415@hmsreliant.think-freely.org> <1383768458.7940.33.camel@joe-AO722> <20131108162502.GA16052@hmsreliant.think-freely.org> <1383929467.2639.14.camel@joe-AO722> <20131108190710.GC16052@hmsreliant.think-freely.org> Content-Type: text/plain; charset="ISO-8859-1" X-Mailer: Evolution 3.8.4-0ubuntu1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2013-11-08 at 14:07 -0500, Neil Horman wrote: > On Fri, Nov 08, 2013 at 08:51:07AM -0800, Joe Perches wrote: > > On Fri, 2013-11-08 at 11:25 -0500, Neil Horman wrote: > > > On Wed, Nov 06, 2013 at 12:07:38PM -0800, Joe Perches wrote: > > > > On Wed, 2013-11-06 at 15:02 -0500, Neil Horman wrote: > > > > > On Wed, Nov 06, 2013 at 09:19:23AM -0800, Joe Perches wrote: > > > > [] > > > > > > __always_inline instead of inline > > > > > > static __always_inline void prefetch_lines(const void *addr, size_t len) > > > > > > { > > > > > > const void *end = addr + len; > > > > > > ... > > > > > > > > > > > > buff doesn't need a void * cast in prefetch_lines > > > > > > > > > > > Actually I take back what I said here, we do need the cast, not for a conversion > > > > > from unsigned char * to void *, but rather to discard the const qualifier > > > > > without making the compiler complain. > > > > > > > > Not if the function is changed to const void * > > > > and end is also const void * as shown. > > > > > > > Addr is incremented in the for loop, so it can't be const. I could add a loop > > > counter variable on the stack, but that doesn't seem like it would help anything > > > > Perhaps you meant > > void * const addr; > > but that's not what I wrote. > > > No, I meant smoething like: > static __always_inline void prefetch_lines(const void * addr, size_t len) > { > const void *tmp = (void *)addr; > ... > for(;tmp ... > } > > > Let me know if this doesn't compile. > > It does here... > Huh, it does. But that makes very little sense to me. by qualifying addr as > const, how is the compiler not throwing a warning in the for loop about us > incrementing that same variable? Because it points to const data but is not const itself. void * const foo; /* value of foo can't change */ const void *bar; /* data pointed to by bar can't change */ const void * const baz; /* Neither baz nor data pointed to by baz can change */