From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758236Ab3KHUIS (ORCPT ); Fri, 8 Nov 2013 15:08:18 -0500 Received: from charlotte.tuxdriver.com ([70.61.120.58]:46895 "EHLO smtp.tuxdriver.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757583Ab3KHUIR (ORCPT ); Fri, 8 Nov 2013 15:08:17 -0500 Date: Fri, 8 Nov 2013 15:08:03 -0500 From: Neil Horman To: Joe Perches Cc: Dave Jones , linux-kernel@vger.kernel.org, sebastien.dugue@bull.net, Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org Subject: Re: [PATCH v2 2/2] x86: add prefetching to do_csum Message-ID: <20131108200803.GD16052@hmsreliant.think-freely.org> References: <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> <1383938259.2639.29.camel@joe-AO722> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1383938259.2639.29.camel@joe-AO722> User-Agent: Mutt/1.5.21 (2010-09-15) X-Spam-Score: -2.9 (--) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 08, 2013 at 11:17:39AM -0800, Joe Perches wrote: > 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 */ > Doh! Wow, that was just staring me in the face and I missed it :) Thanks for pointing it out. I'll make that adjustment Neil