From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from out01.mta.xmission.com ([166.70.13.231]) by bombadil.infradead.org with esmtp (Exim 4.72 #1 (Red Hat Linux)) id 1OtQBj-00007g-7O for kexec@lists.infradead.org; Wed, 08 Sep 2010 19:20:08 +0000 From: ebiederm@xmission.com (Eric W. Biederman) References: Date: Wed, 08 Sep 2010 12:19:43 -0700 In-Reply-To: (Cliff Wickman's message of "Wed, 08 Sep 2010 10:14:27 -0500") Message-ID: MIME-Version: 1.0 Subject: Re: [PATCH] x86: copy_oldmem_page using cached addressing List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: kexec-bounces@lists.infradead.org Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: Cliff Wickman Cc: mingo@elte.hu, kexec@lists.infradead.org, linux-kernel@vger.kernel.org Cliff Wickman writes: > From: Cliff Wickman > > The copy of /proc/vmcore to a user buffer proceeds much faster > if the kernel addresses memory as cached. > > With this patch we have seen an increase in transfer rate from less than > 15MB/s to 80-460MB/s, depending on size of the transfer. This makes > a big difference in time needed to save a system dump. > > (Does anyone know of a reason why copy_oldmem_page() would need > to use uncached addresses?) > > Diffed against 2.6.36-rc3 I believe this code simply predates being able to specify the caching attributes at ioremap time. Being cached in this case actually looks more correct, as that is the default for RAM and we are talking about RAM. Ultimately either there is another cpu running wild with these pages mapped with some random set of attributes, and we cannot get the permissions right or we have captured all of the cpus and this is the only mapping so it doesn't matter. Acked-by: "Eric W. Biederman" > > Signed-off-by: Cliff Wickman > --- > arch/x86/kernel/crash_dump_64.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > Index: linus.current/arch/x86/kernel/crash_dump_64.c > =================================================================== > --- linus.current.orig/arch/x86/kernel/crash_dump_64.c > +++ linus.current/arch/x86/kernel/crash_dump_64.c > @@ -34,7 +34,7 @@ ssize_t copy_oldmem_page(unsigned long p > if (!csize) > return 0; > > - vaddr = ioremap(pfn << PAGE_SHIFT, PAGE_SIZE); > + vaddr = ioremap_cache(pfn << PAGE_SHIFT, PAGE_SIZE); > if (!vaddr) > return -ENOMEM; > > > _______________________________________________ > kexec mailing list > kexec@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/kexec _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec