From: ebiederm@xmission.com (Eric W. Biederman) To: Cliff Wickman <cpw@sgi.com> Cc: kexec@lists.infradead.org, mingo@elte.hu, linux-kernel@vger.kernel.org Subject: Re: [PATCH] x86: copy_oldmem_page using cached addressing Date: Wed, 08 Sep 2010 12:19:43 -0700 [thread overview] Message-ID: <m1eid4gi0g.fsf@fess.ebiederm.org> (raw) In-Reply-To: <E1OtMLz-0001yp-Ia@eag09.americas.sgi.com> (Cliff Wickman's message of "Wed, 08 Sep 2010 10:14:27 -0500") Cliff Wickman <cpw@sgi.com> writes: > From: Cliff Wickman <cpw@sgi.com> > > 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" <ebiederm@xmission.com> > > Signed-off-by: Cliff Wickman <cpw@sgi.com> > --- > 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
WARNING: multiple messages have this Message-ID (diff)
From: ebiederm@xmission.com (Eric W. Biederman) To: Cliff Wickman <cpw@sgi.com> Cc: mingo@elte.hu, kexec@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] x86: copy_oldmem_page using cached addressing Date: Wed, 08 Sep 2010 12:19:43 -0700 [thread overview] Message-ID: <m1eid4gi0g.fsf@fess.ebiederm.org> (raw) In-Reply-To: <E1OtMLz-0001yp-Ia@eag09.americas.sgi.com> (Cliff Wickman's message of "Wed, 08 Sep 2010 10:14:27 -0500") Cliff Wickman <cpw@sgi.com> writes: > From: Cliff Wickman <cpw@sgi.com> > > 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" <ebiederm@xmission.com> > > Signed-off-by: Cliff Wickman <cpw@sgi.com> > --- > 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
next prev parent reply other threads:[~2010-09-08 19:19 UTC|newest] Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top 2010-09-08 15:14 [PATCH] x86: copy_oldmem_page using cached addressing Cliff Wickman 2010-09-08 15:14 ` Cliff Wickman 2010-09-08 19:19 ` Eric W. Biederman [this message] 2010-09-08 19:19 ` Eric W. Biederman 2010-09-09 7:48 ` Ingo Molnar 2010-09-09 7:48 ` Ingo Molnar 2010-09-08 19:42 ` Andi Kleen 2010-09-08 19:42 ` Andi Kleen 2010-09-09 11:57 ` [tip:x86/mm] x86, kdump: Change copy_oldmem_page() to use " tip-bot for Cliff Wickman
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