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From: Ingo Molnar <mingo@elte.hu>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: kexec@lists.infradead.org, Cliff Wickman <cpw@sgi.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86: copy_oldmem_page using cached addressing
Date: Thu, 9 Sep 2010 09:48:13 +0200	[thread overview]
Message-ID: <20100909074813.GA8355@elte.hu> (raw)
In-Reply-To: <m1eid4gi0g.fsf@fess.ebiederm.org>


* Eric W. Biederman <ebiederm@xmission.com> wrote:

> 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>

Applied, thanks guys. Note, i also added a -stable tag, as kdump is 
typically used with enterprise setups and we want this (low-risk, 
high-impact) improvement to be propagated far back the -stable series.

Thanks,

	Ingo

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WARNING: multiple messages have this Message-ID (diff)
From: Ingo Molnar <mingo@elte.hu>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Cliff Wickman <cpw@sgi.com>,
	kexec@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86: copy_oldmem_page using cached addressing
Date: Thu, 9 Sep 2010 09:48:13 +0200	[thread overview]
Message-ID: <20100909074813.GA8355@elte.hu> (raw)
In-Reply-To: <m1eid4gi0g.fsf@fess.ebiederm.org>


* Eric W. Biederman <ebiederm@xmission.com> wrote:

> 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>

Applied, thanks guys. Note, i also added a -stable tag, as kdump is 
typically used with enterprise setups and we want this (low-risk, 
high-impact) improvement to be propagated far back the -stable series.

Thanks,

	Ingo

  reply	other threads:[~2010-09-09  7:48 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
2010-09-08 19:19   ` Eric W. Biederman
2010-09-09  7:48   ` Ingo Molnar [this message]
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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