linux-kernel - Re: [rfc] lockless get_user

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Message-Id: <1200513482.6935.15.camel@norville.austin.ibm.com>
Date:	Wed, 16 Jan 2008 13:58:02 -0600
From:	Dave Kleikamp <shaggy@...ux.vnet.ibm.com>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	Ken Chen <kenchen@...gle.com>,
	Badari Pulavarty <pbadari@...il.com>,
	linux-mm <linux-mm@...ck.org>, tony.luck@...el.com,
	Adam Litke <agl@...ibm.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [rfc] lockless get_user_pages for dio (and more)

On Wed, 2007-12-12 at 16:40 +1100, Nick Piggin wrote:
> On Wednesday 12 December 2007 16:11, Dave Kleikamp wrote:
> > On Wed, 2007-12-12 at 15:57 +1100, Nick Piggin wrote:

> > > Anyway, I am hoping that someone will one day and test if this and
> > > find it helps their workload, but on the other hand, if it doesn't
> > > help anyone then we don't have to worry about adding it to the
> > > kernel ;) I don't have any real setups that hammers DIO with threads.
> > > I'm guessing DB2 and/or Oracle does?
> >
> > I'll try to get someone to run a DB2 benchmark and see what it looks
> > like.
> 
> That would be great if you could.

We weren't able to get in any runs before the holidays, but we finally
have some good news from our performance team:

"To test the effects of the patch, an OLTP workload was run on an IBM
x3850 M2 server with 2 processors (quad-core Intel Xeon processors at
2.93 GHz) using IBM DB2 v9.5 running Linux 2.6.24rc7 kernel. Comparing
runs with and without the patch resulted in an overall performance
benefit of ~9.8%. Correspondingly, oprofiles showed that samples from
__up_read and __down_read routines that is seen during thread contention
for system resources was reduced from 2.8% down to .05%. Monitoring
the /proc/vmstat output from the patched run showed that the counter for
fast_gup contained a very high number while the fast_gup_slow value was
zero."

Great work, Nick!

Thanks,
Shaggy
-- 
David Kleikamp
IBM Linux Technology Center

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