From: Andi Kleen <andi@firstfloor.org>
To: "J. Bruce Fields" <bfields@fieldses.org>
Cc: Andi Kleen <andi@firstfloor.org>, Neil Brown <neilb@suse.de>,
Alan Cox <alan@lxorguk.ukuu.org.uk>,
"Patrick J. LoPresti" <lopresti@gmail.com>,
linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org,
linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: Proposal: Use hi-res clock for file timestamps
Date: Wed, 18 Aug 2010 21:25:08 +0200 [thread overview]
Message-ID: <20100818192508.GC6567@basil.fritz.box> (raw)
In-Reply-To: <20100818185456.GD13050@fieldses.org>
On Wed, Aug 18, 2010 at 02:54:56PM -0400, J. Bruce Fields wrote:
> On Wed, Aug 18, 2010 at 07:50:40PM +0200, Andi Kleen wrote:
> > > - nfsd updates it whenever it reads an mtime out of an inode that matches
> > > current_fs_time to the granularity of 1/HZ.
> >
> > That means you have a very very hot cache line on a larger system
> > if there are a lot of mtime changes. Probably a bad idea.
>
> Only if those mtime changes are also followed immediately by nfsd reads
> of the mtime.
If multiple writers are changing the same location in quick succession
you have a hot cache line that gets bounced around. It doesn't need reads,
although reads make it even worse.
There's a lot of effort currently to make the VFS more parallel
and less synchronized and it would be bad again to regress here again.
-Andi
--
ak@linux.intel.com -- Speaking for myself only.
next prev parent reply other threads:[~2010-08-18 19:25 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-08-13 18:25 Proposal: Use hi-res clock for file timestamps Patrick J. LoPresti
2010-08-13 18:45 ` john stultz
2010-08-13 18:57 ` Patrick J. LoPresti
2010-08-13 19:09 ` john stultz
2010-08-13 20:53 ` Patrick J. LoPresti
2010-08-14 16:45 ` Patrick J. LoPresti
2010-08-15 1:50 ` Bret Towe
2010-08-13 19:57 ` Jim Rees
2010-08-13 20:26 ` john stultz
2010-08-13 20:52 ` Jim Rees
2010-08-17 14:54 ` Andi Kleen
2010-08-17 17:41 ` J. Bruce Fields
2010-08-17 18:29 ` Andi Kleen
2010-08-17 18:50 ` Patrick J. LoPresti
2010-08-17 19:04 ` J. Bruce Fields
2010-08-17 19:18 ` Patrick J. LoPresti
2010-08-17 19:39 ` Alan Cox
2010-08-17 19:29 ` J. Bruce Fields
2010-08-17 19:52 ` Alan Cox
2010-08-18 5:53 ` Neil Brown
2010-08-18 14:46 ` Patrick J. LoPresti
2010-08-18 17:32 ` J. Bruce Fields
2010-08-18 18:15 ` Chuck Lever
2010-08-18 23:41 ` Neil Brown
2010-08-19 0:52 ` Neil Brown
2010-08-19 2:08 ` J. Bruce Fields
2010-08-19 2:44 ` Neil Brown
2010-08-19 22:46 ` J. Bruce Fields
2010-08-18 23:47 ` Neil Brown
2010-08-18 17:50 ` Andi Kleen
2010-08-18 18:54 ` J. Bruce Fields
2010-08-18 19:25 ` Andi Kleen [this message]
2010-08-18 19:30 ` J. Bruce Fields
2010-08-17 19:34 ` Patrick J. LoPresti
2010-08-17 19:54 ` Alan Cox
2010-08-17 19:43 ` Patrick J. LoPresti
2010-08-17 19:45 ` J. Bruce Fields
2010-08-18 18:12 ` J. Bruce Fields
2010-08-19 1:41 ` john stultz
2010-08-19 2:31 ` J. Bruce Fields
2010-08-19 3:17 ` john stultz
2010-08-19 22:53 ` J. Bruce Fields
2010-08-18 18:20 ` David Woodhouse
2010-08-18 18:32 ` Patrick J. LoPresti
2010-08-18 18:53 ` Andi Kleen
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