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Subject: Re: NFS client latencies
From: Trond Myklebust <trond.myklebust@fys.uio.no>
To: Lee Revell <rlrevell@joe-job.com>
Cc: Andrew Morton <akpm@osdl.org>, mingo@elte.hu, linux-kernel@vger.kernel.org
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on den 30.03.2005 Klokka 21:47 (-0500) skreiv Lee Revell:
> On Wed, 2005-03-30 at 18:39 -0800, Andrew Morton wrote:
> > Lee Revell <rlrevell@joe-job.com> wrote:
> > >
> > > > Yes. Together with the radix tree-based sorting of dirty requests,
> > >  > that's pretty much what I've spent most of today doing. Lee, could you
> > >  > see how the attached combined patch changes your latency numbers?
> > >  > 
> > > 
> > >  Different code path, and the latency is worse.  See the attached ~7ms
> > >  trace.
> > 
> > Is a bunch of gobbledygook.  Hows about you interpret it for us?
> > 
> 
> Sorry.  When I summarized them before, Ingo just asked for the full
> verbose trace.
> 
> The 7 ms are spent in this loop:
> 
>  radix_tree_tag_clear+0xe/0xd0 <c01e040e> (nfs_scan_lock_dirty+0xb2/0xf0 <c01c3a22>)
>  nfs_set_page_writeback_locked+0xe/0x60 <c01c357e> (nfs_scan_lock_dirty+0x8d/0xf0 <c01c39fd>)
>  radix_tree_tag_set+0xe/0xa0 <c01e036e> (nfs_set_page_writeback_locked+0x4b/0x60 <c01c35bb>)
>  radix_tree_tag_clear+0xe/0xd0 <c01e040e> (nfs_scan_lock_dirty+0xb2/0xf0 <c01c3a22>)


Which is basically confirming what the guys from Bull already told me,
namely that the radix tree tag stuff is much less efficient that what
we've got now. I never saw their patches, though, so I was curious to
try it for myself.

Cheers,
  Trond

-- 
Trond Myklebust <trond.myklebust@fys.uio.no>

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