Re: [RESEND] [PATCH] readahead:add blk_run_backing_dev

Wu Fengguang
2009-07-13T12:52:41Z

On Mon, Jul 13, 2009 at 08:47:31PM +0800, Ronald Moesbergen wrote:
> 2009/7/13 Wu Fengguang <fengguang.wu@intel.com>:
> > On Mon, Jul 13, 2009 at 08:12:14PM +0800, Ronald Moesbergen wrote:
> >> 2009/7/10 Vladislav Bolkhovitin <vst@vlnb.net>:
> >> >
> >> > Vladislav Bolkhovitin, on 07/10/2009 12:43 PM wrote:
> >> >>
> >> >> Ronald Moesbergen, on 07/10/2009 10:32 AM wrote:
> >> >>>>
> >> >>>> I've also long ago noticed that reading data from block devices is
> >> >>>> slower
> >> >>>> than from files from mounted on those block devices file systems. Can
> >> >>>> anybody explain it?
> >> >>>>
> >> >>>> Looks like this is strangeness #2 which we uncovered in our tests (the
> >> >>>> first
> >> >>>> one was earlier in this thread why the context RA doesn't work with
> >> >>>> cooperative I/O threads as good as it should).
> >> >>>>
> >> >>>> Can you rerun the same 11 tests over a file on the file system, please?
> >> >>>
> >> >>> I'll see what I can do. Just te be sure: you want me to run
> >> >>> blockdev-perftest on a file on the OCFS2 filesystem which is mounted
> >> >>> on the client over iScsi, right?
> >> >>
> >> >> Yes, please.
> >> >
> >> > Forgot to mention that you should also configure your backend storage as a
> >> > big file on a file system (preferably, XFS) too, not as direct device, like
> >> > /dev/vg/db-master.
> >>
> >> Ok, here are the results:
> >
> > Ronald, thanks for the numbers!
>
> You're welcome.
>
> >> client kernel: 2.6.26-15lenny3 (debian)
> >> server kernel: 2.6.29.5 with readahead patch
> >
> > Do you mean the context readahead patch?
>
> No, I meant the blk_run_backing_dev patch. The patchnames are
> confusing, I'll be sure to clarify them from now on.

That's OK. I did see previous benchmarks were not helped by context
readahead noticeably on CFQ, hehe.

Thanks,
Fengguang