Re: [patch|rfc] add support for I/O scheduler tuning

[Vivek Goyal <vgoyal@redhat.com>]

On Wed, Nov 10, 2010 at 01:26:21PM -0500, David Zeuthen wrote:
> Hi,
> 
> On Wed, Nov 10, 2010 at 11:47 AM, Jeff Moyer <jmoyer@redhat.com> wrote:
> > Hi,
> >
> > From within the block layer in the kernel, it is difficult to
> > automatically detect the performance characteristics of the underlying
> > storage.  It was suggested by Jens Axboe at LSF2010 that we write a udev
> > rule to tune the I/O scheduler properly for most cases.  The basic
> > approach is to leave CFQ's default tunings alone for SATA disks.  For
> > everything else, turn off slice idling and bump the quantum in order to
> > drive higher queue depths.  This patch is an attempt to implement this.
> >
> > I've tested it in a variety of configurations:
> > - cciss devices
> > - sata disks
> > - sata ssds
> > - enterprise storage (single path)
> > - enterprise storage (multi-path)
> > - multiple paths to a sata disk (yes, you can actually do that!)
> >
> > The tuning works as expected in all of those scenarios.  I look forward
> > to your comments.
> 
> This looks useful, but I really think the kernel driver creating the
> block device should choose/change the defaults for the created block
> device - it seems really backwards to do this in user-space as an
> afterthought.

I think it just becomes little easier to implement in user space so that
if things don't work as expected, somebody can easily disable the rules
or somebody can easily refine the rule further to better suite their
needs instead of driver hardcoding this decision.

Thanks
Vivek