Re: [RFC PATCH] cfq-iosced: Implement IOPS mode and group_idle tunable V3

[Vivek Goyal <vgoyal@redhat.com>]

On Sat, Jul 24, 2010 at 11:07:07AM +0200, Corrado Zoccolo wrote:
> On Sat, Jul 24, 2010 at 10:51 AM, Christoph Hellwig <hch@infradead.org> wrote:
> > To me this sounds like slice_idle=0 is the right default then, as it
> > gives useful behaviour for all systems linux runs on.
> No, it will give bad performance on single disks, possibly worse than
> deadline (deadline at least sorts the requests between different
> queues, while CFQ with slice_idle=0 doesn't even do this for readers).

> Setting slice_idle to 0 should be considered only when a single
> sequential reader cannot saturate the disk bandwidth, and this happens
> only on smart enough hardware with large number of spindles.

I was thinking of writting a user space utility which can launch
increasing number of parallel direct/buffered reads from device and if
device can sustain more than 1 parallel reads with increasing throughput,
then it probably is good indicator that one might be better off with
slice_idle=0.

Will try that today...

Vivek