Re: cfq-iosched: tiobench regression

Shaohua Li
2009-12-24T09:19:23Z

On Thu, Dec 24, 2009 at 03:48:38PM +0800, Gui Jianfeng wrote:
> Shaohua Li wrote:
> > We see about 30% regression in tiobench 32 threads 80M file sequential read.
> > The regression is caused by below commits.
> >
> > 5db5d64277bf390056b1a87d0bb288c8b8553f96
> > The commit makes the slice too small. In the test, the slice is limitted
> > to 2 * idle_slice(300ms/32 < 2*idle_slice). This dramatically impacts io
> > thoughput. The low_latency knob used to be only impact random io, now it
> > impacts sequential io too. Any idea to fix it?
>
> Hi Shaohua,
>
> IMHO this shouldn't be a problem. Currently, low_latency is used to improve
> the latency for the whole system. If someone would like to achieve high throughput,
> just turn off low_latency knob.
The concern is low_latency is default on. A end user is unlikely to know the knob.

Thanks,
Shaohua