Re: A quick fio test (was Re: [patch 00/13] Syslets, "Threadlets", generic AIO support, v3)

Jens Axboe
2007-02-27T18:49:28Z

On Tue, Feb 27 2007, Avi Kivity wrote:
> Ingo Molnar wrote:
> >* Avi Kivity <avi@argo.co.il> wrote:
> >
> >
> >>But what about cpu usage? At these low levels, the cpu is probably
> >>underutilized. It would be interesting to measure cpu time per I/O
> >>request (or, alternatively, use an I/O subsystem that can saturate the
> >>processors).
> >>
> >
> >yeah - that's what testing on ramdisk (Jens') or on a loopback block
> >device (mine) approximates to a certain degree.
> >
> >
>
> Ramdisks or fully cached loopback return immediately, so cache thrashing
> effects don't show up.
>
> Maybe a device mapper delay target or nbd + O_DIRECT can insert delays
> to make the workload more disk-like.

Take a look at scsi-debug, it can do at least some of that.

--
Jens Axboe