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

[Jens Axboe]

On Tue, Feb 27 2007, Avi Kivity wrote:
> Ingo Molnar wrote:
> >* Avi Kivity <avi@xxxxxxxxxx> 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

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