Re: [Xen-devel] [PATCH] Quick path for PIO instructions which cut more than half of the expense

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 22/12/2008 10:16, "Xiang, Kai" <kai.xiang@xxxxxxxxx> wrote:

> 3) The influence for more realistic workloads:
> We tested on Windows 2003 Server Guest, while using IOmeter to run a Disk
> bound test, the IO pattern is "Default" which use 67% random read and 33%
> random write with 2K request size.
> To reduce the influence of file cache, I run 3 times (1 minutes each) from the
> start of the computer (both xen and the guest)
> 
> Compare before and after
>          IO per second (3 runs)    |  average response time (3 runs)
> ----------------------------------------------------------------
> Before: 100.004; 109.447; 110.801  |  9.988;  9.133;  9.022
> After:  101.951; 110.893; 114.179  |  9.806;  9.016;  8.756
> ------------------------------------------------------------------
> 
> So we are having a 1%~3% percent IO performance gain while reduce the average
> response time by 2%~3% at the same time.
> Considering this is just an ordinary SATA disk and an IO bound workload, we
> are expecting more with faster Disks and more cached IO.

The difference is in the noise, almost. Not, I think, sufficient for me ever
to want to see the VMX PIO code back in Xen ever again. Those who actually
care about performance would run PV drivers anyway, and see much greater
speedups.

 -- Keir



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