Re: [Xen-devel] VT is comically slow

[Daniel Veillard <veillard@xxxxxxxxxx>]

On Mon, Jul 03, 2006 at 09:58:01AM +0100, Keir Fraser wrote:
> 
> On 3 Jul 2006, at 09:48, Rik van Riel wrote:
> 
> >Looking at it a bit more closely, it appears that postgresql
> >doing disk IO from inside a fully virtualized domain totally
> >kills the CPU.
> >
> >It gets so bad that a simple "dmesg" takes 10-20 seconds to start,
> >and after that it spews data maybe 7 or 8 lines every other second.
> >Actually slower than serial console...
> >
> >This is totally unusable :(
> 
> Might you be emulating PIO? That would certainly suck. The device model 
> is supposed to support (virtual) DMA though.

  That's the first thing I though about but apparently the kernel
runs the IDE device in DMA mode if one believe the hdparm output in
that guest.

Daniel

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