Re: Performance data of Linux native vs. Xen Dom0 and Xen DomU. Re: [Xen-devel] Direct I/O to domU seeing a 30% performance hit

["Christopher G. Stach II" <cgs@xxxxxxxxx>]

George Dunlap wrote:
> One of the strange things, though, is that the difference should be so
> big between domU and dom0, which are using the exact same same kernel
> (correct me if I'm wrong).
> 
> I'm not familiar with the I/O scheduling.  Is it possible that the I/O
> scheduling inside the domU is interacting poorly with the I/O
> scheduling in dom0?  That's one hypothesis for why domU writes are
> slower than dom0 writes; but that doesn't seem to explain why domU
> reads would be *faster* than dom0 reads.
> 
> -George

Correct me if I'm wrong, but wouldn't a file-backed block device for the
domU be reading from memory if it's cached in the dom0?  That would be a
bit faster.

Also, in the past it seemed the domU schedulers were ignored and were
implicitly noop, relying on the dom0's scheduler (which did all of the
real I/O.)  Has this changed?

-- 
Christopher G. Stach II

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