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

["Liang Yang" <multisyncfe991@xxxxxxxxxxx>]

Hi,

I did not use any file backed block devices. To get the real disk I/O 
performance for guest domains, all the guest domain OS are installed on the 
separate logic volumes (each guest domain is installed on independent hard 
drives).
I tried to change the I/O scheduler for both guest domain (noop is the 
default) and domain0 to anticipatory, but the results are the same as I 
collected before.
Regards,

Liang

----- Original Message ----- 
From: "Christopher G. Stach II" <cgs@xxxxxxxxx>
To: "George Dunlap" <gdunlap@xxxxxxxxxxxxx>
Cc: "Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>; "Emmanuel Ackaouy" 
<ack@xxxxxxxxxxxxx>; "Liang Yang" <multisyncfe991@xxxxxxxxxxx>; "xen-devel" 
<xen-devel@xxxxxxxxxxxxxxxxxxx>; "John Byrne" <john.l.byrne@xxxxxx>
Sent: Monday, November 13, 2006 8:49 AM
Subject: 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

> 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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