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Re: [Xen-devel] I/O bound dom0 locks-ups

On Fri, 2005-02-04 at 16:15 -0500, John L Griffin wrote:
> > 1) Is it most likely that this is caused by how the schedulers work or
> > is it due to using loop files?
> In my experience, it's due to using loop files.  High I/O loads in the 
> guests killed dom0's interactivity and I/O response time.  Since you have 
> LVM set up already for the swap files, it should be easy to verify this 
> with an all-LVM configuration?

I thought of this just as I clicked on send, yes it was easy for me to
setup a test domain with a LVM backing.   With this dom0 churns along
happily using some CPU for xenblkd (normally 1-2%, bursts up to 6%).  0
% of CPU is in the "IO wait" state.  Note before I was running just
"stress --hdd 1", these numbers represent running "stress --cpu 8 --io 4
--vm 2 --vm-bytes 128M --hdd 4".
I knew the loop interface added some overhead, just didn't realize it
was that much.  I had only counted on it adding a few % to CPU for the
loop kernel thread.  Do any developers thing opening the loop files
O_DIRECT is possible and if so, would it help performance?  I think the
major problem is that read() and write() calls with O_DIRECT must be
aligned to the page size of the architecture.

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