[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Re: poor domU VBD performance.
> On Tuesday 29 March 2005 02:13, Ian Pratt wrote: > > > It looks like there might be a problem were we are not > > > getting a timely > > > response back from dom0 VBD driver that the io request is > > > complete, which > > > limits the number of outstanding requests to a level which > > > cannot keep the > > > disk utilized well. If you drive enough IO outstanding > > > requests (which can > > > be done with either o-direct with large request or a much > > > larger readahead > > > setting with buffered IO), it's not an issue. > > > > Andrew, please could you try this with a 2.4 dom0, 2.6 domU. > > 2.4 might be a little while for me, as I an running Fedora core3 with udev. > If anyone has any easy way to get around the hotplug/udev stuff, then I can > do this. You can run a populated /dev "underneath" the udev stuff quite happily; e.g. if you boot into FC3 w/ udev do: cd /dev/ tar zcpf /root/foo.tgz . If you can boot from a rescue CD or sim, just mount your FC3 partition and untar the device nodes. Works just fine. > I did run a sequential read on a single disk again (using noop IO schedulers > in both domains) with various request sizes with o_direct while capturing > iostsat output. The results are interesting. I have included the data in a > file because it would just line wrap an be unreadable in this email text. > Notice the service commit times for domU tests. It's like the IO request > queue is being plugged for a minimum of 10ms in dom0. Merges happening for > >4K requests in dom0 (while hosting domU's IO) seem to support this. [snip] Ah - thanks for this -- will take a detailed look shortly. cheers, S. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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