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    SubjectRe: [PATCH][RF C/T/D] Unmapped page cache control - via boot parameter
    Vivek Goyal <vgoyal@redhat.com> writes:

    > Are you using CFQ in the host? What is the host kernel version? I am not sure
    > what is the problem here but you might want to play with IO controller and put
    > these guests in individual cgroups and see if you get better throughput even
    > with cache=writethrough.

    Hi. We're using the deadline IO scheduler on 2.6.32.7. We got better
    performance from deadline than from cfq when we last tested, which was
    admittedly around the 2.6.30 timescale so is now a rather outdated
    measurement.

    > If the problem is that if sync writes from different guests get intermixed
    > resulting in more seeks, IO controller might help as these writes will now
    > go on different group service trees and in CFQ, we try to service requests
    > from one service tree at a time for a period before we switch the service
    > tree.

    Thanks for the suggestion: I'll have a play with this. I currently use
    /sys/kernel/uids/N/cpu_share with one UID per guest to divide up the CPU
    between guests, but this could just as easily be done with a cgroup per
    guest if a side-effect is to provide a hint about IO independence to CFQ.

    Best wishes,

    Chris.


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