Messages in this thread | | | Date | Wed, 17 Mar 2010 19:11:32 +0000 | From | Chris Webb <> | Subject | Re: [PATCH][RF C/T/D] Unmapped page cache control - via boot parameter |
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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from deadline than from cfq when we last tested, which was admittedly around the 2.6.30 timescale so is now a rather outdated measurement.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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