RE: [Xen-devel] planned csched improvements?

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

>From: Jan Beulich
>Sent: 2009年10月9日 22:54
>
>After the original announcement of plans to do some work on 
>csched there
>wasn't much activity, so I'd like to ask about some 
>observations that I made
>with the current implementation and whether it would be expected that
>those planned changes would take care of them.
>
>On a lightly loaded many-core non-hyperthreaded system (e.g. a single
>CPU bound process in one VM, and only some background load elsewhere),
>I see this CPU bound vCPU permanently switch between sockets, which is
>a result of csched_cpu_pick() eagerly moving vCPU-s to "more idle"
>sockets. It would seem that some minimal latency consideration might be
>useful to get added here, so that a very brief interruption by another
>vCPU doesn't result in unnecessary migration.

there's a migration delay (default is 1ms) to judge cache hotness and
thus avoid unnecessary migration. However so far it's only checked 
when one cpu wants to steal vcpus from other runqueue. Possibly it
makes sense to add this check to csched_vcpu_acct, as a cold cache
and cascade of other VCPU migrations could easily beat benefit on a 
"more idle" socket.

Thanks,
Kevin

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