On 07/22/2013 06:21 PM, Christoffer Dall wrote:
On 22 July 2013 10:53, Raghavendra KT <raghavendra.kt.linux@xxxxxxxxx> wrote:
On Fri, Jul 19, 2013 at 7:23 PM, Marc Zyngier <marc.zyngier@xxxxxxx> wrote:
So far, when a guest executes WFE (like when waiting for a spinlock
to become unlocked), we don't do a thing and let it run uninterrupted.
Another option is to trap a blocking WFE and offer the opportunity
to the scheduler to switch to another task, potentially giving the
vcpu holding the spinlock a chance to run sooner.
Idea looks to be correct from my experiments on x86. It does bring some
percentage of benefits in overcommitted guests. Infact,
https://lkml.org/lkml/2013/7/22/41 tries to do the same thing for x86.
(this results in using ple handler heuristics in vcpu_block pach).
What about the adverse effect in the non-overcommitted case?
Ideally is should fail to schedule any other task and comeback to halt
loop. This should not hurt AFAICS. But I agree that, numbers needed to
support this argument.
For x86, I had seen no side effects with the experiments.
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