Messages in this thread | | | Date | Fri, 21 Sep 2012 23:15:40 +0530 | From | Raghavendra K T <> | Subject | Re: [PATCH RFC 2/2] kvm: Be courteous to other VMs in overcommitted scenario in PLE handler |
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On 09/21/2012 07:22 PM, Rik van Riel wrote: > On 09/21/2012 09:46 AM, Takuya Yoshikawa wrote: >> On Fri, 21 Sep 2012 17:30:20 +0530 >> Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com> wrote: >> >>> From: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com> >>> >>> When PLE handler fails to find a better candidate to yield_to, it >>> goes back and does spin again. This is acceptable when we do not >>> have overcommit. >>> But in overcommitted scenarios (especially when we have large >>> number of small guests), it is better to yield. >>> >>> Reviewed-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com> >>> Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com> >>> --- >>> virt/kvm/kvm_main.c | 4 ++++ >>> 1 files changed, 4 insertions(+), 0 deletions(-) >>> >>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c >>> index 8323685..713b677 100644 >>> --- a/virt/kvm/kvm_main.c >>> +++ b/virt/kvm/kvm_main.c >>> @@ -1660,6 +1660,10 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me) >>> } >>> } >>> } >>> + /* In overcommitted cases, yield instead of spinning */ >>> + if (!yielded && rq_nr_running() > 1) >>> + schedule(); >> >> How about doing cond_resched() instead? > > Actually, an actual call to yield() may be better. > > That will set scheduler hints to make the scheduler pick > another task for one round, while preserving this task's > top position in the runqueue.
I am not a scheduler expert, but I am also inclined towards Rik's suggestion here since we set skip buddy here. Takuya?
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