Messages in this thread Patch in this message | | | Date | Tue, 19 Jun 2012 16:51:04 -0400 | From | Rik van Riel <> | Subject | [PATCH] kvm: handle last_boosted_vcpu = 0 case |
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On Wed, 20 Jun 2012 01:50:50 +0530 Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com> wrote:
> > In ple handler code, last_boosted_vcpu (lbv) variable is > serving as reference point to start when we enter.
> Also statistical analysis (below) is showing lbv is not very well > distributed with current approach.
You are the second person to spot this bug today (yes, today).
Due to time zones, the first person has not had a chance yet to test the patch below, which might fix the issue...
Please let me know how it goes.
====8<====
If last_boosted_vcpu == 0, then we fall through all test cases and may end up with all VCPUs pouncing on vcpu 0. With a large enough guest, this can result in enormous runqueue lock contention, which can prevent vcpu0 from running, leading to a livelock.
Changing < to <= makes sure we properly handle that case.
Signed-off-by: Rik van Riel <riel@redhat.com> --- virt/kvm/kvm_main.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 7e14068..1da542b 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1586,7 +1586,7 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me) */ for (pass = 0; pass < 2 && !yielded; pass++) { kvm_for_each_vcpu(i, vcpu, kvm) { - if (!pass && i < last_boosted_vcpu) { + if (!pass && i <= last_boosted_vcpu) { i = last_boosted_vcpu; continue; } else if (pass && i > last_boosted_vcpu)
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