Messages in this thread | | | Subject | Re: [PART1 RFC v3 12/12] svm: Manage vcpu load/unload when enable AVIC | From | Suravee Suthikulpanit <> | Date | Tue, 5 Apr 2016 17:07:39 +0700 |
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Hi Radim,
On 3/31/16 21:19, Radim Krčmář wrote: > 2016-03-31 15:52+0700, Suravee Suthikulpanit: >> On 03/19/2016 04:44 AM, Radim Krčmář wrote: >>> 2016-03-18 01:09-0500, Suravee Suthikulpanit: >>>> + } else { >>>> + new_entry = READ_ONCE(*entry); >>>> + /** >>>> + * This handles the case when vcpu is scheduled out >>>> + * and has not yet not called blocking. We save the >>>> + * AVIC running flag so that we can restore later. >>>> + */ >>> >>> is_running must be disabled in between ...blocking and ...unblocking, >>> because we don't want to miss interrupts and block forever. >>> I somehow don't get it from the comment. :) >> >> Not sure if I understand your concern. However, the is_running bit >> setting/clearing should be handled in the avic_set_running below. This part >> only handles othe case when the is_running bit still set when calling >> vcpu_put (and later on loading some other vcpus). This way, when we are >> re-loading this vcpu, we can restore the is_running bit accordingly. > > I think that the comment is misleading. The saved is_running flag only > matters after svm_vcpu_blocking, yet the comment says that it handles > the irrelevant case before.
Actually, my understanding is if the svm_vcpu_blocking() is called, the is_running bit would have been cleared. At this point, if the vcpu is unloaded. We should not need to worry about it. Is that not the case here?
> Another minor bug is that was_running isn't initialized to 1, so we need > to halt before is_running gets set.
Just to make sure, you are referring to the point where the is_running is not set for first time the vcpu is loaded? If so, I agree. Thanks for the good catch.
> It would be clearer to toggle a flag in svm_vcpu_(un)blocking and set > is_running = !is_blocking.
Not sure what you meant here. We are already setting/unsetting the is_running bit when vcpu is blocking/unblocking. Are you suggesting just simply move the current avic_set_running() into the svm_vcpu_blocking and svm_vcpu_unblocking()?
> Doing so will also be immeasurably faster, > because avic_vcpu_load is called far more than svm_vcpu_(un)blocking.
Actually, this is not the same as handling normal vcpu blocking and unblocking, which we are already setting/un-setting the is_running bit in the avic_set_running(). The was_running should only be set to 1 if the vcpu is unloaded but has not yet calling halt.
Am I missing your points somehow?
Thanks, Suravee
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