On Tue, 01 Nov 2011, Anthony Liguori wrote: > On 11/01/2011 02:51 PM, Eric B Munson wrote: > >On Tue, 01 Nov 2011, Anthony Liguori wrote: > > > >>On 10/31/2011 03:07 PM, Eric B Munson wrote: > >>>The KVM_GUEST_PAUSED flag will prevent a guest from compaining about a soft > >>>lockup but it can mask real soft lockups if the flag isn't cleared when it is > >>>no longer relevant. This patch adds a kvm ioctl that the hypervisor will use > >>>when it resumes a guest to start a timer for aging out the flag. The time out > >>>will be specified by the hypervisor in the ioctl call. > >>> > >>>Signed-off-by: Eric B Munson<emunson@xxxxxxxxx> > >> > >>Why not have the guest clear the flag when it acknowledges it? > >> > >>The hypervisor would unconditionally set the bit, and the guest > >>would do a testandclear to check if the bit is set. I think that > >>avoids the whole aging business. > >> > >>Regards, > >> > >>Anthony Liguori > > > >If you have a look at patch 5 of this series, the flag is cleared when the > >guest checks the validity of a soft lockup. However, the aging is meant to > >cover the case where the guest never sees a soft lockup. We don't want this > >flag to be stored for ever and end up delaying real soft lockup messages. With > >that case in mind, I thought this was a good/simple compramise. > > If the guest clears the flag, then I don't think you have to worry about this. > > Regards, > > Anthony Liguori Except that the soft lockup doesn't trigger on every qemu "stop", only some of them. The flag isn't cleared until the detector is triggered. Eric
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