[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] x86/time: update TSC stamp on restore from deep C-state
On 16/01/2020 09:38, Jan Beulich wrote: > On 16.01.2020 10:33, Roger Pau Monné wrote: >> On Wed, Jan 15, 2020 at 05:21:16PM +0100, Jan Beulich wrote: >>> On 15.01.2020 14:44, Roger Pau Monné wrote: >>>> On Wed, Jan 15, 2020 at 01:49:22PM +0100, Jan Beulich wrote: >>>>> What I'm then worried about is too >>>>> little progress observable by guests. The PV time protocol >>>>> ought to be fine in this regard (and consumers of raw TSC values >>>>> are on their own anyway), but wouldn't you need to update TSC >>>>> offsets of HVM guests in order to compensate for the elapsed >>>>> time? >>>> >>>> That will be done when the HVM vCPU gets scheduled in as part of the >>>> update_vcpu_system_time call AFAICT. cstate_restore_tsc will always be >>>> called with the idle vCPU context, and hence there's always going to >>>> be a vCPU switch before scheduling anything else. >>> >>> Which step would this be? All I see is a call to hvm_scale_tsc(). >>> In time.c only tsc_set_info() calls hvm_set_tsc_offset(). >> >> My bad, I've mistaken the scaling with the offset. >> >> Accounting for the offset in update_vcpu_system_time seems quite >> more complicated that just updating the TSC here, so: >> >> Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx> > > And then (preferably with "deep" dropped from the description, > if you, Igor, agree, and which can be done while committing) > Acked-by: Jan Beulich <jbeulich@xxxxxxxx> No objection. FYI I tested Roger's approach this night and it seems to work at least in sense of fixing the original issue. Igor _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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