Messages in this thread | | | Subject | Re: [PATCH RFC 3/7] KVM: timer: synchronize tsc-deadline timestamp for guest | From | Quan Xu <> | Date | Thu, 14 Dec 2017 09:54:55 +0800 |
| |
On 2017/12/08 23:06, Konrad Rzeszutek Wilk wrote: > On Fri, Dec 08, 2017 at 04:39:46PM +0800, Quan Xu wrote: >> From: Ben Luo <bn0418@gmail.com> >> >> In general, KVM guest programs tsc-deadline timestamp to >> MSR_IA32_TSC_DEADLINE MSR. This will cause a VM-exit, and >> then KVM handles this timer for guest. >> >> The tsc-deadline timestamp is mostly recorded in share page >> with less VM-exit. We Introduce a periodically working kthread >> to scan share page and synchronize timer setting for guest >> on a dedicated CPU. > That sounds like a race. Meaning the guest may put too small window > and this 'working thread to scan' may not get to it fast enough? yes, you are right. So .. > . > Meaning we miss the deadline to inject the timer in the guest. > > Or is this part of this PV MSR semantics - that it will only work > for certain amount of values and anything less than say 1ms > should not use the PV MSR?
.. for these timers, We have to program these tsc-deadline timestamps to MSR_IA32_TSC_DEADLINE as normal, which will cause VM-exit and KVM will signal the working thread through IPI to program timer, instead of registering on current CPU (patch 0004).
more detail in patch 0007.
Quan Alibaba Cloud
| |