Stephane Eranian wrote: > Eddie, > > On Fri, Jul 13, 2007 at 08:46:06AM +0800, Dong, Eddie wrote: >> [EMAIL PROTECTED] wrote: >>> Avi, >>> >>> A couple of months back, we had a discussion about PMU >>> virtualization and the difficulty I encountered trying to catch the >>> PMU interrupt vector in kvm on VM-exit. KVM does not set >>> ack_intr_on_intr. Would you mind reminding me of the reason for >>> this? >>> >>> On the topic of scheduler hooks for use by KVM, I think this >>> would help me also because it means I would not have to save >>> and restore the PMU registers on all VM-exit/VM-entry. At least >> >> W/o the hook, the PMU save/restore can be done in heavy weight >> VM Exit path, the majority of VM Exit are light weight which doesn't >> need to do if you don't care the cycles spent in KVM. >> refer vmx_vcpu_put & vmx_vcpu_load. >> > I am not sure I understand your terminology about heavy vs. light.
Hi, Stephane: Sorry for the confuse. Heavy weight VM exit here means a VM Exit which may cause context switch, while light weight VM Exit doesn't. We already have some lazy MSR save/restore stuff which is only for heavy weight VM Exit such as MSR_CSTAR save/restore. > > You do need to stop monitoring on every VM-exit, because you do not > want to continue measuring while in KVM. On VM-entry, then you need > to re-activate. So you can use explcit code to clear a bunch of > MSR on VM-exit and restore them on VM-entry. Alternatively, you > can use (on VT-x, not on AMD-v) the VT-x feature to automatically > save and restore MSRs on VM-exit/VM-entry. All of this can be done > lazily, i.e., only once you start using the PMU. Yes. > > On VM-exit, which leads to context switch of the KVM thread, then > you do need to do more work and save the PMU counters. That would > have to be done by software given that VT-x does not know about > Linux context switching. This is where the hooks come in handy. > Same thing on context switch in. Yes. But without the hook, this save/restore is only needed for heavy weight VM Exit. > >> With hook, then we can further reduce the save/restore effort :-) Yes, that serve us much better :-) Thx, eddie ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
