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Wed, 31 Jul 2024 01:03:21 +0000 Date: Wed, 31 Jul 2024 09:03:10 +0800 From: Chao Gao To: Suleiman Souhlal CC: Suleiman Souhlal , Sean Christopherson , Paolo Bonzini , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , , "H. Peter Anvin" , , Subject: Re: [PATCH] KVM: x86: Include host suspended time in steal time. 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>> >> Is it possible that a vCPU doesn't get any chance to run (i.e., update steal >> time) between two suspends? In this case, only the second suspend would be >> recorded. > >Good point. I'll address this. > >> >> Maybe we need an infrastructure in the PM subsystem to record accumulated >> suspended time. When updating steal time, KVM can add the additional suspended >> time since the last update into steal_time (as how KVM deals with >> current->sched_info.run_deley). This way, the scenario I mentioned above won't >> be a problem and KVM needn't calculate the suspend duration for each guest. And >> this approach can potentially benefit RISC-V and ARM as well, since they have >> the same logic as x86 regarding steal_time. > >Thanks for the suggestion. >I'm a bit wary of making a whole PM subsystem addition for such a counter, but >maybe I can make a architecture-independent KVM change for it, with a PM >notifier in kvm_main.c. Sounds good. > >> >> Additionally, it seems that if a guest migrates to another system after a suspend >> and before updating steal time, the suspended time is lost during migration. I'm >> not sure if this is a practical issue. > >The systems where the host suspends don't usually do VM migrations. Or at least >the ones where we're encountering the problem this patch is trying to address >don't (laptops). >But even if they did, it doesn't seem that likely that the migration would >happen over a host suspend. >If it's ok with you, I'll put this issue aside for the time being. I am fine with putting this issue aside.