> -----邮件原件----- > 发件人: Like Xu [mailto:[email protected]] > 发送时间: 2020年6月5日 13:29 > 收件人: Li,Rongqing <[email protected]>; [email protected] > 抄送: [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected] > 主题: Re: 答复: [PATCH][v6] KVM: X86: support APERF/MPERF registers > > On 2020/6/5 12:23, Li,Rongqing wrote: > > > > > >> -----邮件原件----- > >> 发件人: Xu, Like [mailto:[email protected]] > >> 发送时间: 2020年6月5日 10:32 > >> 收件人: Li,Rongqing <[email protected]> > >> 抄送: [email protected]; [email protected]; > >> [email protected]; [email protected]; [email protected]; [email protected]; > >> [email protected]; [email protected]; [email protected]; > >> [email protected]; [email protected]; > >> [email protected]; [email protected]; [email protected] > >> 主题: Re: [PATCH][v6] KVM: X86: support APERF/MPERF registers > >> > >> Hi RongQing, > >> > >> On 2020/6/5 9:44, Li RongQing wrote: > >>> Guest kernel reports a fixed cpu frequency in /proc/cpuinfo, this is > >>> confused to user when turbo is enable, and aperf/mperf can be used > >>> to show current cpu frequency after 7d5905dc14a > >>> "(x86 / CPU: Always show current CPU frequency in /proc/cpuinfo)" > >>> so guest should support aperf/mperf capability > >>> > >>> This patch implements aperf/mperf by three mode: none, software > >>> emulation, and pass-through > >>> > >>> None: default mode, guest does not support aperf/mperf > >> s/None/Note > >>> > >>> Software emulation: the period of aperf/mperf in guest mode are > >>> accumulated as emulated value > >>> > >>> Pass-though: it is only suitable for KVM_HINTS_REALTIME, Because > >>> that hint guarantees we have a 1:1 vCPU:CPU binding and guaranteed > >>> no over-commit. > >> The flag "KVM_HINTS_REALTIME 0" (in the > >> Documentation/virt/kvm/cpuid.rst) is claimed as "guest checks this > >> feature bit to determine that vCPUs are never preempted for an unlimited > time allowing optimizations". > >> > >> I couldn't see its relationship with "1:1 vCPU: pCPU binding". > >> The patch doesn't check this flag as well for your pass-through purpose. > >> > >> Thanks, > >> Like Xu > > > > > > I think this is user space jobs to bind HINT_REALTIME and mperf passthrough, > KVM just do what userspace wants. > > > > That's fine for user space to bind HINT_REALTIME and mperf passthrough， > But I was asking why HINT_REALTIME means "1:1 vCPU: pCPU binding". > > As you said, "Pass-though: it is only suitable for KVM_HINTS_REALTIME", which > means, KVM needs to make sure the kvm->arch.aperfmperf_mode value could > "only" be set to KVM_APERFMPERF_PT when the check > kvm_para_has_hint(KVM_HINTS_REALTIME) is passed. >
pining vcpu can ensure that guest get correct mperf/aperf, but a user has the choice to not pin, at that condition, do not think it is bug, this wants to say > Specifically, the KVM_HINTS_REALTIME is a per-kvm capability while the > kvm_aperfmperf_mode is a per-vm capability. It's unresolved. > Do you have any solution? -Rongqing > KVM doesn't always do what userspace wants especially you're trying to > expose some features about power and thermal management in the > virtualization context. > > > and this gives user space a possibility, guest has passthrough > > mperfaperf without HINT_REALTIME, guest can get coarse cpu frequency > > without performance effect if guest can endure error frequency > > occasionally > > > > > > > > -Li > >
