From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Jon Kohler <jon@nutanix.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"x86@kernel.org" <x86@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Sean Christopherson <seanjc@google.com>
Subject: Re: [PATCH] KVM: X86: correct trace_kvm_pv_tlb_flush stats
Date: Thu, 05 May 2022 10:09:56 +0200 [thread overview]
Message-ID: <87h7641ju3.fsf@redhat.com> (raw)
In-Reply-To: <8E192C0D-512C-4030-9EBE-C0D6029111FE@nutanix.com>
Jon Kohler <jon@nutanix.com> writes:
>> On May 4, 2022, at 5:47 PM, Sean Christopherson <seanjc@google.com> wrote:
>>
...
>
> The net problem here is really that the stat is likely incorrect; however,
> one other oddity I didn’t quite understand after looking into this is that
> the call site for all of this is in record_steal_time(), which is only called
> from vcpu_enter_guest(), and that is called *after*
> kvm_service_local_tlb_flush_requests(), which also calls
> kvm_vcpu_flush_tlb_guest() if request == KVM_REQ_TLB_FLUSH_GUEST
>
> That request may be there set from a few different places.
>
> I don’t have any proof of this, but it seems to me like we might have a
> situation where we double flush?
>
> Put another way, I wonder if there is any sense behind maybe hoisting
> if (kvm_check_request(KVM_REQ_STEAL_UPDATE, vcpu)) up before
> Other tlb flushes, and have it clear the FLUSH_GUEST if it was set?
Indeed, if we move KVM_REQ_STEAL_UPDATE check/record_steal_time() call
in vcpu_enter_guest() before kvm_service_local_tlb_flush_requests(), we
can probably get aways with kvm_make_request(KVM_REQ_TLB_FLUSH_GUEST,
vcpu) in record_steal_time() which would help to avoid double flushing.
--
Vitaly
next prev parent reply other threads:[~2022-05-05 8:11 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-04 18:27 [PATCH] KVM: X86: correct trace_kvm_pv_tlb_flush stats Jon Kohler
2022-05-04 21:47 ` Sean Christopherson
2022-05-05 0:26 ` Jon Kohler
2022-05-05 8:09 ` Vitaly Kuznetsov [this message]
2022-05-06 15:42 ` Jon Kohler
2022-05-10 7:57 ` Vitaly Kuznetsov
2022-05-10 13:38 ` Sean Christopherson
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