From: "Roedel, Joerg" <Joerg.Roedel@amd.com>
To: Zachary Amsden <zamsden@redhat.com>
Cc: Joerg Roedel <joro@8bytes.org>, Jan Kiszka <jan.kiszka@web.de>,
Avi Kivity <avi@redhat.com>,
Marcelo Tosatti <mtosatti@redhat.com>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>
Subject: Re: [PATCH 3/6] KVM: X86: Make tsc_delta calculation a function of guest tsc
Date: Tue, 19 Apr 2011 08:46:01 +0200 [thread overview]
Message-ID: <20110419064601.GM2192@amd.com> (raw)
In-Reply-To: <4DACD11B.4080200@redhat.com>
On Mon, Apr 18, 2011 at 08:02:35PM -0400, Zachary Amsden wrote:
> >
> > On Sat, Apr 16, 2011 at 06:09:17PM +0200, Jan Kiszka wrote:
> >
> >> On 2011-03-25 09:44, Joerg Roedel wrote:
> >>
> >
> >>> + tsc_delta = !vcpu->arch.last_guest_tsc ? 0 :
> >>> + tsc - vcpu->arch.last_guest_tsc;
> >>>
> >
> >> This patch appears to cause troubles to Linux guests on TSC clocksource
> >> and APIC highres timer. The first boot after qemu start is always fine,
> >> but after a reboot the guest timer appears to fire incorrectly or even
> >> not at all.
> >>
> >> Was this patch tested with a guest reboot scenario as well? Does it
> >> account for the TSC being reset to 0 on reboot?
> >>
> > Hmm, probably the last_guest_tsc is not updated correctly in this
> > scenario. I will have a look tomorrow.
> >
> > Joerg
> >
> >
>
> To avoid this problem, when the TSC is reset, the overshoot protection
> where last_guest_tsc is used is specifically disabled:
>
> /* Reset of TSC must disable overshoot protection below */
> vcpu->arch.hv_clock.tsc_timestamp = 0;
> vcpu->arch.last_tsc_write = data;
> vcpu->arch.last_tsc_nsec = ns;
>
> You can probably use the same test - last_guest_tsc is only valid if
> tsc_timestamp above != 0.
Yes, this should also work. But the other way we get rid of
last_host_tsc which is also a good thing :)
Joerg
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Registration: Dornach, Landkr. Muenchen; Registerger. Muenchen, HRB Nr. 43632
next prev parent reply other threads:[~2011-04-19 6:46 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-25 8:44 [PATCH 0/6] TSC scaling support for KVM v3 Joerg Roedel
2011-03-25 8:44 ` [PATCH 1/6] KVM: SVM: Implement infrastructure for TSC_RATE_MSR Joerg Roedel
2011-03-25 8:44 ` [PATCH 2/6] KVM: X86: Let kvm-clock report the right tsc frequency Joerg Roedel
2011-03-25 8:44 ` [PATCH 3/6] KVM: X86: Make tsc_delta calculation a function of guest tsc Joerg Roedel
2011-03-27 10:57 ` Avi Kivity
2011-03-27 11:10 ` Joerg Roedel
2011-04-16 16:09 ` Jan Kiszka
2011-04-17 12:06 ` Joerg Roedel
2011-04-19 0:02 ` Zachary Amsden
2011-04-19 6:46 ` Roedel, Joerg [this message]
2011-04-19 6:49 ` Jan Kiszka
2011-04-19 14:15 ` Zachary Amsden
2011-04-19 14:24 ` Jan Kiszka
2011-04-18 8:03 ` Roedel, Joerg
2011-04-18 9:12 ` Jan Kiszka
2011-04-18 9:25 ` Joerg Roedel
2011-03-25 8:44 ` [PATCH 4/6] KVM: X86: Implement call-back to propagate virtual_tsc_khz Joerg Roedel
2011-03-25 8:44 ` [PATCH 5/6] KVM: X86: Delegate tsc-offset calculation to architecture code Joerg Roedel
2011-03-25 8:44 ` [PATCH 6/6] KVM: X86: Implement userspace interface to set virtual_tsc_khz Joerg Roedel
2011-03-27 10:58 ` [PATCH 0/6] TSC scaling support for KVM v3 Avi Kivity
2011-04-06 7:33 ` Avi Kivity
-- strict thread matches above, loose matches on Subject: below --
2011-03-24 7:40 [PATCH 0/6][RESEND] TSC scaling support for KVM v2 Joerg Roedel
2011-03-24 7:40 ` [PATCH 3/6] KVM: X86: Make tsc_delta calculation a function of guest tsc Joerg Roedel
2011-03-15 9:36 [PATCH 0/6] TSC scaling support for KVM v2 Joerg Roedel
2011-03-15 9:36 ` [PATCH 3/6] KVM: X86: Make tsc_delta calculation a function of guest tsc Joerg Roedel
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