From: Andi Kleen <andi@firstfloor.org>
To: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Anthony Liguori <anthony@codemonkey.ws>,
Avi Kivity <avi@qumranet.com>,
kvm@vger.kernel.org, John Stultz <johnstul@us.ibm.com>,
"Yang, Sheng" <sheng.yang@intel.com>
Subject: Re: [patch 0/7] force the TSC unreliable by reporting C2 state
Date: Fri, 20 Jun 2008 16:07:14 +0200 [thread overview]
Message-ID: <87tzfo9p4d.fsf@basil.nowhere.org> (raw)
In-Reply-To: <20080618224118.GA23236@dmt.cnet> (Marcelo Tosatti's message of "Wed, 18 Jun 2008 19:41:18 -0300")
Marcelo Tosatti <mtosatti@redhat.com> writes:
>
> Well, Linux assumes that TSC stops ticking on C2/C3.
It doesn't always and Linux is overly conservative and doesn't know
the full rules (and in some cases it's also hard to know because the
BIOS hides systems). Also a lot of systems don't have C2/C3.
But it still happens occasionally so it has to be handled. Normally
we would expect guests to detect this because they have exactly the
same problem on real hardware, but at least older Linux didn't always
get it correct.
But in general the newer kernel already keeps an estimate on how long C2/C3 took
(needed for power management) and nobody would stop KVM from just adding
that into the TSC offset that is supported by VT. You might still have some drift
from that though.
-Andi
prev parent reply other threads:[~2008-06-20 14:08 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-06-18 16:42 [patch 0/7] force the TSC unreliable by reporting C2 state Marcelo Tosatti
2008-06-18 16:42 ` [patch 1/7] kvm: qemu: inform valid C2 state in ACPI table Marcelo Tosatti
2008-06-18 16:42 ` [patch 2/7] kvm: qemu: disable c2 via _CST notification Marcelo Tosatti
2008-06-18 16:42 ` [patch 3/7] libkvm: in-kernel C2 halt interface Marcelo Tosatti
2008-06-18 16:42 ` [patch 4/7] libkvm: handle_io return handler value Marcelo Tosatti
2008-06-18 16:42 ` [patch 5/7] qemu: kvm: unhalt vcpu0 on pit irq Marcelo Tosatti
2008-06-18 16:42 ` [patch 6/7] kvm: qemu: enable in-kernel C2 emulation / userspace emulation Marcelo Tosatti
2008-06-18 16:42 ` [patch 7/7] KVM: in-kernel ACPI C2 idle emulation Marcelo Tosatti
2008-06-23 3:01 ` Avi Kivity
2008-06-18 20:09 ` [patch 0/7] force the TSC unreliable by reporting C2 state Anthony Liguori
2008-06-18 20:40 ` Marcelo Tosatti
2008-06-18 21:02 ` Anthony Liguori
2008-06-18 21:21 ` Marcelo Tosatti
2008-06-18 21:42 ` Anthony Liguori
2008-06-18 22:41 ` Marcelo Tosatti
2008-06-18 22:57 ` john stultz
2008-06-18 23:08 ` Nakajima, Jun
2008-06-20 14:07 ` Andi Kleen [this message]
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