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From: Anthony Liguori <anthony@codemonkey.ws>
To: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Avi Kivity <avi@qumranet.com>, kvm@vger.kernel.org
Subject: Re: [patch 0/7] force the TSC unreliable by reporting C2 state
Date: Wed, 18 Jun 2008 15:09:41 -0500	[thread overview]
Message-ID: <48596B85.7090008@codemonkey.ws> (raw)
In-Reply-To: <20080618164205.108219607@localhost.localdomain>

Marcelo Tosatti wrote:
> Avi, I don't think this causes such a huge performance regression. NOHZ
> makes the frequency of timer reads go down significantly.
>   

Have we yet determined why the TSC is so unstable in the first place?  
In theory, it should be relatively stable on single-node Intel and 
Barcelona chips.

Regards,

Anthony Liguori

> As for constant tick guests, well, the impact will be similar to
> changing to SMP, since those fallback to ACPI timer anyway now.
>
> The C2 emulation is required by Ubuntu 7.10 for example, which refuses
> to process the CST notification.
>
> Stock Linux kernels (as old as 2.6.20) do mark C2 invalid upon the CST
> notification.
>
>   


  parent reply	other threads:[~2008-06-18 20:10 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 ` Anthony Liguori [this message]
2008-06-18 20:40   ` [patch 0/7] force the TSC unreliable by reporting C2 state 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

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