From: Joerg Roedel <joerg.roedel@amd.com>
To: Marcelo Tosatti <mtosatti@redhat.com>
Cc: <kvm@vger.kernel.org>, <zamsden@gmail.com>
Subject: Re: [patch 7/8] Dont mark TSC unstable due to S4 suspend
Date: Thu, 9 Feb 2012 15:28:59 +0100 [thread overview]
Message-ID: <20120209142859.GO22598@amd.com> (raw)
In-Reply-To: <20120208155646.GB3398@amt.cnet>
On Wed, Feb 08, 2012 at 01:56:46PM -0200, Marcelo Tosatti wrote:
> On Wed, Feb 08, 2012 at 04:18:48PM +0100, Joerg Roedel wrote:
> > This is not going to work when tsc-scaling is enabled. The
> > adjust_tsc_offset_host() function just scales the offset the same way
> > the tsc is scaled. But that is broken because the tsc-offset is applied
> > _after_ the tsc-ratio by scaling hardware. So to get the desired
> > tsc-value in the guest the offset needs to be scaled in the opposite
> > direction as the tsc itself. This is rather complicated to implement.
>
> By saying that "tsc-offset is applied _after_ the tsc-ratio by scaling
> hardware" you mean that guest tsc is calculated as
>
> tsc = host_tsc_value * tsc_ratio
> tsc += tsc_offset
>
> ?
>
> If so, that means the tsc_offset must be scaled to guest tsc units.
>
> Which is what both adjust_tsc_offset(host=true) and compute_tsc_offset()
> do.
>
> What am i missing here?
Nothing. You are right, bad math on my side.
Joerg
--
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next prev parent reply other threads:[~2012-02-09 14:29 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-03 17:43 [patch 0/8] KVM: Remaining body of TSC emulation work (Zachary Amsden) Marcelo Tosatti
2012-02-03 17:43 ` [patch 1/8] Infrastructure for software and hardware based TSC rate scaling Marcelo Tosatti
2012-02-08 14:28 ` Joerg Roedel
2012-02-03 17:43 ` [patch 2/8] Improve TSC offset matching Marcelo Tosatti
2012-02-03 17:43 ` [patch 3/8] Leave TSC synchronization window open with each new sync Marcelo Tosatti
2012-02-03 17:43 ` [patch 4/8] Fix last_guest_tsc / tsc_offset semantics Marcelo Tosatti
2012-02-03 17:43 ` [patch 5/8] Add last_host_tsc tracking back to KVM Marcelo Tosatti
2012-02-03 17:43 ` [patch 6/8] Allow adjust_tsc_offset to be in host or guest cycles Marcelo Tosatti
2012-02-03 17:43 ` [patch 7/8] Dont mark TSC unstable due to S4 suspend Marcelo Tosatti
2012-02-08 15:18 ` Joerg Roedel
2012-02-08 15:56 ` Marcelo Tosatti
2012-02-09 14:28 ` Joerg Roedel [this message]
2012-02-03 17:43 ` [patch 8/8] Track TSC synchronization in generations Marcelo Tosatti
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