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
--
AMD Operating System Research Center
Advanced Micro Devices GmbH Einsteinring 24 85609 Dornach
General Managers: Alberto Bozzo
Registration: Dornach, Landkr. Muenchen; Registerger. Muenchen, HRB Nr. 43632
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20120209142859.GO22598@amd.com \
--to=joerg.roedel@amd.com \
--cc=kvm@vger.kernel.org \
--cc=mtosatti@redhat.com \
--cc=zamsden@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.