From: Avi Kivity <avi@qumranet.com>
To: Dan Hecht <dhecht@vmware.com>
Cc: Ingo Molnar <mingo@elte.hu>, Zachary Amsden <zach@vmware.com>,
jeremy@goop.org, avi@quramnet.com,
kvm-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org,
Glauber de Oliveira Costa <gcosta@redhat.com>,
Glauber de Oliveira Costa <glauber@qumranet.com>,
--cc@redhat.com, Garrett Smith <garrett@vmware.com>
Subject: Re: [kvm-devel] [PATCH] raise tsc clocksource rating
Date: Tue, 30 Oct 2007 06:24:56 +0200 [thread overview]
Message-ID: <4726B218.8010101@qumranet.com> (raw)
In-Reply-To: <47266B90.8000008@vmware.com>
Dan Hecht wrote:
> Not really. In the case hardware TSC is perfect, the paravirt time
> counter can be implemented directly in terms of hardware TSC; there is
> no loss in optimization. This is done transparently. And virtual TSC
> can be implemented this way too.
>
> The real improvement that a paravirt clocksource offers over the TSC
> clocksource is that the guest does not need to measure the TSC frequency
> itself against some other constant frequency source (which is
> problematic on a virtual machine). Instead, the paravirt clocksource
> queries the hypervisor for the frequency of the counter. As you know,
> with clocksource style kernels, it's important to get this frequency
> correct, or else the guest will have long-term time drift.
>
>
In addition, a paravirt clocksource can compensate for events like vcpu
migration to another host cpu. So I agree: a paravirt clocksource is
always better than or equal to the tsc.
--
Any sufficiently difficult bug is indistinguishable from a feature.
next prev parent reply other threads:[~2007-10-30 4:26 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-10-29 23:10 [PATCH] raise tsc clocksource rating Glauber de Oliveira Costa
2007-10-29 22:17 ` Thomas Gleixner
2007-10-29 22:36 ` Ingo Molnar
2007-10-30 1:26 ` john stultz
2007-10-30 2:39 ` Rusty Russell
2007-10-30 7:37 ` Ingo Molnar
2007-10-30 10:52 ` Rusty Russell
2007-10-30 12:13 ` Glauber de Oliveira Costa
2007-10-29 22:42 ` Zachary Amsden
2007-10-29 22:45 ` Jeremy Fitzhardinge
2007-10-29 22:48 ` Ingo Molnar
2007-10-29 22:52 ` Jeremy Fitzhardinge
2007-10-29 22:55 ` Ingo Molnar
2007-10-29 23:17 ` Jeremy Fitzhardinge
2007-10-29 23:21 ` Ingo Molnar
2007-10-29 23:33 ` Jeremy Fitzhardinge
2007-10-30 0:45 ` Ian Pratt
2007-10-30 7:19 ` Ingo Molnar
2007-10-29 22:55 ` Zachary Amsden
2007-10-29 23:02 ` Ingo Molnar
2007-10-29 23:13 ` Zachary Amsden
2007-10-29 23:17 ` Ingo Molnar
2007-10-30 12:02 ` Glauber de Oliveira Costa
2007-10-30 17:58 ` Zachary Amsden
2007-10-29 23:24 ` Dan Hecht
2007-10-30 4:24 ` Avi Kivity [this message]
2007-10-30 7:14 ` Ingo Molnar
2007-10-30 11:59 ` Glauber de Oliveira Costa
2007-10-30 0:17 ` H. Peter Anvin
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=4726B218.8010101@qumranet.com \
--to=avi@qumranet.com \
--cc=--cc@redhat.com \
--cc=avi@quramnet.com \
--cc=dhecht@vmware.com \
--cc=garrett@vmware.com \
--cc=gcosta@redhat.com \
--cc=glauber@qumranet.com \
--cc=jeremy@goop.org \
--cc=kvm-devel@lists.sourceforge.net \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@elte.hu \
--cc=zach@vmware.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 a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox