From: Blue Swirl <blauwirbel@gmail.com>
To: Uri Lublin <uril@redhat.com>
Cc: Glauber Costa <glommer@redhat.com>, Dor Laor <dlaor@redhat.com>,
qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH] ram_save_live: add a no-progress convergence rule
Date: Wed, 20 May 2009 20:28:45 +0300 [thread overview]
Message-ID: <f43fc5580905201028j41549a85v733499ce59a2b5fb@mail.gmail.com> (raw)
In-Reply-To: <4A143659.6050108@redhat.com>
On 5/20/09, Uri Lublin <uril@redhat.com> wrote:
> On 05/19/2009 09:17 PM, Anthony Liguori wrote:
>
> > Glauber Costa wrote:
> >
> > > On Tue, May 19, 2009 at 05:59:14PM +0300, Dor Laor wrote:
> > >
> > >
> > > > We can also make it configurable using the monitor migrate command.
> > > > For example:
> > > > migrate -d -no_progress -threshold=x tcp:....
> > > >
> > > it can be done, but it fits better as a different monitor command
> > >
> > > anthony, do you have any strong opinions here, or is this scheme
> > > acceptable?
> > >
> >
> > Threshold is a bad metric. There's no way to choose a right number. If
> > we were going to have a means to support metrics-based forced
> > convergence (and I really think this belongs in libvirt) I'd rather see
> > something based on bandwidth or wall clock time.
> >
> > Let me put it this way, why 50? What were the guidelines for choosing
> > that number and how would you explain what number a user should choose?
> >
>
> I've changed the threshold of the first convergence rule, to 50 from 10.
> Why 10 ? For this rule the threshold (number of dirty pages) and the number
> of bytes to transfer are equivalent.
>
> 50 pages is about 200K, which can be still sent quickly.
> I've added debug messages and noticed we never hit a number smaller than 10
> (excluding 0). The truth is there were very little number of runs with less
> than 50 dirty pages too. I don't mind leaving it at 10 (should be
> configurable too).
>
> For the second migration convergence rule I've set the limit to 10, as it
> seems much larger than what I've needed (all the runs I've made a number of
> 2-4 no-progress iterations was good enough, as it seems to have a repetitive
> behavior later), but I've enlarged it "just in case". No real research work
> was done here.
>
> Note that a no-progress iteration depends on both network bandwidth and
> guest actions.
Instead of freezing the guest or aborting the migration, the guest
could be throttled a bit by giving it less CPU time relative to
migration, or by incurring a small delay for each page dirtying write
access. Maybe this method would find the balance faster.
next prev parent reply other threads:[~2009-05-20 17:28 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-05-19 11:09 [Qemu-devel] [PATCH] ram_save_live: add a no-progress convergence rule Uri Lublin
2009-05-19 13:00 ` Anthony Liguori
2009-05-19 14:41 ` Glauber Costa
2009-05-19 14:59 ` Dor Laor
2009-05-19 15:09 ` Glauber Costa
2009-05-19 18:17 ` Anthony Liguori
2009-05-20 16:56 ` Uri Lublin
2009-05-20 17:28 ` Blue Swirl [this message]
2009-05-20 17:34 ` Uri Lublin
2009-05-19 18:19 ` Anthony Liguori
2009-05-19 18:15 ` Anthony Liguori
2009-05-20 17:17 ` Uri Lublin
2009-05-19 18:09 ` Anthony Liguori
2009-05-20 17:25 ` Uri Lublin
2009-05-20 17:15 ` Daniel P. Berrange
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=f43fc5580905201028j41549a85v733499ce59a2b5fb@mail.gmail.com \
--to=blauwirbel@gmail.com \
--cc=dlaor@redhat.com \
--cc=glommer@redhat.com \
--cc=qemu-devel@nongnu.org \
--cc=uril@redhat.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;
as well as URLs for NNTP newsgroup(s).