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Re: [Qemu-devel] [PATCH] Peek dont read for vmdescription
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH] Peek dont read for vmdescription |
Date: |
Tue, 23 Jun 2015 09:37:26 +0100 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
* Alexander Graf (address@hidden) wrote:
>
>
> On 22.06.15 16:49, Dr. David Alan Gilbert (git) wrote:
> > From: "Dr. David Alan Gilbert" <address@hidden>
> >
> > The VMDescription section maybe after the EOF mark, the current code
> > does a 'qemu_get_byte' and either gets the header byte identifying the
> > description or an error (which it ignores). Doing the 'get' upsets
> > RDMA which hangs on old machine types without the VMDescription.
> >
> > Using 'qemu_peek_byte' avoids that.
> >
> > Signed-off-by: Dr. David Alan Gilbert <address@hidden>
>
> Fun. I did actually use peek at first and then figured it's the same as
> read in the qemu file implementation. Have you figured out why exactly
> peek does make a difference for the RDMA case?
Hmm, no, I agree that is odd but I do need to look again at it.
I started off with a simple empty VM (no guest running) and found that
it wouldn't migrate over RDMA using machine types older than 2.3
unless I sent the vmdesc, and this seems to fix that for me.
However, I've found another case; a busy migrate running stressapp
that still fails on older machine types. My guess is that it depends
whether we've read the data already - if we're lucky and the data
is already in the qemu-file buffer it doesn't end up calling the RDMA
code again.
Dave
>
>
> Alex
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK