Re: [Qemu-devel] [libvirt] speeding up qemu core dumps

[Daniel P. Berrange]

On Wed, Aug 03, 2011 at 09:42:23PM -0600, Jim Fehlig wrote:
> Eric Blake wrote:
> > On 08/03/2011 08:37 AM, Jim Fehlig wrote:
> >> http://lists.nongnu.org/archive/html/qemu-devel/2011-02/msg01156.html
> >>
> >> I thought there were more discussions on the topic but can only find the
> >> above thread ATM.
> >>
> >> Do folks here have objections to increasing the migration speed prior to
> >> core dump?  If not, any suggestions for a value?  I set the migration
> >> speed to 1G in doCoreDump() prior to calling qemuMigrationToFile() with
> >> following improvement dumping a 4G guest
> >
> > Why any limit at all?  When dumping to file rather than network, I
> > can't think of any justification for a default limit when targetting a
> > local drive (a particular installation may have a reasonable limit,
> > especially if the file involved happens to use a network - think
> > NFS).  It seems like it would make sense to override the qemu defaults
> > and go with unlimited speed for faster dump and save operations.
> 
> Agreed, 1G was just a test value, but I'm haven't yet figured out how to
> define unlimited.  From libvirt json monitor connection I tried
> migrate_set_speed with INT64_MAX, but that was invalid.  Using qemu
> monitor directly, I can go as high as INT64_MAX-512
> 
> (qemu) migrate_set_speed 9223372036854775295B
> (qemu) migrate_set_speed 9223372036854775296B
> invalid size
> 
> Any hints on proper way to set unlimited migration speed?

The code doesn't seem to have a way to set a truely unlimited rate,
but even INT64_MAX / 2 would be more than sufficient for us to max
out the host OS storage throughput


Daniel
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