[libvirt] [PATCH] qemu: Use unlimited speed when migrating to file

[Eric Blake]

On 03/21/2012 08:11 AM, Jiri Denemark wrote:
> This reverts commit 61f2b6ba5fdef0613d6351b99913b5ef468144ce and most of
> commit d8916dc8e2f612ab3ce46f32c4bfeb0bd73f6007, which effectively
> brings back commit ef1065cf5acad13767c054758cbe7f4e8af5d241 written by
> Jim Fehlig:

That history makes it look like we can't make up our minds :)  But also
important in the churn is indeed the intermediate changes to our
migration code passing in a pipe, and improvements in qemu.

> 
> The qemu migration speed default is 32MiB/s as defined in migration.c
> 
> /* Migration speed throttling */
> static int64_t max_throttle = (32 << 20);
> 
> There's no need to throttle migration when targeting a file, so set
> migration speed to unlimited prior to migration, and restore to libvirt
> default value after migration.
> 
> Default units is MB for migrate_set_speed monitor command, so
> (INT64_MAX / (1024 * 1024)) is used for unlimited migration speed.
> 
> This was reverted because migration to file could not be canceled and
> even monitored since qemu were not processing any monitor commands until
> the migration finished. This is now different as we make sure the
> file descriptor we pass to qemu is able to properly report EAGAIN.
> Recent qemu changes might have helped as well.
> 
> I tested managedsave with this patch in and indeed, it is 10x faster
> while I can still monitor its progress.
> ---
>  src/qemu/qemu_domain.h    |    7 +++++++
>  src/qemu/qemu_migration.c |   17 +++++++++++++++++
>  2 files changed, 24 insertions(+), 0 deletions(-)

ACK.

-- 
Eric Blake   eblake at redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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