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Re: [libvirt] [PATCHv5 12/23] blockjob: relax block job behavior when setting speed up front



On Mon, Apr 16, 2012 at 23:06:03 -0600, Eric Blake wrote:
> In qemu, it is possible to call 'migrate_set_speed' prior to
> 'migrate', and therefore ensure a constant throttling through the
> entire migration.  However, this is not possible with
> 'block-job-set-speed', which fails if a job is not already active.
> This means that you can't detect a device that doesn't support
> throttling until after you have already started a block job and
> let an unknown amount of unthrottled data through.  Aborting the
> job upon failure to set the speed seems a bit harsh, since it
> would have been nicer to prevent the job from starting in the
> first place, rather than letting an unknown amount of data be
> processed before detecting the speed failure.  So I propose
> relaxing the documentation, and explicitly mentioning that setting
> the speed is a best-effort attempt that might be ignored.  On the
> other hand, I've also requested that qemu consider adding an
> optional parameter to allow setting the speed at the creation of a
> block job.
> 
> * src/libvirt.c (virDomainBlockPull, virDomainBlockRebase): Update
> the documentation.
> * src/qemu/qemu_driver.c (qemuDomainBlockJobImpl)
> (qemuDomainBlockCopy): Log but don't fail when speed change fails.
> ---
> 
> v5: new patch; see also this qemu request:
> https://lists.gnu.org/archive/html/qemu-devel/2012-04/msg02185.html
> 
>  src/libvirt.c          |   12 ++++++++++--
>  src/qemu/qemu_driver.c |   18 ++++++++++++------
>  2 files changed, 22 insertions(+), 8 deletions(-)

OK

Jirka


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