On 04/19/2012 03:00 PM, Jiri Denemark wrote: > 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 I'm hoping to actually drop this patch, and replace it with an alternative that calls set-block-job-speed _before_ block-stream or drive-mirror; but that depends on someone actually writing the qemu patch outlined in the thread here: https://lists.gnu.org/archive/html/qemu-devel/2012-04/msg02273.html At any rate, this serves as a good argument for why the qemu side of this patch series isn't quite ready to push to upstream libvirt yet. -- Eric Blake eblake@xxxxxxxxxx +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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