On Fri, Mar 02, 2018 at 11:20:55AM -0500, John Snow wrote: > > > On 03/02/2018 10:39 AM, Eric Blake wrote: > > On 02/26/2018 08:05 PM, Liang Li wrote: > >> When doing drive mirror to a low speed shared storage, if there was heavy > >> BLK IO write workload in VM after the 'ready' event, drive mirror > >> block job > >> can't be canceled immediately, it would keep running until the heavy > >> BLK IO > >> workload stopped in the VM. > >> > >> Libvirt depends on the current block-job-cancel semantics, which is that > >> when used without a flag after the 'ready' event, the command blocks > >> until data is in sync. However, these semantics are awkward in other > >> situations, for example, people may use drive mirror for realtime > >> backups while still wanting to use block live migration. Libvirt cannot > >> start a block live migration while another drive mirror is in progress, > >> but the user would rather abandon the backup attempt as broken and > >> proceed with the live migration than be stuck waiting for the current > >> drive mirror backup to finish. > >> > >> The drive-mirror command already includes a 'force' flag, which libvirt > >> does not use, although it documented the flag as only being useful to > >> quit a job which is paused. However, since quitting a paused job has > >> the same effect as abandoning a backup in a non-paused job (namely, the > >> destination file is not in sync, and the command completes immediately), > >> we can just improve the documentation to make the force flag obviously > >> useful. > > > > How does this interact with John's ongoing work to redo block job > > semantics: > > https://lists.gnu.org/archive/html/qemu-devel/2018-02/msg06167.html > > > >> > >> Cc: Paolo Bonzini <pbonz...@redhat.com> > >> Cc: Jeff Cody <jc...@redhat.com> > >> Cc: Kevin Wolf <kw...@redhat.com> > >> Cc: Max Reitz <mre...@redhat.com> > >> Cc: Eric Blake <ebl...@redhat.com> > >> Cc: John Snow <js...@redhat.com> > >> Reported-by: Huaitong Han <huanhuait...@didichuxing.com> > >> Signed-off-by: Huaitong Han <huanhuait...@didichuxing.com> > >> Signed-off-by: Liang Li <liliang...@didichuxing.com> > >> --- > > > > But in isolation, the patch looks reasonable to me. > > > > Reviewed-by: Eric Blake <ebl...@redhat.com> > > > > In fairness, this patch hit the list before mine did, so... > > I think it'll be OK to accommodate -- I think. It just changes the > nature of how fast the cancellation happens in mirror, which shouldn't > muck around with the general flow of job management in general. I think. > > Famous last words. >
I think Kevin's pulled your series in through his branch, and this patch conflicts with it. Do we want to try to rebase this patch on top of your series?
