At Thu, 05 Apr 2012 15:28:10 +0800, Liu Yuan wrote: > > On 03/31/2012 06:23 PM, Liu Yuan wrote: > > > On 03/31/2012 05:29 PM, MORITA Kazutaka wrote: > > > >> At Sat, 31 Mar 2012 15:34:10 +0800, > >> Liu Yuan wrote: > >>> > >>> On 03/31/2012 03:20 PM, MORITA Kazutaka wrote: > >>> > >>>> - Read requests: > >>>> read from a object cache always when the cache exists > >>>> > >>>> - Write requests: > >>>> flush and remove a object cache if SD_FLAG_CMD_CACHE is not set > >>>> > >>>> Isn't this okay for collie, too? > >>> > >>> > >>> Who set SD_FLAG_CMD_CACHE for collie? user or let collie decide itself? > >> > >> We don't need to set the same cache flag to the collie requests. > >> > >> Collie doesn't send write requests to the opened VDIs, so collie > >> doesn't flush the existing caches with my idea. > >> > > > I think this assumption is broken, collie vdi snapshot will do WRITE the > other's opened VDI.... The only way to take a snapshot of running VMs is a savevm command from the qemu monitor. We can use neither collie nor qemu-img for it. > > So collie vdi snapshot will simply remove the object cache of the victim > Guest... this is quite costy operation. > > So I'd like insisting that, we'd better not try to fix the bug that > should be fixed elsewhere. I think qemu-img convert should use > cache=passthrough mode, it is unfriendly for it to use writeback cache. It takes much longer time to convert VM disks with a writethrough mode. I'm not sure such change is acceptable for QEMU community. Thanks, Kazutaka |