Daniel Veillard wrote: > On Wed, Nov 09, 2011 at 09:29:23AM -0700, Eric Blake wrote: > >> This reverts commit ef1065cf5ac; see also this bug report: >> https://bugzilla.redhat.com/show_bug.cgi?id=751900 >> >> In qemu 0.15.1 and earlier, during migration to file, the >> qemu_savevm_state_begin and qemu_savevm_state_iterate methods >> will both process as much migration data as possible until either >> >> 1. The file descriptor returns EAGAIN >> 2. The bandwidth rate limit is reached >> >> If we set the rate limit to ULONG_MAX, test 2 never becomes true. We're >> passing a plain file descriptor to QEMU and POSIX does not support EAGAIN on >> regular files / block devices, so test 1 never becomes true either. >> >> In the 'virsh save --bypass-cache' case, we pass a pipe instead of a >> regular fd, but using a pipe adds I/O overhead, so always passing a >> pipe just so qemu can see EAGAIN doesn't seem nice. >> >> The ultimate fix needs to come from qemu - background migration must >> > > ACK, it's a bit of a shame, but until we have a fix, it's more > important to be able to abort a save to disk than to be able to save > at a speed of more than 32MB/s (if the storage system support this) > Agreed. BTW, I don't have access to the bug to see details, but I think I understand given Eric's description. Jim -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list