[libvirt] [PATCH 2/2] Adjust block size used by dd to speed QEMU domain save operations.

[Laine Stump]

See https://bugzilla.redhat.com/show_bug.cgi?id=599091

Saving a paused 512MB domain took 3m47s with the old block size of 512
bytes. Changing the block size to 1024*1024 decreased the time to 56
seconds. (Doubling again to 2048*1024 yielded 0 improvement; lowering
to 512k increased the save time to 1m10s, about 20%)
---
 src/qemu/qemu_monitor.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/src/qemu/qemu_monitor.h b/src/qemu/qemu_monitor.h
index 1870b22..fd39b1c 100644
--- a/src/qemu/qemu_monitor.h
+++ b/src/qemu/qemu_monitor.h
@@ -261,7 +261,7 @@ int qemuMonitorMigrateToCommand(qemuMonitorPtr mon,
                                 unsigned int background,
                                 const char * const *argv);
 
-# define QEMU_MONITOR_MIGRATE_TO_FILE_BS 512llu
+# define QEMU_MONITOR_MIGRATE_TO_FILE_BS (1024llu * 2048)
 
 int qemuMonitorMigrateToFile(qemuMonitorPtr mon,
                              unsigned int background,
-- 
1.7.0.1