[libvirt] [RFC PATCH] libvirt support to force convergence of live guest migration

[Chegu Vinod]

Busy enterprise workloads hosted on large sized VM's tend to dirty
memory faster than the transfer rate achieved via live guest migration.
Despite some good recent improvements (& using dedicated 10Gig NICs
between hosts) the live migration may NOT converge.

Recently support was added in qemu (version 1.6) to allow a user to
choose if they wish to force convergence of their migration via a
new migration capability : "auto-converge". This feature allows for qemu
to auto-detect lack of convergence and trigger a throttle-down of the
VCPUs. 

This RFC patch includes the libvirt support needed to trigger this
feature. (Testing is still in progress)

Signed-off-by:  Chegu Vinod <chegu_vinod at hp.com>
---
 include/libvirt/libvirt.h.in |    1 +
 src/qemu/qemu_migration.c    |   44 ++++++++++++++++++++++++++++++++++++++++++
 src/qemu/qemu_migration.h    |    1 +
 src/qemu/qemu_monitor.c      |    2 +-
 src/qemu/qemu_monitor.h      |    1 +
 tools/virsh-domain.c         |    7 ++++++
 6 files changed, 55 insertions(+), 1 deletions(-)

diff --git a/include/libvirt/libvirt.h.in b/include/libvirt/libvirt.h.in
index 146a59b..13b0bfc 100644
--- a/include/libvirt/libvirt.h.in
+++ b/include/libvirt/libvirt.h.in
@@ -1192,6 +1192,7 @@ typedef enum {
     VIR_MIGRATE_OFFLINE           = (1 << 10), /* offline migrate */
     VIR_MIGRATE_COMPRESSED        = (1 << 11), /* compress data during migration */
     VIR_MIGRATE_ABORT_ON_ERROR    = (1 << 12), /* abort migration on I/O errors happened during migration */
+    VIR_MIGRATE_AUTO_CONVERGE     = (1 << 13), /* force auto-convergence during during migration */
 } virDomainMigrateFlags;
 
 
diff --git a/src/qemu/qemu_migration.c b/src/qemu/qemu_migration.c
index e87ea85..8cc0c56 100644
--- a/src/qemu/qemu_migration.c
+++ b/src/qemu/qemu_migration.c
@@ -1565,6 +1565,40 @@ cleanup:
 }
 
 static int
+qemuMigrationSetAutoConverge(virQEMUDriverPtr driver,
+                            virDomainObjPtr vm,
+                            enum qemuDomainAsyncJob job)
+{
+    qemuDomainObjPrivatePtr priv = vm->privateData;
+    int ret;
+
+    if (qemuDomainObjEnterMonitorAsync(driver, vm, job) < 0)
+        return -1;
+
+    ret = qemuMonitorGetMigrationCapability(
+                priv->mon,
+                QEMU_MONITOR_MIGRATION_CAPS_AUTO_CONVERGE);
+
+    if (ret < 0) {
+        goto cleanup;
+    } else if (ret == 0) {
+            virReportError(VIR_ERR_ARGUMENT_UNSUPPORTED, "%s",
+                           _("Auto-Converge migration is not supported by "
+                             "QEMU binary"));
+        ret = -1;
+        goto cleanup;
+    }
+
+    ret = qemuMonitorSetMigrationCapability(
+                priv->mon,
+                QEMU_MONITOR_MIGRATION_CAPS_AUTO_CONVERGE);
+
+cleanup:
+    qemuDomainObjExitMonitor(driver, vm);
+    return ret;
+}
+
+static int
 qemuMigrationWaitForSpice(virQEMUDriverPtr driver,
                           virDomainObjPtr vm)
 {
@@ -2389,6 +2423,11 @@ qemuMigrationPrepareAny(virQEMUDriverPtr driver,
                                     QEMU_ASYNC_JOB_MIGRATION_IN) < 0)
         goto stop;
 
+    if (flags & VIR_MIGRATE_AUTO_CONVERGE &&
+        qemuMigrationSetAutoConverge(driver, vm,
+                                    QEMU_ASYNC_JOB_MIGRATION_IN) < 0)
+        goto stop;
+
     if (mig->lockState) {
         VIR_DEBUG("Received lockstate %s", mig->lockState);
         VIR_FREE(priv->lockState);
@@ -3181,6 +3220,11 @@ qemuMigrationRun(virQEMUDriverPtr driver,
                                     QEMU_ASYNC_JOB_MIGRATION_OUT) < 0)
         goto cleanup;
 
+    if (flags & VIR_MIGRATE_AUTO_CONVERGE &&
+        qemuMigrationSetAutoConverge(driver, vm,
+                                    QEMU_ASYNC_JOB_MIGRATION_OUT) < 0)
+        goto cleanup;
+
     if (qemuDomainObjEnterMonitorAsync(driver, vm,
                                        QEMU_ASYNC_JOB_MIGRATION_OUT) < 0)
         goto cleanup;
diff --git a/src/qemu/qemu_migration.h b/src/qemu/qemu_migration.h
index cafa2a2..c4258a1 100644
--- a/src/qemu/qemu_migration.h
+++ b/src/qemu/qemu_migration.h
@@ -39,6 +39,7 @@
      VIR_MIGRATE_UNSAFE |                       \
      VIR_MIGRATE_OFFLINE |                      \
      VIR_MIGRATE_COMPRESSED |                   \
+     VIR_MIGRATE_AUTO_CONVERGE |                \
      VIR_MIGRATE_ABORT_ON_ERROR)
 
 /* All supported migration parameters and their types. */
diff --git a/src/qemu/qemu_monitor.c b/src/qemu/qemu_monitor.c
index 1514715..780a29a 100644
--- a/src/qemu/qemu_monitor.c
+++ b/src/qemu/qemu_monitor.c
@@ -118,7 +118,7 @@ VIR_ENUM_IMPL(qemuMonitorMigrationStatus,
 
 VIR_ENUM_IMPL(qemuMonitorMigrationCaps,
               QEMU_MONITOR_MIGRATION_CAPS_LAST,
-              "xbzrle")
+              "xbzrle", "auto-converge")
 
 VIR_ENUM_IMPL(qemuMonitorVMStatus,
               QEMU_MONITOR_VM_STATUS_LAST,
diff --git a/src/qemu/qemu_monitor.h b/src/qemu/qemu_monitor.h
index eabf000..95e70ab 100644
--- a/src/qemu/qemu_monitor.h
+++ b/src/qemu/qemu_monitor.h
@@ -440,6 +440,7 @@ int qemuMonitorGetSpiceMigrationStatus(qemuMonitorPtr mon,
 
 typedef enum {
     QEMU_MONITOR_MIGRATION_CAPS_XBZRLE,
+    QEMU_MONITOR_MIGRATION_CAPS_AUTO_CONVERGE,
 
     QEMU_MONITOR_MIGRATION_CAPS_LAST
 } qemuMonitorMigrationCaps;
diff --git a/tools/virsh-domain.c b/tools/virsh-domain.c
index 1fe138c..d94a81b 100644
--- a/tools/virsh-domain.c
+++ b/tools/virsh-domain.c
@@ -8532,6 +8532,10 @@ static const vshCmdOptDef opts_migrate[] = {
      .type = VSH_OT_BOOL,
      .help = N_("compress repeated pages during live migration")
     },
+    {.name = "auto-converge",
+     .type = VSH_OT_BOOL,
+     .help = N_("force auto convergence during live migration")
+    },
     {.name = "abort-on-error",
      .type = VSH_OT_BOOL,
      .help = N_("abort on soft errors during migration")
@@ -8676,6 +8680,9 @@ doMigrate(void *opaque)
     if (vshCommandOptBool(cmd, "compressed"))
         flags |= VIR_MIGRATE_COMPRESSED;
 
+    if (vshCommandOptBool(cmd, "auto-converge"))
+        flags |= VIR_MIGRATE_AUTO_CONVERGE;
+
     if (vshCommandOptBool(cmd, "offline")) {
         flags |= VIR_MIGRATE_OFFLINE;
     }
-- 
1.7.1