rdma: introduce capability x-rdma-pin-all

This capability allows you to disable dynamic chunk registration
for better throughput on high-performance links.

For example, using an 8GB RAM virtual machine with all 8GB of memory in
active use and the VM itself is completely idle using a 40 gbps infiniband link:

1. x-rdma-pin-all disabled total time: approximately 7.5 seconds @ 9.5 Gbps
2. x-rdma-pin-all enabled total time: approximately 4 seconds @ 26 Gbps

These numbers would of course scale up to whatever size virtual machine
you have to migrate using RDMA.

Enabling this feature does *not* have any measurable affect on
migration *downtime*. This is because, without this feature, all of the
memory will have already been registered already in advance during
the bulk round and does not need to be re-registered during the successive
iteration rounds.

Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Chegu Vinod <chegu_vinod@hp.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Tested-by: Chegu Vinod <chegu_vinod@hp.com>
Tested-by: Michael R. Hines <mrhines@us.ibm.com>
Signed-off-by: Michael R. Hines <mrhines@us.ibm.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

diff --git a/include/migration/migration.h b/include/migration/migration.h
index 3ddd64ffcb1f328d53c954abe593e7d59591c820..f0640e0eecb7fb4a0335abc09eff064fcd121d68 100644 (file)
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -123,6 +123,8 @@ void migrate_add_blocker(Error *reason);
  */
 void migrate_del_blocker(Error *reason);
 
+bool migrate_rdma_pin_all(void);
+
 int xbzrle_encode_buffer(uint8_t *old_buf, uint8_t *new_buf, int slen,
                          uint8_t *dst, int dlen);
 int xbzrle_decode_buffer(uint8_t *src, int slen, uint8_t *dst, int dlen);

diff --git a/migration.c b/migration.c
index 441a3b23f948daaf64b0b48323c3c87c674731ed..a704d48669f2bf2d6bcfd941028cdef7f0390814 100644 (file)
--- a/migration.c
+++ b/migration.c
@@ -476,6 +476,15 @@ void qmp_migrate_set_downtime(double value, Error **errp)
     max_downtime = (uint64_t)value;
 }
 
+bool migrate_rdma_pin_all(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->enabled_capabilities[MIGRATION_CAPABILITY_X_RDMA_PIN_ALL];
+}
+
 int migrate_use_xbzrle(void)
 {
     MigrationState *s;

diff --git a/qapi-schema.json b/qapi-schema.json
index 78da5577af90ed1739978998bfc729981281b20b..a30a728dded4626ba957101c8ba896bcbd01d578 100644 (file)
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -608,10 +608,15 @@
 #          This feature allows us to minimize migration traffic for certain work
 #          loads, by sending compressed difference of the pages
 #
+# @x-rdma-pin-all: Controls whether or not the entire VM memory footprint is
+#          mlock()'d on demand or all at once. Refer to docs/rdma.txt for usage.
+#          Disabled by default. Experimental: may (or may not) be renamed after
+#          further testing is complete. (since 1.6)
+#
 # Since: 1.2
 ##
 { 'enum': 'MigrationCapability',
-  'data': ['xbzrle'] }
+  'data': ['xbzrle', 'x-rdma-pin-all'] }
 
 ##
 # @MigrationCapabilityStatus