migration/migration-hmp-cmds.c | 11 +++++++++++ migration/options.c | 33 ++++++++++++++++++++++++++++++++- migration/options.h | 1 + migration/rdma.c | 30 ++++++++++++++++-------------- qapi/migration.json | 12 ++++++++++-- 5 files changed, 70 insertions(+), 17 deletions(-)
The default 1MB RDMA chunk size causes slow live migration because
each chunk triggers a write_flush (ibv_post_send). For 8GB RAM,
1MB chunk size produces ~15000 flushes vs ~3700 with 1024MB chunk size.
Add x-rdma-chunk-size parameter to configure the RDMA chunk size for
faster migration.
Usage: `migrate_set_parameter x-rdma-chunk-size 1024M`
Performance with RDMA live migration of 8GB RAM VM:
| x-rdma-chunk-size (B) | time (s) | throughput (MB/s) |
|-----------------------|----------|-------------------|
| 1M (default) | 37.915 | 1,007 |
| 32M | 17.880 | 2,260 |
| 1024M | 4.368 | 17,529 |
Signed-off-by: Samuel Zhang <guoqing.zhang@amd.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
---
v2:
- Renamed x-rdma-chunk-shift to x-rdma-chunk-size (byte count)
- Added validation in migrate_params_check()
- Added hmp_migrate_set_parameter() support
- Added hmp_info_migrate_parameters() support
- Added migrate_mark_all_params_present()
- Use qemu_strtosz() for size suffix support
v3: [Markus]
- Use visit_type_size() in HMP set parameter
- Use MiB/GiB constants
v4: [Markus]
- Remove superfluous comment on DEFAULT_MIGRATE_X_RDMA_CHUNK_SIZE
- Use "Only applies when migrating via RDMA" in QAPI doc
migration/migration-hmp-cmds.c | 11 +++++++++++
migration/options.c | 33 ++++++++++++++++++++++++++++++++-
migration/options.h | 1 +
migration/rdma.c | 30 ++++++++++++++++--------------
qapi/migration.json | 12 ++++++++++--
5 files changed, 70 insertions(+), 17 deletions(-)
diff --git a/migration/migration-hmp-cmds.c b/migration/migration-hmp-cmds.c
index 0a193b8f54..4f6c1dbf89 100644
--- a/migration/migration-hmp-cmds.c
+++ b/migration/migration-hmp-cmds.c
@@ -451,6 +451,13 @@ void hmp_info_migrate_parameters(Monitor *mon, const QDict *qdict)
params->direct_io ? "on" : "off");
}
+ if (params->has_x_rdma_chunk_size) {
+ monitor_printf(mon, "%s: %" PRIu64 " bytes\n",
+ MigrationParameter_str(
+ MIGRATION_PARAMETER_X_RDMA_CHUNK_SIZE),
+ params->x_rdma_chunk_size);
+ }
+
assert(params->has_cpr_exec_command);
monitor_print_cpr_exec_command(mon, params->cpr_exec_command);
}
@@ -734,6 +741,10 @@ void hmp_migrate_set_parameter(Monitor *mon, const QDict *qdict)
p->has_direct_io = true;
visit_type_bool(v, param, &p->direct_io, &err);
break;
+ case MIGRATION_PARAMETER_X_RDMA_CHUNK_SIZE:
+ p->has_x_rdma_chunk_size = true;
+ visit_type_size(v, param, &p->x_rdma_chunk_size, &err);
+ break;
case MIGRATION_PARAMETER_CPR_EXEC_COMMAND: {
/*
* NOTE: g_autofree will only auto g_free() the strv array when
diff --git a/migration/options.c b/migration/options.c
index f33b297929..b3565235d7 100644
--- a/migration/options.c
+++ b/migration/options.c
@@ -13,6 +13,7 @@
#include "qemu/osdep.h"
#include "qemu/error-report.h"
+#include "qemu/units.h"
#include "exec/target_page.h"
#include "qapi/clone-visitor.h"
#include "qapi/error.h"
@@ -90,6 +91,7 @@ const PropertyInfo qdev_prop_StrOrNull;
#define DEFAULT_MIGRATE_VCPU_DIRTY_LIMIT_PERIOD 1000 /* milliseconds */
#define DEFAULT_MIGRATE_VCPU_DIRTY_LIMIT 1 /* MB/s */
+#define DEFAULT_MIGRATE_X_RDMA_CHUNK_SIZE MiB
const Property migration_properties[] = {
DEFINE_PROP_BOOL("store-global-state", MigrationState,
@@ -183,6 +185,9 @@ const Property migration_properties[] = {
DEFINE_PROP_ZERO_PAGE_DETECTION("zero-page-detection", MigrationState,
parameters.zero_page_detection,
ZERO_PAGE_DETECTION_MULTIFD),
+ DEFINE_PROP_UINT64("x-rdma-chunk-size", MigrationState,
+ parameters.x_rdma_chunk_size,
+ DEFAULT_MIGRATE_X_RDMA_CHUNK_SIZE),
/* Migration capabilities */
DEFINE_PROP_MIG_CAP("x-xbzrle", MIGRATION_CAPABILITY_XBZRLE),
@@ -993,6 +998,15 @@ ZeroPageDetection migrate_zero_page_detection(void)
return s->parameters.zero_page_detection;
}
+uint64_t migrate_rdma_chunk_size(void)
+{
+ MigrationState *s = migrate_get_current();
+ uint64_t size = s->parameters.x_rdma_chunk_size;
+
+ assert(MiB <= size && size <= GiB && is_power_of_2(size));
+ return size;
+}
+
/* parameters helpers */
AnnounceParameters *migrate_announce_params(void)
@@ -1055,7 +1069,7 @@ static void migrate_mark_all_params_present(MigrationParameters *p)
&p->has_announce_step, &p->has_block_bitmap_mapping,
&p->has_x_vcpu_dirty_limit_period, &p->has_vcpu_dirty_limit,
&p->has_mode, &p->has_zero_page_detection, &p->has_direct_io,
- &p->has_cpr_exec_command,
+ &p->has_x_rdma_chunk_size, &p->has_cpr_exec_command,
};
len = ARRAY_SIZE(has_fields);
@@ -1266,6 +1280,15 @@ bool migrate_params_check(MigrationParameters *params, Error **errp)
return false;
}
+ if (params->has_x_rdma_chunk_size &&
+ (params->x_rdma_chunk_size < MiB ||
+ params->x_rdma_chunk_size > GiB ||
+ !is_power_of_2(params->x_rdma_chunk_size))) {
+ error_setg(errp, "Option x_rdma_chunk_size expects "
+ "a power of 2 in the range 1MiB to 1024MiB");
+ return false;
+ }
+
return true;
}
@@ -1391,6 +1414,10 @@ static void migrate_params_test_apply(MigrationParameters *params,
dest->direct_io = params->direct_io;
}
+ if (params->has_x_rdma_chunk_size) {
+ dest->x_rdma_chunk_size = params->x_rdma_chunk_size;
+ }
+
if (params->has_cpr_exec_command) {
dest->cpr_exec_command = params->cpr_exec_command;
}
@@ -1517,6 +1544,10 @@ static void migrate_params_apply(MigrationParameters *params)
s->parameters.direct_io = params->direct_io;
}
+ if (params->has_x_rdma_chunk_size) {
+ s->parameters.x_rdma_chunk_size = params->x_rdma_chunk_size;
+ }
+
if (params->has_cpr_exec_command) {
qapi_free_strList(s->parameters.cpr_exec_command);
s->parameters.cpr_exec_command =
diff --git a/migration/options.h b/migration/options.h
index b502871097..b46221998a 100644
--- a/migration/options.h
+++ b/migration/options.h
@@ -87,6 +87,7 @@ const char *migrate_tls_creds(void);
const char *migrate_tls_hostname(void);
uint64_t migrate_xbzrle_cache_size(void);
ZeroPageDetection migrate_zero_page_detection(void);
+uint64_t migrate_rdma_chunk_size(void);
/* parameters helpers */
diff --git a/migration/rdma.c b/migration/rdma.c
index 55ab85650a..3e37a1d440 100644
--- a/migration/rdma.c
+++ b/migration/rdma.c
@@ -45,10 +45,12 @@
#define RDMA_RESOLVE_TIMEOUT_MS 10000
/* Do not merge data if larger than this. */
-#define RDMA_MERGE_MAX (2 * 1024 * 1024)
-#define RDMA_SIGNALED_SEND_MAX (RDMA_MERGE_MAX / 4096)
+static inline uint64_t rdma_merge_max(void)
+{
+ return migrate_rdma_chunk_size() * 2;
+}
-#define RDMA_REG_CHUNK_SHIFT 20 /* 1 MB */
+#define RDMA_SIGNALED_SEND_MAX 512
/*
* This is only for non-live state being migrated.
@@ -527,21 +529,21 @@ static int qemu_rdma_exchange_send(RDMAContext *rdma, RDMAControlHeader *head,
static inline uint64_t ram_chunk_index(const uint8_t *start,
const uint8_t *host)
{
- return ((uintptr_t) host - (uintptr_t) start) >> RDMA_REG_CHUNK_SHIFT;
+ return ((uintptr_t) host - (uintptr_t) start) / migrate_rdma_chunk_size();
}
static inline uint8_t *ram_chunk_start(const RDMALocalBlock *rdma_ram_block,
uint64_t i)
{
return (uint8_t *)(uintptr_t)(rdma_ram_block->local_host_addr +
- (i << RDMA_REG_CHUNK_SHIFT));
+ (i * migrate_rdma_chunk_size()));
}
static inline uint8_t *ram_chunk_end(const RDMALocalBlock *rdma_ram_block,
uint64_t i)
{
uint8_t *result = ram_chunk_start(rdma_ram_block, i) +
- (1UL << RDMA_REG_CHUNK_SHIFT);
+ migrate_rdma_chunk_size();
if (result > (rdma_ram_block->local_host_addr + rdma_ram_block->length)) {
result = rdma_ram_block->local_host_addr + rdma_ram_block->length;
@@ -1841,6 +1843,7 @@ static int qemu_rdma_write_one(RDMAContext *rdma,
struct ibv_send_wr *bad_wr;
int reg_result_idx, ret, count = 0;
uint64_t chunk, chunks;
+ uint64_t chunk_size = migrate_rdma_chunk_size();
uint8_t *chunk_start, *chunk_end;
RDMALocalBlock *block = &(rdma->local_ram_blocks.block[current_index]);
RDMARegister reg;
@@ -1861,22 +1864,21 @@ retry:
chunk_start = ram_chunk_start(block, chunk);
if (block->is_ram_block) {
- chunks = length / (1UL << RDMA_REG_CHUNK_SHIFT);
+ chunks = length / chunk_size;
- if (chunks && ((length % (1UL << RDMA_REG_CHUNK_SHIFT)) == 0)) {
+ if (chunks && ((length % chunk_size) == 0)) {
chunks--;
}
} else {
- chunks = block->length / (1UL << RDMA_REG_CHUNK_SHIFT);
+ chunks = block->length / chunk_size;
- if (chunks && ((block->length % (1UL << RDMA_REG_CHUNK_SHIFT)) == 0)) {
+ if (chunks && ((block->length % chunk_size) == 0)) {
chunks--;
}
}
trace_qemu_rdma_write_one_top(chunks + 1,
- (chunks + 1) *
- (1UL << RDMA_REG_CHUNK_SHIFT) / 1024 / 1024);
+ (chunks + 1) * chunk_size / 1024 / 1024);
chunk_end = ram_chunk_end(block, chunk + chunks);
@@ -2176,7 +2178,7 @@ static int qemu_rdma_write(RDMAContext *rdma,
rdma->current_length += len;
/* flush it if buffer is too large */
- if (rdma->current_length >= RDMA_MERGE_MAX) {
+ if (rdma->current_length >= rdma_merge_max()) {
return qemu_rdma_write_flush(rdma, errp);
}
@@ -3522,7 +3524,7 @@ int rdma_registration_handle(QEMUFile *f)
} else {
chunk = reg->key.chunk;
host_addr = block->local_host_addr +
- (reg->key.chunk * (1UL << RDMA_REG_CHUNK_SHIFT));
+ (reg->key.chunk * migrate_rdma_chunk_size());
/* Check for particularly bad chunk value */
if (host_addr < (void *)block->local_host_addr) {
error_report("rdma: bad chunk for block %s"
diff --git a/qapi/migration.json b/qapi/migration.json
index 7134d4ce47..f78a20f65a 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -806,7 +806,7 @@
#
# Features:
#
-# @unstable: Members @x-checkpoint-delay and
+# @unstable: Members @x-checkpoint-delay, @x-rdma-chunk-size, and
# @x-vcpu-dirty-limit-period are experimental.
#
# Since: 2.4
@@ -831,6 +831,7 @@
'mode',
'zero-page-detection',
'direct-io',
+ { 'name': 'x-rdma-chunk-size', 'features': [ 'unstable' ] },
'cpr-exec-command'] }
##
@@ -1007,9 +1008,14 @@
# is @cpr-exec. The first list element is the program's filename,
# the remainder its arguments. (Since 10.2)
#
+# @x-rdma-chunk-size: RDMA memory registration chunk size in bytes.
+# Default is 1MiB. Must be a power of 2 in the range
+# [1MiB, 1024MiB]. Only applies when migrating via RDMA.
+# (Since 11.1)
+#
# Features:
#
-# @unstable: Members @x-checkpoint-delay and
+# @unstable: Members @x-checkpoint-delay, @x-rdma-chunk-size, and
# @x-vcpu-dirty-limit-period are experimental.
#
# Since: 2.4
@@ -1046,6 +1052,8 @@
'*mode': 'MigMode',
'*zero-page-detection': 'ZeroPageDetection',
'*direct-io': 'bool',
+ '*x-rdma-chunk-size': { 'type': 'uint64',
+ 'features': [ 'unstable' ] },
'*cpr-exec-command': [ 'str' ]} }
##
--
2.43.7© 2016 - 2026 Red Hat, Inc.