The current autoconverge algorithm does not obtain the threshold
that currently requires the CPU to limit the speed through
calculation, but limits the speed of the CPU through continuous
attempts. Start from an initial value to limit the speed. If the
migration can not be completed for two consecutive rounds, increase
the limit threshold and continue to try until the limit threshold
reaches 99%. If the memory pressure is high or the migration
bandwidth is low, then it will gradually increase from the initial
20% to 99%, which will be a long and time-consuming process.
This optimization method calculates a matching rate limit
threshold according to the current migration bandwidth and the
rate of current dirty page generation. When the memory pressure
is high, this optimization can reduce the unnecessary and
time-consuming process of constantly trying to increase the
limit, and significantly improve the efficiency of migration.
Test results after optimization(VM 8C32G, qemu stress tool):
mem_stress caculated_auto_converge_throttle bandwidth(MiB/s)
300M 0 1000M
400M 0 1000M
1G 50 1000M
2G 80 1000M
3G 90 1000M
4G 90 1000M
5G 90 1000M
6G 99 1000M
10G 99 1000M
20G 99 1000M
30G 99 1000M
Series optimization summary:
Related Patch Series:
[1]kvm,memory: Optimize dirty page collection for dirty ring
[2]kvm: Dynamically control the load of the reaper thread
[3]kvm: Dirty ring autoconverge optmization for kvm_cpu_
synchronize_kick_all
[4]kvm: Introduce a dirty rate calculation method based on dirty
ring
[5]migration: Calculate the appropriate throttle for autoconverge
Test environment:
Host: 64 cpus(Intel(R) Xeon(R) Gold 5218 CPU @ 2.30GHz),
512G memory,
10G NIC
VM: 2 cpus,4G memory and 8 cpus, 32G memory
memory stress: run stress(qemu) in VM to generates memory stress
Test1: Massive online migration(Run each test item 50 to 200 times)
Test command: virsh -t migrate $vm --live --p2p --unsafe
--undefinesource --persistent --auto-converge --migrateuri
tcp://${data_ip_remote}
*********** Use optimized dirtry ring ***********
ring_size mem_stress VM average_migration_time(ms)
4096 1G 2C4G 15888
4096 3G 2C4G 13320
65536 1G 2C4G 10036
65536 3G 2C4G 12132
4096 4G 8C32G 53629
4096 8G 8C32G 62474
4096 30G 8C32G 99025
65536 4G 8C32G 45563
65536 8G 8C32G 61114
65536 30G 8C32G 102087
*********** Use Unoptimized dirtry ring ***********
ring_size mem_stress VM average_migration_time(ms)
4096 1G 2C4G 23992
4096 3G 2C4G 44234
65536 1G 2C4G 24546
65536 3G 2C4G 44939
4096 4G 8C32G 88441
4096 8G 8C32G may not complete
4096 30G 8C32G 602884
65536 4G 8C32G 335535
65536 8G 8C32G 1249232
65536 30G 8C32G 616939
*********** Use bitmap dirty tracking ***********
ring_size mem_stress VM average_migration_time(ms)
0 1G 2C4G 24597
0 3G 2C4G 45254
0 4G 8C32G 103773
0 8G 8C32G 129626
0 30G 8C32G 588212
Compared with the old bitmap method and the unoptimized dirty ring,
the migration time of the optimized dirty ring from the sorted data
is greatly improved, especially when the virtual machine memory is
large and the memory pressure is high, the effect is more obvious,
can achieve five to six times the migration acceleration effect.
And during the test, it was found that the dirty ring could not be
completed for a long time after adding certain memory pressure.
The optimized dirty ring did not encounter such a problem.
Test2: qemu guestperf test
Test ommand parameters: --auto-converge --stress-mem XX
--downtime 300 --bandwidth 10000
*********** Use optimized dirtry ring ***********
ring_size stress VM Significant_perf max_memory_update cost_time(s)
_drop_duration(s) speed(ms/GB)
4096 3G 2C4G 5.5 2962 23.5
65536 3G 2C4G 6 3160 25
4096 3G 8C32G 13 7921 38
4096 6G 8C32G 16 11.6K 46
4096 10G 8C32G 12.1 11.2K 47.6
4096 20G 8C32G 20 20.2K 71
4096 30G 8C32G 29.5 29K 94.5
65536 3G 8C32G 14 8700 40
65536 6G 8C32G 15 12K 46
65536 10G 8C32G 11.5 11.1k 47.5
65536 20G 8C32G 21 20.9K 72
65536 30G 8C32G 29.5 29.1K 94.5
*********** Use Unoptimized dirtry ring ***********
ring_size stress VM Significant_perf max_memory_update cost_time(s)
_drop_duration(s) speed(ms/GB)
4096 3G 2C4G 23 2766 46
65536 3G 2C4G 22.2 3283 46
4096 3G 8C32G 62 48.8K 106
4096 6G 8C32G 68 23.87K 124
4096 10G 8C32G 91 16.87K 190
4096 20G 8C32G 152.8 28.65K 336.8
4096 30G 8C32G 187 41.19K 502
65536 3G 8C32G 71 12.7K 67
65536 6G 8C32G 63 12K 46
65536 10G 8C32G 88 25.3k 120
65536 20G 8C32G 157.3 25K 391
65536 30G 8C32G 171 30.8K 487
*********** Use bitmap dirty tracking ***********
ring_size stress VM Significant_perf max_memory_update cost_time(s)
_drop_duration(s) speed(ms/GB)
0 3G 2C4G 18 3300 38
0 3G 8C32G 38 7571 66
0 6G 8C32G 61.5 10.5K 115.5
0 10G 8C32G 110 13.68k 180
0 20G 8C32G 161.6 24.4K 280
0 30G 8C32G 221.5 28.4K 337.5
The above test data shows that the guestperf performance of the
optimized dirty ring during the migration process is significantly
better than that of the unoptimized dirty ring, and slightly better
than the bitmap method.
During the migration process of the optimized dirty ring, the migration
time is greatly reduced, and the time in the period of significant
memory performance degradation is significantly shorter than that of
the bitmap mode and the unoptimized dirty ring mode. Therefore, the
optimized ditry ring can better reduce the impact on guests accessing
memory resources during the migration process.
Signed-off-by: Chongyun Wu <wucy11@xxxxxxxxxxxxxxx>
---
accel/kvm/kvm-all.c | 7 ++++--
migration/migration.c | 1 +
migration/migration.h | 2 ++
migration/ram.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++++---
4 files changed, 69 insertions(+), 5 deletions(-)
diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index 05af6ce..87c2c6a 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -798,7 +798,11 @@ int64_t kvm_dirty_ring_get_rate(void)
int64_t kvm_dirty_ring_get_peak_rate(void)
{
- return kvm_state->reaper.counter.dirty_pages_period_peak_rate;
+ int64_t rate = kvm_state->reaper.counter.dirty_pages_period_peak_rate;
+ /* Reset the peak rate to calculate a new peak rate after this moment */
+ kvm_state->reaper.counter.dirty_pages_period_peak_rate = 0;
+
+ return rate;
}
static void kvm_dirty_ring_reap_count(KVMState *s)
@@ -834,7 +838,6 @@ static void kvm_dirty_ring_reap_count(KVMState *s)
s->reaper.counter.dirty_pages_period_peak_rate =
s->reaper.counter.dirty_pages_rate;
}
-
/* Reset counters */
s->reaper.counter.dirty_pages_period = 0;
s->reaper.counter.time_last_count = 0;
diff --git a/migration/migration.c b/migration/migration.c
index 1114b2f..13a8c1c 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -2065,6 +2065,7 @@ void migrate_init(MigrationState *s)
s->vm_was_running = false;
s->iteration_initial_bytes = 0;
s->threshold_size = 0;
+ s->have_caculated_throttle_pct = false;
}
int migrate_add_blocker_internal(Error *reason, Error **errp)
diff --git a/migration/migration.h b/migration/migration.h
index 8130b70..fe50439 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -296,6 +296,8 @@ struct MigrationState {
* This save hostname when out-going migration starts
*/
char *hostname;
+ /* If already caculated the throttle percentage for migration */
+ bool have_caculated_throttle_pct;
};
void migrate_set_state(int *state, int old_state, int new_state);
diff --git a/migration/ram.c b/migration/ram.c
index 91ca743..7f08a34 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -62,6 +62,7 @@
#include "qemu/userfaultfd.h"
#endif /* defined(__linux__) */
+#include "sysemu/kvm.h"
/***********************************************************/
/* ram save/restore */
@@ -616,6 +617,64 @@ static size_t save_page_header(RAMState *rs, QEMUFile *f,
RAMBlock *block,
}
/**
+ * Calculate the matched speed limit threshold according to
+ * the current migration bandwidth and the current rate of
+ * dirty pages to aviod time-consuming and pointless attempt.
+ */
+static int calculate_throttle_pct(void)
+{
+ MigrationState *s = migrate_get_current();
+ uint64_t threshold = s->parameters.throttle_trigger_threshold;
+ uint64_t pct_initial = s->parameters.cpu_throttle_initial;
+ uint64_t pct_icrement = s->parameters.cpu_throttle_increment;
+ int pct_max = s->parameters.max_cpu_throttle;
+
+ int matched_pct = 0;
+ float facter1 = 0.0;
+ float facter2 = 0.0;
+ int64_t dirty_pages_rate = 0;
+ double bandwith_expect = 0.0;
+ double dirty_pages_rate_expect = 0.0;
+ double bandwith = (s->mbps / 8) * 1024 * 1024;
+
+ if (kvm_dirty_ring_enabled()) {
+ dirty_pages_rate = kvm_dirty_ring_get_peak_rate() *
+ qemu_target_page_size();
+ } else {
+ dirty_pages_rate = ram_counters.dirty_pages_rate *
+ qemu_target_page_size();
+ }
+
+ if (dirty_pages_rate) {
+ facter1 = (float)threshold / 100;
+ bandwith_expect = bandwith * facter1;
+
+ for (uint64_t i = pct_initial; i <= pct_max;) {
+ facter2 = 1 - (float)i / 100;
+ dirty_pages_rate_expect = dirty_pages_rate * facter2;
+
+ if (bandwith_expect > dirty_pages_rate_expect) {
+ matched_pct = i;
+ break;
+ }
+ i += pct_icrement;
+ }
+
+ if (!matched_pct) {
+ info_report("Not find matched throttle pct, "
+ "maybe pressure too high, use max");
+ matched_pct = pct_max;
+ }
+ } else {
+ matched_pct = pct_initial;
+ }
+
+ s->have_caculated_throttle_pct = true;
+
+ return matched_pct;
+}
+
+/**
* mig_throttle_guest_down: throttle down the guest
*
* Reduce amount of guest cpu execution to hopefully slow down memory
@@ -628,7 +687,6 @@ static void mig_throttle_guest_down(uint64_t bytes_dirty_period,
uint64_t bytes_dirty_threshold)
{
MigrationState *s = migrate_get_current();
- uint64_t pct_initial = s->parameters.cpu_throttle_initial;
uint64_t pct_increment = s->parameters.cpu_throttle_increment;
bool pct_tailslow = s->parameters.cpu_throttle_tailslow;
int pct_max = s->parameters.max_cpu_throttle;
@@ -637,8 +695,8 @@ static void mig_throttle_guest_down(uint64_t bytes_dirty_period,
uint64_t cpu_now, cpu_ideal, throttle_inc;
/* We have not started throttling yet. Let's start it. */
- if (!cpu_throttle_active()) {
- cpu_throttle_set(pct_initial);
+ if (!s->have_caculated_throttle_pct) {
+ cpu_throttle_set(MIN(calculate_throttle_pct(), pct_max));
} else {
/* Throttling already on, just increase the rate */
if (!pct_tailslow) {
--
1.8.3.1
--
Best Regard,
Chongyun Wu
