migrate/cpu-throttle: Add max-cpu-throttle migration parameter

Currently, the default maximum CPU throttle for migration is
99(CPU_THROTTLE_PCT_MAX). This is too big and can make a remarkable
performance effect for the guest. We see a lot of packets latency
exceed 500ms when the CPU_THROTTLE_PCT_MAX reached. This patch set
adds a new max-cpu-throttle parameter to limit the CPU throttle.

Signed-off-by: Li Qiang <liq3ea@gmail.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/migration/ram.c b/migration/ram.c
index fa79d0a5b9..1e5c45a514 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1391,13 +1391,15 @@ static void mig_throttle_guest_down(void)
     MigrationState *s = migrate_get_current();
     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;
 
     /* We have not started throttling yet. Let's start it. */
     if (!cpu_throttle_active()) {
         cpu_throttle_set(pct_initial);
     } else {
         /* Throttling already on, just increase the rate */
-        cpu_throttle_set(cpu_throttle_get_percentage() + pct_icrement);
+        cpu_throttle_set(MIN(cpu_throttle_get_percentage() + pct_icrement,
+                         pct_max));
     }
 }