diff options
authorUtkarsh Tripathi <utkarsh.tripathi@nutanix.com>2020-12-31 13:13:04 +0000
committerPaolo Bonzini <pbonzini@redhat.com>2021-02-08 15:15:32 +0100
commit33c38f8ca1e09b9f77cf263404d423e076c19177 (patch)
parent54550d886e5bb4148c0765c639fa04a44f3e5d8d (diff)
cpu-throttle: Remove timer_mod() from cpu_throttle_set()
During migrations, after each iteration, cpu_throttle_set() is called, which irrespective of input, re-arms the timer according to value of new_throttle_pct. This causes cpu_throttle_thread() to be delayed in getting scheduled and consqeuntly lets guest run for more time than what the throttle value should allow. This leads to spikes in guest throughput at high cpu-throttle percentage whenever cpu_throttle_set() is called. A solution would be not to modify the timer immediately in cpu_throttle_set(), instead, only modify throttle_percentage so that the throttle would automatically adjust to the required percentage when cpu_throttle_timer_tick() is invoked. Manually tested the patch using following configuration: Guest: Centos7 (3.10.0-123.el7.x86_64) Total Memory - 64GB , CPUs - 16 Tool used - stress (1.0.4) Workload - stress --vm 32 --vm-bytes 1G --vm-keep Migration Parameters: Network Bandwidth - 500MBPS cpu-throttle-initial - 99 Results: With timer_mod(): fails to converge, continues indefinitely Without timer_mod(): converges in 249 sec Signed-off-by: Utkarsh Tripathi <utkarsh.tripathi@nutanix.com> Message-Id: <1609420384-119407-1-git-send-email-utkarsh.tripathi@nutanix.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
1 files changed, 9 insertions, 2 deletions
diff --git a/softmmu/cpu-throttle.c b/softmmu/cpu-throttle.c
index 2ec4b8e0bc..8c2144ab95 100644
--- a/softmmu/cpu-throttle.c
+++ b/softmmu/cpu-throttle.c
@@ -90,14 +90,21 @@ static void cpu_throttle_timer_tick(void *opaque)
void cpu_throttle_set(int new_throttle_pct)
+ /*
+ * boolean to store whether throttle is already active or not,
+ * before modifying throttle_percentage
+ */
+ bool throttle_active = cpu_throttle_active();
/* Ensure throttle percentage is within valid range */
new_throttle_pct = MIN(new_throttle_pct, CPU_THROTTLE_PCT_MAX);
new_throttle_pct = MAX(new_throttle_pct, CPU_THROTTLE_PCT_MIN);
qatomic_set(&throttle_percentage, new_throttle_pct);
- timer_mod(throttle_timer, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL_RT) +
+ if (!throttle_active) {
+ cpu_throttle_timer_tick(NULL);
+ }
void cpu_throttle_stop(void)