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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> |
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| .. | ||
| arch_init.c | ||
| balloon.c | ||
| bootdevice.c | ||
| cpu-throttle.c | ||
| cpu-timers.c | ||
| cpus.c | ||
| datadir.c | ||
| device_tree.c | ||
| dma-helpers.c | ||
| globals.c | ||
| icount.c | ||
| ioport.c | ||
| main.c | ||
| memory.c | ||
| memory_mapping.c | ||
| meson.build | ||
| physmem.c | ||
| qdev-monitor.c | ||
| qemu-seccomp.c | ||
| qtest.c | ||
| rtc.c | ||
| runstate-action.c | ||
| runstate.c | ||
| timers-state.h | ||
| tpm.c | ||
| trace-events | ||
| trace.h | ||
| vl.c | ||