10.07.2019, 12:57, "Dr. David Alan Gilbert" <dgilb...@redhat.com>: > * Yury Kotov (yury-ko...@yandex-team.ru) wrote: >> Hi, >> >> I wrote a test for migration auto converge and found out a strange thing: >> 1. Enable auto converge >> 2. Set max-bandwidth 1Gb/s >> 3. Set downtime-limit 1ms >> 4. Run standard test (just writes a byte per page) >> 5. Wait for converge >> 6. It's converged with 99% throttle percentage >> 7. The result downtime was about 300-600ms <<<< >> >> It's much higher than expected 1ms. I figured out that cpu_throttle_thread() >> function sleeps for 100ms+ for high throttle percentage (>=95%) in VCPU >> thread. >> And it sleeps even after a cpu kick. >> >> I tried to fix it by using timedwait for ms part of sleep. >> E.g timedwait(halt_cond, 1ms) + usleep(500). >> >> But I'm not sure about using timedwait function here with qemu_global_mutex. >> The original function uses qemu_mutex_unlock_iothread + >> qemu_mutex_lock_iothread >> It differs from locking/unlocking (inside timedwait) qemu_global_mutex >> because of using qemu_bql_mutex_lock_func function which could be anything. >> This is why the series is RFC. >> >> What do you think? > > Would qemu_sem_timedwait work for your use? I use it in > migration_thread for the bandwidth limiting and allowing that to be > woken up.
It's a good idea and it should work. But it's more complicated than reusing halt_cond. I see that it's ok to use qemu_cond_wait in cpus.c so I hope it's ok to use qemu_cond_timedwait too. But if it isn't then using qemu_sem_timedwait is a good fallback I think. Regards, Yury > > Dave > >> Thanks! >> >> Yury Kotov (2): >> qemu-thread: Add qemu_cond_timedwait >> cpus: Fix throttling during vm_stop >> >> cpus.c | 27 +++++++++++++++++++-------- >> include/qemu/thread.h | 12 ++++++++++++ >> util/qemu-thread-posix.c | 40 ++++++++++++++++++++++++++++------------ >> util/qemu-thread-win32.c | 16 ++++++++++++++++ >> 4 files changed, 75 insertions(+), 20 deletions(-) >> >> -- >> 2.22.0 > -- > Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
