| Message ID | 20190710092338.23559-1-yury-kotov@yandex-team.ru (mailing list archive) |
|---|---|
| Headers | show |
| Series | High downtime with 95+ throttle pct | expand |
* Yury Kotov (yury-kotov@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. 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 / dgilbert@redhat.com / Manchester, UK
10.07.2019, 12:57, "Dr. David Alan Gilbert" <dgilbert@redhat.com>: > * Yury Kotov (yury-kotov@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 / dgilbert@redhat.com / Manchester, UK