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Re: [Qemu-devel] [PATCH v4 0/3] High downtime with 95+ throttle pct


From: Yury Kotov
Subject: Re: [Qemu-devel] [PATCH v4 0/3] High downtime with 95+ throttle pct
Date: Wed, 07 Aug 2019 10:42:06 +0300

Ping

23.07.2019, 16:42, "Yury Kotov" <address@hidden>:
> Hi,
>
> V4:
> * The test was simplified to prevent false fails.
>
> V3:
> * Rebase fixes (migrate_set_parameter -> migrate_set_parameter_int)
>
> V2:
> * Added a test
> * Fixed qemu_cond_timedwait for qsp
>
> 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.
>
> Fixed it by using timedwait for ms part of sleep.
> E.g timedwait(halt_cond, 1ms) + usleep(500).
>
> Regards,
> Yury
>
> Yury Kotov (3):
>   qemu-thread: Add qemu_cond_timedwait
>   cpus: Fix throttling during vm_stop
>   tests/migration: Add a test for auto converge
>
>  cpus.c | 27 +++++++---
>  include/qemu/thread.h | 18 +++++++
>  tests/migration-test.c | 103 ++++++++++++++++++++++++++++++++++-----
>  util/qemu-thread-posix.c | 40 ++++++++++-----
>  util/qemu-thread-win32.c | 16 ++++++
>  util/qsp.c | 18 +++++++
>  6 files changed, 191 insertions(+), 31 deletions(-)
>
> --
> 2.22.0



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