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Re: [Qemu-devel] [PATCH 0/3] throttle: use AioContext for dataplane supp
Re: [Qemu-devel] [PATCH 0/3] throttle: use AioContext for dataplane support
Wed, 14 May 2014 17:14:52 +0200
The Wednesday 14 May 2014 à 16:22:44 (+0200), Stefan Hajnoczi wrote :
> This series applies on top of my "dataplane: use QEMU block layer" series.
> Now that the dataplane code path is using the QEMU block layer we should make
> I/O throttling limits safe to use. When the block_set_io_throttle monitor
> command is executed, the BlockDriverState's AioContext must be acquired in
> order to prevent race conditions with the IOThread that is processing requests
> from the guest.
> The new block layer AioContext detach/attach mechanism needs to be extended to
> move the throttling timer to a new AioContext. This makes throttling work
> across bdrv_set_aio_context() calls.
> The result of this series is that I/O throttling works with dataplane and
> limits may be changed at runtime using the monitor.
> Stefan Hajnoczi (3):
> throttle: add throttle_detach/attach_aio_context()
> throttle: add detach/attach test case
> blockdev: acquire AioContext in block_set_io_throttle
> block.c | 7 +++++++
> blockdev.c | 6 ++++++
> include/qemu/throttle.h | 10 ++++++++++
> tests/test-throttle.c | 49
> util/throttle.c | 27 +++++++++++++++++++++++----
> 5 files changed, 90 insertions(+), 9 deletions(-)
As a side note the throttling code does eat some CPU time.
So if people starts using throttling with dataplane by setting 50k iops as a
the timers callback will start to kill half a core.
The solution could be to optionaly make the throttling resolution coarser.
I have future plan to do this for SSD usage