Re: [Qemu-devel] [PATCH 07/18] throttle-groups: only start one coroutine from drained_begin

[Stefan Hajnoczi]

On Thu, May 11, 2017 at 04:41:57PM +0200, Paolo Bonzini wrote:
> Starting all waiting coroutines from bdrv_drain_all is unnecessary;
> throttle_group_co_io_limits_intercept calls schedule_next_request as
> soon as the coroutine restarts, which in turn will restart the next
> request if possible.
> 
> If we only start the first request and let the coroutines dance from
> there the code is simpler and there is more reuse between
> throttle_group_config, throttle_group_restart_blk and timer_cb.  The
> next patch will benefit from this.
> 
> We also stop accessing from throttle_group_restart_blk the
> blkp->throttled_reqs CoQueues even when there was no
> attached throttling group.  This worked but is not pretty.
> 
> The only thing that can interrupt the dance is the QEMU_CLOCK_VIRTUAL
> timer when switching from one block device to the next, because the
> timer is set to "now + 1" but QEMU_CLOCK_VIRTUAL might not be running.
> Set that timer to point in the present ("now") rather than the future
> and things work.
> 
> Signed-off-by: Paolo Bonzini <address@hidden>
> ---
>         v1->v2: new
> 
>  block/throttle-groups.c | 45 +++++++++++++++++++++++++--------------------
>  1 file changed, 25 insertions(+), 20 deletions(-)

Reviewed-by: Stefan Hajnoczi <address@hidden>

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