Re: [PATCH 1/2] block/throttle-groups: use QEMU_CLOCK_REALTIME for qtest too

[Hanna Reitz]

On 06.04.22 17:32, Vladimir Sementsov-Ogievskiy wrote:
> Virtual clock just doesn't tick for iotests, and throttling just not
> work. Let's use realtime clock.

It does tick when you make it take, specifically with the clock_step 
qtest command.  093 does this, and so with this patch, it fails, because 
it is no longer deterministic.

So far, if I needed realtime throttling, I simply switched the 
accelerator to tcg (e.g. in stream-error-on-reset).

I’m not really opposed to this, but it does break 093, and without 
looking too closely into it, I would guess that it’d be difficult to 
rewrite 093 in a deterministic way without it relying on throttling 
using the virtual clock.  (A runtime option for the throttle-group 
object to choose the clock type might be an option.)

> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@openvz.org>
> ---
>   block/throttle-groups.c | 4 ----
>   1 file changed, 4 deletions(-)
>
> diff --git a/block/throttle-groups.c b/block/throttle-groups.c
> index fb203c3ced..029158d797 100644
> --- a/block/throttle-groups.c
> +++ b/block/throttle-groups.c
> @@ -753,10 +753,6 @@ static void throttle_group_obj_init(Object *obj)
>       ThrottleGroup *tg = THROTTLE_GROUP(obj);
>   
>       tg->clock_type = QEMU_CLOCK_REALTIME;
> -    if (qtest_enabled()) {
> -        /* For testing block IO throttling only */
> -        tg->clock_type = QEMU_CLOCK_VIRTUAL;
> -    }
>       tg->is_initialized = false;
>       qemu_mutex_init(&tg->lock);
>       throttle_init(&tg->ts);