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

[Vladimir Sementsov-Ogievskiy]

Thanks for explanation!

07.04.2022 09:42, Hanna Reitz wrote:
> 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).

Hm, I tried but it doesn't help (Add vm.add_args('-accel', 'tcg') before vm.launch() in 
the test), as " -accel qtest" is kept anyway, and therefore 
do_configure_accelerator is called for qtest and finally qtest_allowed is set to true.

But using QEMUMachine class instead of VM helps.

> 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.)

OK, I don't think we need these patches now.

> > 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);


--
Best regards,
Vladimir