Re: [PATCH 07/18] drm/i915: Combine tasklet_kill and tasklet_disable

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Chris Wilson <chris@chris-wilson.co.uk> writes:

> Quoting Mika Kuoppala (2018-04-24 13:26:11)
>> Chris Wilson <chris@chris-wilson.co.uk> writes:
>> 
>> > Ideally, we want to atomically flush and disable the tasklet before
>> > resetting the GPU. At present, we rely on being the only part to touch
>> > our tasklet and serialisation of the reset process to ensure that we can
>> > suspend the tasklet from the mix of reset/wedge pathways. In this patch,
>> > we move the tasklet abuse into its own function and tweak it such that
>> > we only do a synchronous operation the first time it is disabled around
>> > the reset. This allows us to avoid the sync inside a softirq context in
>> > subsequent patches.
>> >
>> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
>> > Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
>> > Cc: Michał Winiarski <michal.winiarski@intel.com>
>> > CC: Michel Thierry <michel.thierry@intel.com>
>> > Cc: Jeff McGee <jeff.mcgee@intel.com>
>> > ---
>> >  drivers/gpu/drm/i915/intel_lrc.c | 14 +++++++++++---
>> >  1 file changed, 11 insertions(+), 3 deletions(-)
>> >
>> > diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
>> > index bbcc6439a2a1..d5640f3d5276 100644
>> > --- a/drivers/gpu/drm/i915/intel_lrc.c
>> > +++ b/drivers/gpu/drm/i915/intel_lrc.c
>> > @@ -1754,6 +1754,16 @@ static int gen9_init_render_ring(struct intel_engine_cs *engine)
>> >       return init_workarounds_ring(engine);
>> >  }
>> >  
>> > +static void tasklet_kill_and_disable(struct tasklet_struct *t)
>> > +{
>> > +     if (!atomic_read(&t->count))
>> > +             tasklet_kill(t);
>> > +
>> > +     if (atomic_inc_return(&t->count) == 1)
>> > +             tasklet_unlock_wait(t);
>> 
>> You would spin only on the first try regardless. Is this
>> just to prevent one extra spinlock on reset path?
>
> No, the end goal is to prevent a recursive lock.

Ok so you want to be able to call this from inside the
tasklet itself.

On the bigger picture, if the preempt has has already
timeouted and we want to reset, does it matter between
resetting from wq or from timer irq. In another
words what do we gain for this much of added complexity?
-Mika


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