[Intel-gfx] [PATCH 07/18] drm/i915: Combine tasklet_kill and tasklet_disable

[Chris Wilson]

Quoting Mika Kuoppala (2018-04-24 13:26:11)
> Chris Wilson <chris at 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 at chris-wilson.co.uk>
> > Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> > Cc: Michał Winiarski <michal.winiarski at intel.com>
> > CC: Michel Thierry <michel.thierry at intel.com>
> > Cc: Jeff McGee <jeff.mcgee at 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.
-Chris