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

[Mika Kuoppala]

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?

-Mika

> +	smp_mb();
> +}
> +
>  static struct i915_request *
>  execlists_reset_prepare(struct intel_engine_cs *engine)
>  {
> @@ -1778,9 +1788,7 @@ execlists_reset_prepare(struct intel_engine_cs *engine)
>  	 * common case of recursively being called from set-wedged from inside
>  	 * i915_reset.
>  	 */
> -	if (!atomic_read(&execlists->tasklet.count))
> -		tasklet_kill(&execlists->tasklet);
> -	tasklet_disable(&execlists->tasklet);
> +	tasklet_kill_and_disable(&execlists->tasklet);
>  
>  	/*
>  	 * We want to flush the pending context switches, having disabled
> -- 
> 2.17.0