[Intel-gfx] [PATCH 1/4] drm/i915/execlists: Kick start request processing after a reset

[Michał Winiarski]

On Sat, Sep 16, 2017 at 09:44:11PM +0100, Chris Wilson wrote:
> During a reset, we may skip over completed requests and lost
> context-switch interrupts. Following the reset, we may then may end up
> with no active requests in the ELSP (and so do not resubmit to restart
> the engine), but have a queue of requests ready for execution. This is
> unlikely, it requires the last request to complete after the hang is
> detected, but not impossible. The outcome of this is that the engine
> stalls, possibly leading to full ring and indefinite wait under
> struct_mutex, eventually leading to a full driver hang.
> 
> Alternatively, we can solve this by unsubmitting the incomplete requests
> and just kickstarting the tasklet. Michał has patches for that, which I
> initially disliked due to the extra complexity, but the complexity of
> this "simple" restart is growing...

You are doing exactly that in 4/4.
Perhaps squash the two together to avoid moving code around, although this one
is a genuine fix, so I guess it's also fine on its own.
If you rebase the whole thing on top of coalesced GuC requests (which now is all
reviewed and ready to be merged), we'll have uniform reset handling for GuC
and execlists.

> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Michał Winiarski <michal.winiarski at intel.com>
> Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

Reviewed-by: Michał Winiarski <michal.winiarski at intel.com>

-Michał

> ---
>  drivers/gpu/drm/i915/intel_lrc.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 2f9ebd32025c..d960611692de 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -1340,8 +1340,12 @@ static int gen8_init_common_ring(struct intel_engine_cs *engine)
>  		submit = true;
>  	}
>  
> -	if (submit && !i915.enable_guc_submission)
> -		execlists_submit_ports(engine);
> +	if (!i915.enable_guc_submission) {
> +		if (submit)
> +			execlists_submit_ports(engine);
> +		else if (engine->execlist_first)
> +			tasklet_hi_schedule(&engine->irq_tasklet);
> +	}
>  
>  	return 0;
>  }
> -- 
> 2.14.1
>