Re: [PATCH 03/11] drm/i915/execlists: Pull submit after dequeue under timeline lock

From: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
To: Chris Wilson <chris@chris-wilson.co.uk>, intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH 03/11] drm/i915/execlists: Pull submit after dequeue under timeline lock
Date: Fri, 1 Jun 2018 15:02:38 +0100	[thread overview]
Message-ID: <8ed79b89-38ec-2bd3-6ea4-9f97eec43625@linux.intel.com> (raw)
In-Reply-To: <20180531185204.19520-4-chris@chris-wilson.co.uk>

On 31/05/2018 19:51, Chris Wilson wrote:
> In the next patch, we will begin processing the CSB from inside the
> interrupt handler. This means that updating the execlists->port[] will

The message that we will be processing CSB from irq handler, here and in 
following patch 5/11, doesn't seem to be true. So why is this needed? 
Why not just drop some patches from the series?

Regards,

Tvrtko

> no longer be locked by the tasklet but by the engine->timeline.lock
> instead. Pull dequeue and submit under the same lock for protection.
> (An alternative, future, plan is to keep the in/out arrays separate for
> concurrent processing and reduced lock coverage.)
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>   drivers/gpu/drm/i915/intel_lrc.c | 32 ++++++++++++--------------------
>   1 file changed, 12 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index e5cf049c18f8..d207a1bf9dc9 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -562,7 +562,7 @@ static void complete_preempt_context(struct intel_engine_execlists *execlists)
>   	execlists_clear_active(execlists, EXECLISTS_ACTIVE_PREEMPT);
>   }
>   
> -static bool __execlists_dequeue(struct intel_engine_cs *engine)
> +static void __execlists_dequeue(struct intel_engine_cs *engine)
>   {
>   	struct intel_engine_execlists * const execlists = &engine->execlists;
>   	struct execlist_port *port = execlists->port;
> @@ -617,11 +617,11 @@ static bool __execlists_dequeue(struct intel_engine_cs *engine)
>   		 * the HW to indicate that it has had a chance to respond.
>   		 */
>   		if (!execlists_is_active(execlists, EXECLISTS_ACTIVE_HWACK))
> -			return false;
> +			return;
>   
>   		if (need_preempt(engine, last, execlists->queue_priority)) {
>   			inject_preempt_context(engine);
> -			return false;
> +			return;
>   		}
>   
>   		/*
> @@ -646,7 +646,7 @@ static bool __execlists_dequeue(struct intel_engine_cs *engine)
>   		 * priorities of the ports haven't been switch.
>   		 */
>   		if (port_count(&port[1]))
> -			return false;
> +			return;
>   
>   		/*
>   		 * WaIdleLiteRestore:bdw,skl
> @@ -746,8 +746,10 @@ static bool __execlists_dequeue(struct intel_engine_cs *engine)
>   		port != execlists->port ? rq_prio(last) : INT_MIN;
>   
>   	execlists->first = rb;
> -	if (submit)
> +	if (submit) {
>   		port_assign(port, last);
> +		execlists_submit_ports(engine);
> +	}
>   
>   	/* We must always keep the beast fed if we have work piled up */
>   	GEM_BUG_ON(execlists->first && !port_isset(execlists->port));
> @@ -756,24 +758,19 @@ static bool __execlists_dequeue(struct intel_engine_cs *engine)
>   	if (last)
>   		execlists_user_begin(execlists, execlists->port);
>   
> -	return submit;
> +	/* If the engine is now idle, so should be the flag; and vice versa. */
> +	GEM_BUG_ON(execlists_is_active(&engine->execlists,
> +				       EXECLISTS_ACTIVE_USER) ==
> +		   !port_isset(engine->execlists.port));
>   }
>   
>   static void execlists_dequeue(struct intel_engine_cs *engine)
>   {
> -	struct intel_engine_execlists * const execlists = &engine->execlists;
>   	unsigned long flags;
> -	bool submit;
>   
>   	spin_lock_irqsave(&engine->timeline.lock, flags);
> -	submit = __execlists_dequeue(engine);
> +	__execlists_dequeue(engine);
>   	spin_unlock_irqrestore(&engine->timeline.lock, flags);
> -
> -	if (submit)
> -		execlists_submit_ports(engine);
> -
> -	GEM_BUG_ON(port_isset(execlists->port) &&
> -		   !execlists_is_active(execlists, EXECLISTS_ACTIVE_USER));
>   }
>   
>   void
> @@ -1156,11 +1153,6 @@ static void execlists_submission_tasklet(unsigned long data)
>   
>   	if (!execlists_is_active(&engine->execlists, EXECLISTS_ACTIVE_PREEMPT))
>   		execlists_dequeue(engine);
> -
> -	/* If the engine is now idle, so should be the flag; and vice versa. */
> -	GEM_BUG_ON(execlists_is_active(&engine->execlists,
> -				       EXECLISTS_ACTIVE_USER) ==
> -		   !port_isset(engine->execlists.port));
>   }
>   
>   static void queue_request(struct intel_engine_cs *engine,
> 
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