Re: [PATCH v2 1/5] drm/i915: Only disable execlist preemption for the duration of the request

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

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

> We need to prevent resubmission of the context immediately following an
> initial resubmit (which does a lite-restore preemption). Currently we do
> this by disabling all submission whilst the context is still active, but
> we can improve this by limiting the restriction to only until we
> receive notification from the context-switch interrupt that the
> lite-restore preemption is complete.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

With some handholding in irc, I can now associate the past, the
code and the commit desc and it holds true.

I also tested it lightly with kbl.

Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>

> ---
>  drivers/gpu/drm/i915/i915_debugfs.c     | 18 ++++++++++++------
>  drivers/gpu/drm/i915/intel_lrc.c        |  7 +++----
>  drivers/gpu/drm/i915/intel_ringbuffer.h |  1 -
>  3 files changed, 15 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index fa69d72fdcb9..9d7a77ecec3d 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -3320,15 +3320,21 @@ static int i915_engine_info(struct seq_file *m, void *unused)
>  
>  			rcu_read_lock();
>  			rq = READ_ONCE(engine->execlist_port[0].request);
> -			if (rq)
> -				print_request(m, rq, "\t\tELSP[0] ");
> -			else
> +			if (rq) {
> +				seq_printf(m, "\t\tELSP[0] count=%d, ",
> +					   engine->execlist_port[0].count);
> +				print_request(m, rq, "rq: ");
> +			} else {
>  				seq_printf(m, "\t\tELSP[0] idle\n");
> +			}
>  			rq = READ_ONCE(engine->execlist_port[1].request);
> -			if (rq)
> -				print_request(m, rq, "\t\tELSP[1] ");
> -			else
> +			if (rq) {
> +				seq_printf(m, "\t\tELSP[1] count=%d, ",
> +					   engine->execlist_port[1].count);
> +				print_request(m, rq, "rq: ");
> +			} else {
>  				seq_printf(m, "\t\tELSP[1] idle\n");
> +			}
>  			rcu_read_unlock();
>  
>  			spin_lock_irq(&engine->timeline->lock);
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index eceffe25c022..873c3a8a580b 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -388,7 +388,7 @@ static void execlists_submit_ports(struct intel_engine_cs *engine)
>  		execlists_context_status_change(port[0].request,
>  						INTEL_CONTEXT_SCHEDULE_IN);
>  	desc[0] = execlists_update_context(port[0].request);
> -	engine->preempt_wa = port[0].count++; /* bdw only? fixed on skl? */
> +	port[0].count++;
>  
>  	if (port[1].request) {
>  		GEM_BUG_ON(port[1].count);
> @@ -558,7 +558,8 @@ static bool execlists_elsp_ready(struct intel_engine_cs *engine)
>  	int port;
>  
>  	port = 1; /* wait for a free slot */
> -	if (engine->disable_lite_restore_wa || engine->preempt_wa)
> +	if (engine->disable_lite_restore_wa ||
> +	    engine->execlist_port[0].count > 1)
>  		port = 0; /* wait for GPU to be idle before continuing */
>  
>  	return !engine->execlist_port[port].request;
> @@ -609,8 +610,6 @@ static void intel_lrc_irq_handler(unsigned long data)
>  				i915_gem_request_put(port[0].request);
>  				port[0] = port[1];
>  				memset(&port[1], 0, sizeof(port[1]));
> -
> -				engine->preempt_wa = false;
>  			}
>  
>  			GEM_BUG_ON(port[0].count == 0 &&
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
> index 79c2b8d72322..34cdbb6350a8 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.h
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
> @@ -381,7 +381,6 @@ struct intel_engine_cs {
>  	struct rb_node *execlist_first;
>  	unsigned int fw_domains;
>  	bool disable_lite_restore_wa;
> -	bool preempt_wa;
>  	u32 ctx_desc_template;
>  
>  	/* Contexts are pinned whilst they are active on the GPU. The last
> -- 
> 2.11.0
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