Re: [PATCH 1/3] drm/i915: Trim gen8_irq_handler

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Sep 13, 2017 at 07:18:44PM +0100, Chris Wilson wrote:
> The goal here is to trim an excess posting read and keep the predicates
> tight (reusing the same predicate throughout for GT ack/handling).
> 
> add/remove: 0/0 grow/shrink: 2/1 up/down: 26/-30 (-4)
> function                                     old     new   delta
> gen8_gt_irq_handler                          282     301     +19
> cherryview_irq_handler                       450     457      +7
> gen8_irq_handler                            1653    1623     -30
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_irq.c | 54 +++++++++++++++++++++++------------------
>  1 file changed, 30 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index 91a2c5dbf2da..e12321cb7403 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -1375,31 +1375,34 @@ static irqreturn_t gen8_gt_irq_ack(struct drm_i915_private *dev_priv,
>  }
>  
>  static void gen8_gt_irq_handler(struct drm_i915_private *dev_priv,
> -				u32 gt_iir[4])
> +				u32 master_ctl, u32 gt_iir[4])
>  {
> -	if (gt_iir[0]) {
> +	if (master_ctl & (GEN8_GT_RCS_IRQ | GEN8_GT_BCS_IRQ)) {
>  		gen8_cs_irq_handler(dev_priv->engine[RCS],
>  				    gt_iir[0], GEN8_RCS_IRQ_SHIFT);
>  		gen8_cs_irq_handler(dev_priv->engine[BCS],
>  				    gt_iir[0], GEN8_BCS_IRQ_SHIFT);
>  	}
>  
> -	if (gt_iir[1]) {
> +	if (master_ctl & (GEN8_GT_VCS1_IRQ | GEN8_GT_VCS2_IRQ)) {
>  		gen8_cs_irq_handler(dev_priv->engine[VCS],
>  				    gt_iir[1], GEN8_VCS1_IRQ_SHIFT);
>  		gen8_cs_irq_handler(dev_priv->engine[VCS2],
>  				    gt_iir[1], GEN8_VCS2_IRQ_SHIFT);
>  	}
>  
> -	if (gt_iir[3])
> +	if (master_ctl & GEN8_GT_VECS_IRQ) {
>  		gen8_cs_irq_handler(dev_priv->engine[VECS],
>  				    gt_iir[3], GEN8_VECS_IRQ_SHIFT);
> +	}
>  
> -	if (gt_iir[2] & dev_priv->pm_rps_events)
> -		gen6_rps_irq_handler(dev_priv, gt_iir[2]);
> +	if (master_ctl & (GEN8_GT_PM_IRQ | GEN8_GT_GUC_IRQ)) {
> +		if (gt_iir[2] & dev_priv->pm_rps_events)
> +			gen6_rps_irq_handler(dev_priv, gt_iir[2]);
>  
> -	if (gt_iir[2] & dev_priv->pm_guc_events)
> -		gen9_guc_irq_handler(dev_priv, gt_iir[2]);
> +		if (gt_iir[2] & dev_priv->pm_guc_events)
> +			gen9_guc_irq_handler(dev_priv, gt_iir[2]);
> +	}
>  }
>  
>  static bool bxt_port_hotplug_long_detect(enum port port, u32 val)
> @@ -1984,7 +1987,7 @@ static irqreturn_t cherryview_irq_handler(int irq, void *arg)
>  		I915_WRITE(GEN8_MASTER_IRQ, GEN8_MASTER_IRQ_CONTROL);
>  		POSTING_READ(GEN8_MASTER_IRQ);
>  
> -		gen8_gt_irq_handler(dev_priv, gt_iir);
> +		gen8_gt_irq_handler(dev_priv, master_ctl, gt_iir);
>  
>  		if (hotplug_status)
>  			i9xx_hpd_irq_handler(dev_priv, hotplug_status);
> @@ -2518,36 +2521,39 @@ gen8_de_irq_handler(struct drm_i915_private *dev_priv, u32 master_ctl)
>  	return ret;
>  }
>  
> +#define GEN8_GT_IRQ_BITS (GEN8_GT_RCS_IRQ | GEN8_GT_BCS_IRQ | \
> +			  GEN8_GT_VCS1_IRQ | GEN8_GT_VCS2_IRQ | \
> +			  GEN8_GT_VECS_IRQ | GEN8_GT_PM_IRQ | GEN8_GT_GUC_IRQ)
> +
>  static irqreturn_t gen8_irq_handler(int irq, void *arg)
>  {
> -	struct drm_device *dev = arg;
> -	struct drm_i915_private *dev_priv = to_i915(dev);
> -	u32 master_ctl;
> -	u32 gt_iir[4] = {};
> -	irqreturn_t ret;
> +	struct drm_i915_private *dev_priv = arg;
> +	u32 master_ctl, gt_iir[4];
> +	irqreturn_t ret = IRQ_NONE;
>  
>  	if (!intel_irqs_enabled(dev_priv))
>  		return IRQ_NONE;
>  
> -	master_ctl = I915_READ_FW(GEN8_MASTER_IRQ);
> -	master_ctl &= ~GEN8_MASTER_IRQ_CONTROL;
> +	master_ctl = I915_READ_FW(GEN8_MASTER_IRQ) &  ~GEN8_MASTER_IRQ_CONTROL;
>  	if (!master_ctl)
>  		return IRQ_NONE;
>  
>  	I915_WRITE_FW(GEN8_MASTER_IRQ, 0);
>  
> -	/* IRQs are synced during runtime_suspend, we don't require a wakeref */
> -	disable_rpm_wakeref_asserts(dev_priv);
> -
>  	/* Find, clear, then process each source of interrupt */
> -	ret = gen8_gt_irq_ack(dev_priv, master_ctl, gt_iir);
> -	gen8_gt_irq_handler(dev_priv, gt_iir);
> -	ret |= gen8_de_irq_handler(dev_priv, master_ctl);
> +	if (master_ctl & GEN8_GT_IRQ_BITS)
> +		ret |= gen8_gt_irq_ack(dev_priv, master_ctl, gt_iir);
> +
> +	if (master_ctl & ~GEN8_GT_IRQ_BITS) {
> +		disable_rpm_wakeref_asserts(dev_priv);

Hmm. Why is this needed for DE interrupts but not GT interrupts? Just
the _FW() vs. not in the codepaths? If I'm reading things right we still
have some non _FW() accesses in the RPS handler at least.

BDW+ doesn't suffer from the "hang when accessing the same cacheline from
multiple cpus" issue anymore?

> +		ret |= gen8_de_irq_handler(dev_priv, master_ctl);
> +		enable_rpm_wakeref_asserts(dev_priv);
> +	}

This thing reminds me that I'd still like to split the DE stuff into
ack/handle stuff as well.

>  
>  	I915_WRITE_FW(GEN8_MASTER_IRQ, GEN8_MASTER_IRQ_CONTROL);
> -	POSTING_READ_FW(GEN8_MASTER_IRQ);
>  
> -	enable_rpm_wakeref_asserts(dev_priv);
> +	if (master_ctl & GEN8_GT_IRQ_BITS)
> +		gen8_gt_irq_handler(dev_priv, master_ctl, gt_iir);
>  
>  	return ret;
>  }
> -- 
> 2.14.1
> 
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-- 
Ville Syrjälä
Intel OTC
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