Re: [Intel-gfx] [PATCH] drm/i915/pmu: Stop peeking at kernel internals for counting interrupts

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

On Thu, Dec 10, 2020 at 05:35:45PM +0000, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> 
> Peeking at kernel internals is bad taste so instead we keep our own
> counter which also solves the problem of shared interrupt lines.
> 
> Additional cost should be way below noise relative to mmio reads.
> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Suggested-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_drv.h |  3 +++
>  drivers/gpu/drm/i915/i915_irq.c | 16 ++++++++++++++++
>  drivers/gpu/drm/i915/i915_pmu.c | 19 +------------------
>  3 files changed, 20 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 5d04b282c060..de5cdcdc46b0 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -889,6 +889,9 @@ struct drm_i915_private {
>  	/* protects the irq masks */
>  	spinlock_t irq_lock;
>  
> +	/** Overall irq handler invocations. */
> +	u64 irq_count;
> +
>  	bool display_irqs_enabled;
>  
>  	/* To control wakeup latency, e.g. for irq-driven dp aux transfers. */
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index b245109f73e3..a88c1da025f1 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -1596,6 +1596,8 @@ static irqreturn_t valleyview_irq_handler(int irq, void *arg)
>  	if (!intel_irqs_enabled(dev_priv))
>  		return IRQ_NONE;
>  
> +	dev_priv->irq_count++;

Would rather have to be something like
if (ret == IRQ_HANDLED)
	irq_count++;

if we really wanted to count only our interrupts when the
irq line is shared.

-- 
Ville Syrjälä
Intel
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