[PATCH 3/3] drm/panfrost: Stay in the threaded MMU IRQ handler until we've handled all IRQs

[Steven Price]

On 01/02/2021 12:59, Boris Brezillon wrote:
> On Mon, 1 Feb 2021 12:13:49 +0000
> Steven Price <steven.price at arm.com> wrote:
> 
>> On 01/02/2021 08:21, Boris Brezillon wrote:
>>> Doing a hw-irq -> threaded-irq round-trip is counter-productive, stay
>>> in the threaded irq handler as long as we can.
>>>
>>> Signed-off-by: Boris Brezillon <boris.brezillon at collabora.com>
>>
>> Looks fine to me, but I'm interested to know if you actually saw a
>> performance improvement. Back-to-back MMU faults should (hopefully) be
>> fairly uncommon.
> 
> I actually didn't check the perf improvement or the actual number of
> back-to-back MMU faults, but
> dEQP-GLES31.functional.draw_indirect.compute_interop.large.drawelements_combined_grid_1000x1000_drawcount_5000
> seemed to generate a few of those, so I thought it'd be good to
> optimize that case given how trivial it is.

Fair enough! I was just a little concerned that Panfrost was somehow 
provoking enough interrupts that this was a measurable performance 
improvement.

I assume you'll push these to drm-misc-next (/fixes) as appropriate.

Thanks,

Steve

>>
>> Regardless:
>>
>> Reviewed-by: Steven Price <steven.price at arm.com>
>>
>>> ---
>>>    drivers/gpu/drm/panfrost/panfrost_mmu.c | 7 +++++++
>>>    1 file changed, 7 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c
>>> index 21e552d1ac71..65bc20628c4e 100644
>>> --- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
>>> +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
>>> @@ -580,6 +580,8 @@ static irqreturn_t panfrost_mmu_irq_handler_thread(int irq, void *data)
>>>    	u32 status = mmu_read(pfdev, MMU_INT_RAWSTAT);
>>>    	int i, ret;
>>>    
>>> +again:
>>> +
>>>    	for (i = 0; status; i++) {
>>>    		u32 mask = BIT(i) | BIT(i + 16);
>>>    		u64 addr;
>>> @@ -628,6 +630,11 @@ static irqreturn_t panfrost_mmu_irq_handler_thread(int irq, void *data)
>>>    		status &= ~mask;
>>>    	}
>>>    
>>> +	/* If we received new MMU interrupts, process them before returning. */
>>> +	status = mmu_read(pfdev, MMU_INT_RAWSTAT);
>>> +	if (status)
>>> +		goto again;
>>> +
>>>    	mmu_write(pfdev, MMU_INT_MASK, ~0);
>>>    	return IRQ_HANDLED;
>>>    };
>>>    
>>
>