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

[Boris Brezillon <boris.brezillon@collabora.com>]

On Mon, 1 Feb 2021 12:13:49 +0000
Steven Price <steven.price@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@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.

> 
> Regardless:
> 
> Reviewed-by: Steven Price <steven.price@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;
> >   };
> >   
> 

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