Re: [PATCH v2 2/2] drm/vc4: Allocated/liberate the binner BO at firstopen/lastclose

From: Eric Anholt <eric@anholt.net>
To: Paul Kocialkowski <paul.kocialkowski@bootlin.com>,
	dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	Maxime Ripard <maxime.ripard@bootlin.com>,
	Sean Paul <sean@poorly.run>, David Airlie <airlied@linux.ie>,
	Daniel Vetter <daniel@ffwll.ch>,
	Eben Upton <eben@raspberrypi.org>,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Subject: Re: [PATCH v2 2/2] drm/vc4: Allocated/liberate the binner BO at firstopen/lastclose
Date: Wed, 20 Mar 2019 09:58:27 -0700	[thread overview]
Message-ID: <87wokth498.fsf@anholt.net> (raw)
In-Reply-To: <20190320154809.14823-3-paul.kocialkowski@bootlin.com>

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Paul Kocialkowski <paul.kocialkowski@bootlin.com> writes:

> The binner BO is a pre-requisite to GPU operations, so we must ensure
> that it is always allocated when the GPU is in use. Currently, we are
> allocating it at probe time and liberating/allocating it during runtime
> pm cycles.
>
> First, since the binner buffer is only required for GPU rendering, it's
> a waste to allocate it when the driver probes since internal users of
> the driver (such as fbcon) won't try to use the GPU.
>
> Move the allocation/liberation to the firstopen/lastclose instead to
> only allocate it when userspace has opened the device and adapt the IRQ
> handler to return early when no binner BO was allocated yet.
>
> Second, because the buffer is allocated from the same pool as other GPU
> buffers, we might run into a situation where we are out of memory at
> runtime resume. This causes the binner BO allocation to fail and results
> in all subsequent operations to fail, resulting in a major hang in
> userspace.
>
> As a result, keep the buffer alive during runtime pm.
>
> Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
> ---

> diff --git a/drivers/gpu/drm/vc4/vc4_irq.c b/drivers/gpu/drm/vc4/vc4_irq.c
> index 4cd2ccfe15f4..efaba2b02f6c 100644
> --- a/drivers/gpu/drm/vc4/vc4_irq.c
> +++ b/drivers/gpu/drm/vc4/vc4_irq.c
> @@ -64,6 +64,9 @@ vc4_overflow_mem_work(struct work_struct *work)
>  	struct vc4_exec_info *exec;
>  	unsigned long irqflags;
>  
> +	if (!bo)
> +		return;
> +
>  	bin_bo_slot = vc4_v3d_get_bin_slot(vc4);
>  	if (bin_bo_slot < 0) {
>  		DRM_ERROR("Couldn't allocate binner overflow mem\n");

Hmm.  We take the OOM IRQ on poweron, have no bin BO since nobody's
opened yet, and leave it.  Do we ever get the OOM IRQ again after that?
Seems like vc4_allocate_bin_bo() might need to kick something so that we
can fill an OOM request.

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