Re: [PATCH 5/6] drm/vc4: Fix overflow mem unreferencing when the binner runs dry.

[Rob Clark]

On Tue, Jul 26, 2016 at 4:47 PM, Eric Anholt <eric@xxxxxxxxxx> wrote:
> Overflow memory handling is tricky: While it's still referenced by the
> BPO registers, we want to keep it from being freed.  When we are
> putting a new set of overflow memory in the registers, we need to
> assign the old one to the last rendering job using it.
>
> We were looking at "what's currently running in the binner", but since
> the bin/render submission split, we may end up with the binner
> completing and having no new job while the renderer is still
> processing.  So, if we don't find a bin job at all, look at the
> highest-seqno (last) render job to attach our overflow to.

so, drive-by comment.. but can you allocate gem bo's without backing
them immediately with pages?  If so, just always allocate the bo
up-front and attach it as a dependency of the batch, and only pin it
to actual pages when you have to overflow?

BR,
-R

> Signed-off-by: Eric Anholt <eric@xxxxxxxxxx>
> Fixes: ca26d28bbaa3 ("drm/vc4: improve throughput by pipelining binning and rendering jobs")
> Cc: stable@xxxxxxxxxxxxxxx
> ---
>  drivers/gpu/drm/vc4/vc4_drv.h | 9 +++++++++
>  drivers/gpu/drm/vc4/vc4_irq.c | 4 +++-
>  2 files changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/vc4/vc4_drv.h b/drivers/gpu/drm/vc4/vc4_drv.h
> index 0ced289d7696..87f727932af2 100644
> --- a/drivers/gpu/drm/vc4/vc4_drv.h
> +++ b/drivers/gpu/drm/vc4/vc4_drv.h
> @@ -321,6 +321,15 @@ vc4_first_render_job(struct vc4_dev *vc4)
>                                 struct vc4_exec_info, head);
>  }
>
> +static inline struct vc4_exec_info *
> +vc4_last_render_job(struct vc4_dev *vc4)
> +{
> +       if (list_empty(&vc4->render_job_list))
> +               return NULL;
> +       return list_last_entry(&vc4->render_job_list,
> +                              struct vc4_exec_info, head);
> +}
> +
>  /**
>   * struct vc4_texture_sample_info - saves the offsets into the UBO for texture
>   * setup parameters.
> diff --git a/drivers/gpu/drm/vc4/vc4_irq.c b/drivers/gpu/drm/vc4/vc4_irq.c
> index b0104a346a74..094bc6a475c1 100644
> --- a/drivers/gpu/drm/vc4/vc4_irq.c
> +++ b/drivers/gpu/drm/vc4/vc4_irq.c
> @@ -83,8 +83,10 @@ vc4_overflow_mem_work(struct work_struct *work)
>
>                 spin_lock_irqsave(&vc4->job_lock, irqflags);
>                 current_exec = vc4_first_bin_job(vc4);
> +               if (!current_exec)
> +                       current_exec = vc4_last_render_job(vc4);
>                 if (current_exec) {
> -                       vc4->overflow_mem->seqno = vc4->finished_seqno + 1;
> +                       vc4->overflow_mem->seqno = current_exec->seqno;
>                         list_add_tail(&vc4->overflow_mem->unref_head,
>                                       &current_exec->unref_list);
>                         vc4->overflow_mem = NULL;
> --
> 2.8.1
>
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