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SubjectRe: [PATCH 1/2] drm/msm: Handle ringbuffer overflow
On Wed, Nov 24, 2021 at 11:36 PM Dmitry Baryshkov
<dmitry.baryshkov@linaro.org> wrote:
>
> On 28/04/2021 22:36, Rob Clark wrote:
> > From: Rob Clark <robdclark@chromium.org>
> >
> > Currently if userspace manages to fill up the ring faster than the GPU
> > can consume we (a) spin for up to 1sec, and then (b) overwrite the
> > ringbuffer contents from previous submits that the GPU is still busy
> > executing. Which predictably goes rather badly.
> >
> > Instead, just skip flushing (updating WPTR) and reset ring->next back to
> > where it was before we tried writing the submit into the ringbuffer, and
> > return an error to userspace (which can then try again).
> >
> > Signed-off-by: Rob Clark <robdclark@chromium.org>
>
> Rob, you've posted this patch, but never merged it. Should it be merged
> at some point?

I think it is a bit less needed now, since drm/sched will limit the #
of in-flight submits (when I sent that patch, it was before conversion
to use drm/sched)

With a bit more locking re-work we could do something more clever like
just blocking until there is space in the ringbuffer.. but aren't
there quite yet.

BR,
-R

>
> > ---
> > drivers/gpu/drm/msm/adreno/a5xx_gpu.c | 3 +++
> > drivers/gpu/drm/msm/adreno/a6xx_gpu.c | 3 +++
> > drivers/gpu/drm/msm/adreno/adreno_gpu.c | 24 +++++++++++++++++-
> > drivers/gpu/drm/msm/msm_gem_submit.c | 7 +++++-
> > drivers/gpu/drm/msm/msm_gpu.c | 33 +++++++++++++++++++++++--
> > drivers/gpu/drm/msm/msm_gpu.h | 2 +-
> > drivers/gpu/drm/msm/msm_ringbuffer.h | 5 ++++
> > 7 files changed, 72 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/adreno/a5xx_gpu.c b/drivers/gpu/drm/msm/adreno/a5xx_gpu.c
> > index ce13d49e615b..0c8faad3b328 100644
> > --- a/drivers/gpu/drm/msm/adreno/a5xx_gpu.c
> > +++ b/drivers/gpu/drm/msm/adreno/a5xx_gpu.c
> > @@ -36,6 +36,9 @@ void a5xx_flush(struct msm_gpu *gpu, struct msm_ringbuffer *ring,
> > OUT_RING(ring, upper_32_bits(shadowptr(a5xx_gpu, ring)));
> > }
> >
> > + if (unlikely(ring->overflow))
> > + return;
> > +
> > spin_lock_irqsave(&ring->preempt_lock, flags);
> >
> > /* Copy the shadow to the actual register */
> > diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> > index d553f62f4eeb..4a4728a774c0 100644
> > --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> > +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> > @@ -68,6 +68,9 @@ static void a6xx_flush(struct msm_gpu *gpu, struct msm_ringbuffer *ring)
> > OUT_RING(ring, upper_32_bits(shadowptr(a6xx_gpu, ring)));
> > }
> >
> > + if (unlikely(ring->overflow))
> > + return;
> > +
> > spin_lock_irqsave(&ring->preempt_lock, flags);
> >
> > /* Copy the shadow to the actual register */
> > diff --git a/drivers/gpu/drm/msm/adreno/adreno_gpu.c b/drivers/gpu/drm/msm/adreno/adreno_gpu.c
> > index 0f184c3dd9d9..a658777e07b1 100644
> > --- a/drivers/gpu/drm/msm/adreno/adreno_gpu.c
> > +++ b/drivers/gpu/drm/msm/adreno/adreno_gpu.c
> > @@ -467,6 +467,9 @@ void adreno_flush(struct msm_gpu *gpu, struct msm_ringbuffer *ring, u32 reg)
> > {
> > uint32_t wptr;
> >
> > + if (unlikely(ring->overflow))
> > + return;
> > +
> > /* Copy the shadow to the actual register */
> > ring->cur = ring->next;
> >
> > @@ -788,12 +791,31 @@ static uint32_t ring_freewords(struct msm_ringbuffer *ring)
> > return (rptr + (size - 1) - wptr) % size;
> > }
> >
> > +static bool space_avail(struct msm_ringbuffer *ring, uint32_t ndwords)
> > +{
> > + if (ring_freewords(ring) >= ndwords)
> > + return true;
> > +
> > + /* We don't have a good way to know in general when the RPTR has
> > + * advanced.. newer things that use CP_WHERE_AM_I to update the
> > + * shadow rptr could possibly insert a packet to generate an irq.
> > + * But that doesn't cover older GPUs. But if the ringbuffer is
> > + * full, it could take a while before it is empty again, so just
> > + * insert a blind sleep to avoid a busy loop.
> > + */
> > + msleep(1);
> > +
> > + return false;
> > +}
> > +
> > void adreno_wait_ring(struct msm_ringbuffer *ring, uint32_t ndwords)
> > {
> > - if (spin_until(ring_freewords(ring) >= ndwords))
> > + if (spin_until(space_avail(ring, ndwords))) {
> > DRM_DEV_ERROR(ring->gpu->dev->dev,
> > "timeout waiting for space in ringbuffer %d\n",
> > ring->id);
> > + ring->overflow = true;
> > + }
> > }
> >
> > /* Get legacy powerlevels from qcom,gpu-pwrlevels and populate the opp table */
> > diff --git a/drivers/gpu/drm/msm/msm_gem_submit.c b/drivers/gpu/drm/msm/msm_gem_submit.c
> > index 5480852bdeda..4bc669460fda 100644
> > --- a/drivers/gpu/drm/msm/msm_gem_submit.c
> > +++ b/drivers/gpu/drm/msm/msm_gem_submit.c
> > @@ -683,6 +683,9 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
> > submitid = atomic_inc_return(&ident) - 1;
> >
> > ring = gpu->rb[queue->prio];
> > +
> > + GEM_WARN_ON(ring->overflow);
> > +
> > trace_msm_gpu_submit(pid_nr(pid), ring->id, submitid,
> > args->nr_bos, args->nr_cmds);
> >
> > @@ -829,7 +832,9 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
> > }
> > }
> >
> > - msm_gpu_submit(gpu, submit);
> > + ret = msm_gpu_submit(gpu, submit);
> > + if (ret)
> > + goto out;
> >
> > args->fence = submit->fence->seqno;
> >
> > diff --git a/drivers/gpu/drm/msm/msm_gpu.c b/drivers/gpu/drm/msm/msm_gpu.c
> > index ab7c167b0623..7655ad9108c8 100644
> > --- a/drivers/gpu/drm/msm/msm_gpu.c
> > +++ b/drivers/gpu/drm/msm/msm_gpu.c
> > @@ -787,7 +787,7 @@ void msm_gpu_retire(struct msm_gpu *gpu)
> > }
> >
> > /* add bo's to gpu's ring, and kick gpu: */
> > -void msm_gpu_submit(struct msm_gpu *gpu, struct msm_gem_submit *submit)
> > +int msm_gpu_submit(struct msm_gpu *gpu, struct msm_gem_submit *submit)
> > {
> > struct drm_device *dev = gpu->dev;
> > struct msm_drm_private *priv = dev->dev_private;
> > @@ -834,9 +834,38 @@ void msm_gpu_submit(struct msm_gpu *gpu, struct msm_gem_submit *submit)
> > spin_unlock(&ring->submit_lock);
> >
> > gpu->funcs->submit(gpu, submit);
> > - priv->lastctx = submit->queue->ctx;
> >
> > hangcheck_timer_reset(gpu);
> > +
> > + if (unlikely(ring->overflow)) {
> > + /*
> > + * Reset the ptr back to before the submit, so the GPU
> > + * doesn't see a partial submit:
> > + */
> > + ring->next = ring->cur;
> > +
> > + /*
> > + * Clear the overflow flag, hopefully the next submit on
> > + * the ring actually fits
> > + */
> > + ring->overflow = false;
> > +
> > + /*
> > + * One might be tempted to remove the submit from the
> > + * submits list, and drop it's reference (and drop the
> > + * active reference for all the bos). But we can't
> > + * really signal the fence attached to obj->resv without
> > + * disturbing other fences on the timeline. So instead
> > + * just leave it and let it retire normally when a
> > + * later submit completes.
> > + */
> > +
> > + return -ENOSPC;
> > + }
> > +
> > + priv->lastctx = submit->queue->ctx;
> > +
> > + return 0;
> > }
> >
> > /*
> > diff --git a/drivers/gpu/drm/msm/msm_gpu.h b/drivers/gpu/drm/msm/msm_gpu.h
> > index d7cd02cd2109..2dd2ef1f8328 100644
> > --- a/drivers/gpu/drm/msm/msm_gpu.h
> > +++ b/drivers/gpu/drm/msm/msm_gpu.h
> > @@ -302,7 +302,7 @@ int msm_gpu_perfcntr_sample(struct msm_gpu *gpu, uint32_t *activetime,
> > uint32_t *totaltime, uint32_t ncntrs, uint32_t *cntrs);
> >
> > void msm_gpu_retire(struct msm_gpu *gpu);
> > -void msm_gpu_submit(struct msm_gpu *gpu, struct msm_gem_submit *submit);
> > +int msm_gpu_submit(struct msm_gpu *gpu, struct msm_gem_submit *submit);
> >
> > int msm_gpu_init(struct drm_device *drm, struct platform_device *pdev,
> > struct msm_gpu *gpu, const struct msm_gpu_funcs *funcs,
> > diff --git a/drivers/gpu/drm/msm/msm_ringbuffer.h b/drivers/gpu/drm/msm/msm_ringbuffer.h
> > index fe55d4a1aa16..d8ad9818c389 100644
> > --- a/drivers/gpu/drm/msm/msm_ringbuffer.h
> > +++ b/drivers/gpu/drm/msm/msm_ringbuffer.h
> > @@ -40,6 +40,8 @@ struct msm_ringbuffer {
> > struct drm_gem_object *bo;
> > uint32_t *start, *end, *cur, *next;
> >
> > + bool overflow;
> > +
> > /*
> > * List of in-flight submits on this ring. Protected by submit_lock.
> > */
> > @@ -69,6 +71,9 @@ void msm_ringbuffer_destroy(struct msm_ringbuffer *ring);
> > static inline void
> > OUT_RING(struct msm_ringbuffer *ring, uint32_t data)
> > {
> > + if (ring->overflow)
> > + return;
> > +
> > /*
> > * ring->next points to the current command being written - it won't be
> > * committed as ring->cur until the flush
> >
>
>
> --
> With best wishes
> Dmitry

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