Re: [RFC 17/44] drm/i915: Prelude to splitting i915_gem_do_execbuffer in two

Daniel Vetter
2014-07-07T19:21:22Z

On Wed, Jul 02, 2014 at 11:34:23AM -0700, Jesse Barnes wrote:
> On Thu, 26 Jun 2014 18:24:08 +0100
> John.C.Harrison@Intel.com wrote:
>
> > From: John Harrison <John.C.Harrison@Intel.com>
> >
> > The scheduler decouples the submission of batch buffers to the driver with their
> > submission to the hardware. This basically means splitting the execbuffer()
> > function in half. This change rearranges some code ready for the split to occur.
> > ---
> > drivers/gpu/drm/i915/i915_gem_execbuffer.c | 23 ++++++++++++++++-------
> > 1 file changed, 16 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> > index ec274ef..fda9187 100644
> > --- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> > +++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> > @@ -32,6 +32,7 @@
> > #include "i915_trace.h"
> > #include "intel_drv.h"
> > #include <linux/dma_remapping.h>
> > +#include "i915_scheduler.h"
> >
> > #define __EXEC_OBJECT_HAS_PIN (1<<31)
> > #define __EXEC_OBJECT_HAS_FENCE (1<<30)
> > @@ -874,10 +875,7 @@ i915_gem_execbuffer_move_to_gpu(struct intel_engine_cs *ring,
> > if (flush_domains & I915_GEM_DOMAIN_GTT)
> > wmb();
> >
> > - /* Unconditionally invalidate gpu caches and ensure that we do flush
> > - * any residual writes from the previous batch.
> > - */
> > - return intel_ring_invalidate_all_caches(ring);
> > + return 0;
> > }
> >
> > static bool
> > @@ -1219,8 +1217,6 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
> > }
> > }
> >
> > - intel_runtime_pm_get(dev_priv);
> > -
> > ret = i915_mutex_lock_interruptible(dev);
> > if (ret)
> > goto pre_mutex_err;
> > @@ -1331,6 +1327,20 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
> > if (ret)
> > goto err;
> >
> > + i915_gem_execbuffer_move_to_active(&eb->vmas, ring);
> > +
> > + /* To be split into two functions here... */
> > +
> > + intel_runtime_pm_get(dev_priv);
> > +
> > + /* Unconditionally invalidate gpu caches and ensure that we do flush
> > + * any residual writes from the previous batch.
> > + */
> > + ret = intel_ring_invalidate_all_caches(ring);
> > + if (ret)
> > + goto err;
> > +
> > + /* Switch to the correct context for the batch */
> > ret = i915_switch_context(ring, ctx);
> > if (ret)
> > goto err;
> > @@ -1381,7 +1391,6 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
> >
> > trace_i915_gem_ring_dispatch(ring, intel_ring_get_seqno(ring), flags);
> >
> > - i915_gem_execbuffer_move_to_active(&eb->vmas, ring);
> > i915_gem_execbuffer_retire_commands(dev, file, ring, batch_obj);
> >
> > err:
>
> I'd like Chris to take a look too, but it looks safe afaict.
>
> Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>

switch_context can fail with EINTR so we really can't move stuff to the
active list before that point. Or we need to make sure that all the stuff
between the old and new move_to_active callsite can't fail.

Or we need to track this and tell userspace with an EIO and adjusted reset
stats that something between our point of no return where the kernel
committed to executing the batch failed.

Or we need to unrol move_to_active (which is currently not really
possible).
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch