Re: [PATCH] i915: Add support for drm syncobjs

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Quoting Jason Ekstrand (2017-07-05 19:32:21)
> On Wed, Jul 5, 2017 at 10:37 AM, Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> wrote:
> 
>     Quoting Jason Ekstrand (2017-07-05 18:21:22)
>     > This commit adds support for waiting on or signaling DRM syncobjs as
>     > part of execbuf.  It does so by hijacking the currently unused cliprects
>     > pointer to instead point to an array of i915_gem_exec_fence structs
>     > which containe a DRM syncobj and a flags parameter which specifies
>     > whether to wait on it or to signal it.  This implementation
>     > theoretically allows for both flags to be set in which case it waits on
>     > the dma_fence that was in the syncobj and then immediately replaces it
>     > with the dma_fence from the current execbuf.
>     >
>     > Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
>     > ---
>     >
>     > Ideally, I'd like to get whatever kernel reviewing and/or merging is
>     > required to land the userspace bits ASAP.  That said, I understand that
>     > this is my first kernel patch and it's liable to have a few rounds of
>     > review before going in.  :-)
>     >
>     > The mesa branch for using this in Vulkan can be found here:
>     >
>     > https://cgit.freedesktop.org/~jekstrand/mesa/log/?h=review/anv-syncobj
>     >
>     >  drivers/gpu/drm/i915/i915_drv.c            |  3 +-
>     >  drivers/gpu/drm/i915/i915_gem_execbuffer.c | 97
>     ++++++++++++++++++++++++++++--
>     >  include/uapi/drm/i915_drm.h                | 30 ++++++++-
>     >  3 files changed, 121 insertions(+), 9 deletions(-)
>     >
>     > diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_
>     drv.c
>     > index 9167a73..e6f7f49 100644
>     > --- a/drivers/gpu/drm/i915/i915_drv.c
>     > +++ b/drivers/gpu/drm/i915/i915_drv.c
>     > @@ -384,6 +384,7 @@ static int i915_getparam(struct drm_device *dev, void
>     *data,
>     >         case I915_PARAM_HAS_EXEC_FENCE:
>     >         case I915_PARAM_HAS_EXEC_CAPTURE:
>     >         case I915_PARAM_HAS_EXEC_BATCH_FIRST:
>     > +       case I915_PARAM_HAS_EXEC_FENCE_ARRAY:
>     >                 /* For the time being all of these are always true;
>     >                  * if some supported hardware does not have one of these
>     >                  * features this value needs to be provided from
>     > @@ -2734,7 +2735,7 @@ static struct drm_driver driver = {
>     >          */
>     >         .driver_features =
>     >             DRIVER_HAVE_IRQ | DRIVER_IRQ_SHARED | DRIVER_GEM |
>     DRIVER_PRIME |
>     > -           DRIVER_RENDER | DRIVER_MODESET | DRIVER_ATOMIC,
>     > +           DRIVER_RENDER | DRIVER_MODESET | DRIVER_ATOMIC |
>     DRIVER_SYNCOBJ,
>     >         .release = i915_driver_release,
>     >         .open = i915_driver_open,
>     >         .lastclose = i915_driver_lastclose,
>     > diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm
>     /i915/i915_gem_execbuffer.c
>     > index 929f275..81b7b7b 100644
>     > --- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
>     > +++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
>     > @@ -33,6 +33,7 @@
>     >
>     >  #include <drm/drmP.h>
>     >  #include <drm/i915_drm.h>
>     > +#include <drm/drm_syncobj.h>
>     >
>     >  #include "i915_drv.h"
>     >  #include "i915_gem_clflush.h"
>     > @@ -1882,8 +1883,10 @@ static bool i915_gem_check_execbuffer(struct
>     drm_i915_gem_execbuffer2 *exec)
>     >                 return false;
>     >
>     >         /* Kernel clipping was a DRI1 misfeature */
>     > -       if (exec->num_cliprects || exec->cliprects_ptr)
>     > -               return false;
>     > +       if (!(exec->flags & I915_EXEC_FENCE_ARRAY)) {
>     > +               if (exec->num_cliprects || exec->cliprects_ptr)
>     > +                       return false;
>     > +       }
>     >
>     >         if (exec->DR4 == 0xffffffff) {
>     >                 DRM_DEBUG("UXA submitting garbage DR4, fixing up\n");
>     > @@ -2118,12 +2121,15 @@ static int
>     >  i915_gem_do_execbuffer(struct drm_device *dev,
>     >                        struct drm_file *file,
>     >                        struct drm_i915_gem_execbuffer2 *args,
>     > -                      struct drm_i915_gem_exec_object2 *exec)
>     > +                      struct drm_i915_gem_exec_object2 *exec,
>     > +                      struct drm_i915_gem_exec_fence *fences)
>     >  {
>     >         struct i915_execbuffer eb;
>     >         struct dma_fence *in_fence = NULL;
>     >         struct sync_file *out_fence = NULL;
>     > +       struct drm_syncobj **syncobjs = NULL;
>     >         int out_fence_fd = -1;
>     > +       unsigned int i;
>     >         int err;
>     >
>     >         BUILD_BUG_ON(__EXEC_OBJECT_INTERNAL_FLAGS &
>     > @@ -2186,9 +2192,30 @@ i915_gem_do_execbuffer(struct drm_device *dev,
>     >                 }
>     >         }
>     >
>     > +       if (args->flags & I915_EXEC_FENCE_ARRAY) {
>     > +               syncobjs = kvmalloc_array(args->num_cliprects,
>     > +                                         sizeof(*syncobjs),
>     > +                                         __GFP_NOWARN | GFP_TEMPORARY |
>     > +                                         __GFP_ZERO);
>     > +               if (syncobjs == NULL) {
>     > +                       DRM_DEBUG("Failed to allocate array of %d
>     syncobjs\n",
>     > +                                 args->num_cliprects);
>     > +                       err = -ENOMEM;
>     > +                       goto err_out_fence;
>     > +               }
>     > +               for (i = 0; i < args->num_cliprects; i++) {
>     > +                       syncobjs[i] = drm_syncobj_find(file, fences
>     [i].handle);
>     > +                       if (!syncobjs[i]) {
>     > +                               DRM_DEBUG("Invalid syncobj handle
>     provided\n");
>     > +                               err = -EINVAL;
>     > +                               goto err_syncobjs;
>     > +                       }
>     > +               }
> 
>     I did this in the caller so that we only allocated and passed in a single
>     array of drm_syncobj (with the flags packed into the low bits).
> 
> 
> Packing things into the low bits seems a bit sketchy but it works so long as we
> only have the two flag bits.
>  
> 
>     > +       }
>     > +
>     >         err = eb_create(&eb);
>     >         if (err)
>     > -               goto err_out_fence;
>     > +               goto err_syncobjs;
>     >
>     >         GEM_BUG_ON(!eb.lut_size);
>     >
>     > @@ -2304,6 +2331,16 @@ i915_gem_do_execbuffer(struct drm_device *dev,
>     >                         goto err_request;
>     >         }
>     >
>     > +       if (args->flags & I915_EXEC_FENCE_ARRAY) {
>     > +               for (i = 0; i < args->num_cliprects; i++) {
>     > +                       if (fences[i].flags & I915_EXEC_FENCE_WAIT) {
>     > +                               if (i915_gem_request_await_dma_fence
>     (eb.request,
>     > +                                                                   
>     syncobjs[i]->fence))
>     > +                                       goto err_request;
>     > +                       }
>     > +               }
>     > +       }
>     > +
>     >         if (out_fence_fd != -1) {
>     >                 out_fence = sync_file_create(&eb.request->fence);
>     >                 if (!out_fence) {
>     > @@ -2312,6 +2349,20 @@ i915_gem_do_execbuffer(struct drm_device *dev,
>     >                 }
>     >         }
>     >
>     > +    /* We need to add fences to syncobjs last because doing so mutates
>     the
>     > +     * syncobj and we have no good way to recover if the execbuf fails
>     > +     * after this point.  Fortunately, drm_syncobj_replace_fence can
>     never
>     > +     * fail.
>     > +     */
>     > +       if (args->flags & I915_EXEC_FENCE_ARRAY) {
>     > +               for (i = 0; i < args->num_cliprects; i++) {
>     > +                       if (fences[i].flags & I915_EXEC_FENCE_SIGNAL) {
>     > +                               drm_syncobj_replace_fence(file, syncobjs
>     [i],
>     > +                                                         &eb.request->
>     fence);
>     > +                       }
>     > +               }
>     > +       }
>     > +
> 
>     This has to be after the execbuf is submitted, next to where out_fence
>     is attached is a good spot, and should only be updated on success. (The
>     kernel API allows combining of FENCE_WAIT | FENCE_SIGNAL so we can only
>     replace a FENCE_WAIT once we know we have committed the execbuf.)
> 
> 
> It's currently right after we call
> 
>         out_fence = sync_file_create(&eb.request->fence);

That's where we create the out fence, not where we attach it to the
request, see the fd_install, which is after we have successfully
committed the request.
 
> which is before eb_submit().  Are sync files wrong?  Note that I was careful to
> ensure that there are no error paths after syncobj_replace_fence so we know for
> 100% sure that it will be committed, hence the comment.

There's the rather big one in eb_submit() that will generate EINTR for
your pain.

>     I moved all of these to little functions: get_fence_array,
>     await_fence_array, signal_fence_array and put_fence_array.
> 
> 
> You clearly have a version of this patch somewhere.  Where can I find it?

It's still on the older syncobj api, I am easily distracted. :|
-Chris
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