[Mesa-dev] [PATCH 1/4] i965: Track last location of bo used for the batch

[Daniel Vetter]

On Mon, Jun 19, 2017 at 11:06:47AM +0100, Chris Wilson wrote:
> Borrow a trick from anv, and use the last known index for the bo to skip
> a search of the batch->exec_bo when adding a new relocation. In defence
> against the bo being used in multiple batches simultaneously, we check
> that this slot exists and points back to us.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Kenneth Graunke <kenneth at whitecape.org>
> Cc: Matt Turner <mattst88 at gmail.com>
> Cc: Jason Ekstrand <jason.ekstrand at intel.com>
> ---
>  src/mesa/drivers/dri/i965/brw_bufmgr.h        |  5 +++++
>  src/mesa/drivers/dri/i965/intel_batchbuffer.c | 14 ++++++++++++--
>  2 files changed, 17 insertions(+), 2 deletions(-)
> 
> diff --git a/src/mesa/drivers/dri/i965/brw_bufmgr.h b/src/mesa/drivers/dri/i965/brw_bufmgr.h
> index 48488bc33b..dd3a37040a 100644
> --- a/src/mesa/drivers/dri/i965/brw_bufmgr.h
> +++ b/src/mesa/drivers/dri/i965/brw_bufmgr.h
> @@ -76,6 +76,11 @@ struct brw_bo {
>     uint64_t offset64;
>  
>     /**
> +    * Index of this buffer inside the batch, -1 when not in a batch.
> +    */
> +   unsigned int index;
> +
> +   /**
>      * Boolean of whether the GPU is definitely not accessing the buffer.
>      *
>      * This is only valid when reusable, since non-reusable
> diff --git a/src/mesa/drivers/dri/i965/intel_batchbuffer.c b/src/mesa/drivers/dri/i965/intel_batchbuffer.c
> index 62d2fe8ef3..ca7d6b81b1 100644
> --- a/src/mesa/drivers/dri/i965/intel_batchbuffer.c
> +++ b/src/mesa/drivers/dri/i965/intel_batchbuffer.c
> @@ -515,12 +515,20 @@ throttle(struct brw_context *brw)
>     }
>  }
>  
> +#define READ_ONCE(x) (*(volatile __typeof__(x) *)&(x))
> +
>  static void
>  add_exec_bo(struct intel_batchbuffer *batch, struct brw_bo *bo)
>  {
>     if (bo != batch->bo) {
> -      for (int i = 0; i < batch->exec_count; i++) {
> -         if (batch->exec_bos[i] == bo)
> +      unsigned int index = READ_ONCE(bo->index);
> +
> +      if (index < batch->exec_count && batch->exec_bos[index] == bo)
> +         return;
> +
> +      /* May have been shared between multiple active batches */
> +      for (index = 0; index < batch->exec_count; index++) {
> +         if (batch->exec_bos[index] == bo)
>              return;
>        }
>  
> @@ -553,6 +561,7 @@ add_exec_bo(struct intel_batchbuffer *batch, struct brw_bo *bo)
>     validation_entry->rsvd1 = 0;
>     validation_entry->rsvd2 = 0;
>  
> +   bo->index = batch->exec_count;
>     batch->exec_bos[batch->exec_count] = bo;
>     batch->exec_count++;
>     batch->aperture_space += bo->size;
> @@ -597,6 +606,7 @@ execbuffer(int fd,
>        struct brw_bo *bo = batch->exec_bos[i];
>  
>        bo->idle = false;
> +      bo->index = -1;

Since we check for matching backpointer I don't think we even need to
clear this here, but it's cheap. For consistency I think we should also
clear when allocating a bo:


diff --git a/src/mesa/drivers/dri/i965/brw_bufmgr.c b/src/mesa/drivers/dri/i965/brw_bufmgr.c
index da12a131526a..0c3199690257 100644
--- a/src/mesa/drivers/dri/i965/brw_bufmgr.c
+++ b/src/mesa/drivers/dri/i965/brw_bufmgr.c
@@ -325,6 +325,7 @@ retry:
 
       bo->size = bo_size;
       bo->idle = true;
+      bo->index = -1;
 
       memclear(create);
       create.size = bo_size;


With that: Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>

>  
>        /* Update brw_bo::offset64 */
>        if (batch->exec_objects[i].offset != bo->offset64) {
> -- 
> 2.11.0
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch