[Mesa-dev] [PATCHv3] r600g: Use a fake reloc to sleep for fences

[Michel Dänzer]

On Fre, 2012-02-03 at 17:32 +0000, Simon Farnsworth wrote: 
> r300g is able to sleep until a fence completes rather than busywait because
> it creates a special buffer object and relocation that stays busy until the
> CS containing the fence is finished.
> 
> Copy the idea into r600g, and use it to sleep if the user asked for an
> infinite wait, falling back to busywaiting if the user provided a timeout.
> 
> Signed-off-by: Simon Farnsworth <simon.farnsworth at onelan.co.uk>
> ---
> 
> v3: At Dave Airlie's suggestion on dri-devel, make use of the BO to give us
> a fighting chance of recovering after a GPU reset.
> 
> We know that the fence will never be signalled by hardware if the dummy BO
> has gone idle - we use that information to escape the loop. This might be a
> useful addition to the 8.0 branch.

That's a nifty trick. :)


> diff --git a/src/gallium/drivers/r600/r600_hw_context.c b/src/gallium/drivers/r600/r600_hw_context.c
> index 8eb8e6d..acfa494 100644
> --- a/src/gallium/drivers/r600/r600_hw_context.c
> +++ b/src/gallium/drivers/r600/r600_hw_context.c
> @@ -1623,6 +1623,13 @@ void r600_context_emit_fence(struct r600_context *ctx, struct r600_resource *fen
>  	ctx->pm4[ctx->pm4_cdwords++] = 0;                       /* DATA_HI */
>  	ctx->pm4[ctx->pm4_cdwords++] = PKT3(PKT3_NOP, 0, 0);
>  	ctx->pm4[ctx->pm4_cdwords++] = r600_context_bo_reloc(ctx, fence_bo, RADEON_USAGE_WRITE);
> +
> +	/* Create a dummy BO so that fence_finish without a timeout can sleep waiting for completion */
> +	*sleep_bo = (struct r600_resource*)
> +			pipe_buffer_create(&ctx->screen->screen, PIPE_BIND_CUSTOM,
> +					   PIPE_USAGE_STAGING, 1);
> +	/* Add the fence as a dummy relocation. */
> +	r600_context_bo_reloc(ctx, *sleep_bo, RADEON_USAGE_READWRITE);

Sorry for only thinking of this now, but what's the advantage of doing
this here, rather than in r600_create_fence()? Seems like that would be
simpler and cleaner.


-- 
Earthling Michel Dänzer           |                   http://www.amd.com
Libre software enthusiast         |          Debian, X and DRI developer