[Mesa-dev] [Intel-gfx] [PATCH] i965: Use default contexts when possible.

[Ben Widawsky]

On Thu, Jan 02, 2014 at 07:50:35PM -1000, Ben Widawsky wrote:
> Will full PPGTT support it can be assumed that every file descriptor
> gets its own hardware context. As such, there is no need to allocate
> anew context in order to use the features provided by hardware contexts.
> Eliminating this extra context allocation saves both physical memory
> (currently PPGTT pages are pinned forever), GGTT space on IVB, and HSW,
> as well as the associated startup cost of allocating the second context
> - which can include an eviction in pathological cases.
> 
> Unfortunately, this requires a libdrm version bump as it requires a new
> interface.
> 
> NOTE: I am uncertain if the share context idea is valid. Needs mesa
> eyes.
> 
> Cc: Kenneth Graunke <kenneth.w.graunke at intel.com>
> Signed-off-by: Ben Widawsky <ben at bwidawsk.net>

Hi Ken/whomever. Everything but the actual exposing of the full PPGTT
param from this series has been merged. If you can give me a pointer on
what needs doing here in mesa, I'll try again now that full PPGTT is
available in dinq.

Thanks.

> ---
>  configure.ac                            | 2 +-
>  src/mesa/drivers/dri/i965/brw_context.c | 9 ++++++++-
>  2 files changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/configure.ac b/configure.ac
> index f75325d..a0ae0b3 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -29,7 +29,7 @@ AC_SUBST([OSMESA_VERSION])
>  dnl Versions for external dependencies
>  LIBDRM_REQUIRED=2.4.24
>  LIBDRM_RADEON_REQUIRED=2.4.50
> -LIBDRM_INTEL_REQUIRED=2.4.49
> +LIBDRM_INTEL_REQUIRED=2.4.51
>  LIBDRM_NVVIEUX_REQUIRED=2.4.33
>  LIBDRM_NOUVEAU_REQUIRED="2.4.33 libdrm >= 2.4.41"
>  LIBDRM_FREEDRENO_REQUIRED=2.4.39
> diff --git a/src/mesa/drivers/dri/i965/brw_context.c b/src/mesa/drivers/dri/i965/brw_context.c
> index 78c06fc..f5a66e1 100644
> --- a/src/mesa/drivers/dri/i965/brw_context.c
> +++ b/src/mesa/drivers/dri/i965/brw_context.c
> @@ -674,7 +674,14 @@ brwCreateContext(gl_api api,
>  
>     intel_fbo_init(brw);
>  
> -   if (brw->gen >= 6) {
> +   /* We assume that the hw_ctx is the first created for the file descriptor if
> +    * this is not a share context. If that assumption turns false then we'll
> +    * end up having hw_ctx for two contexts using the same actual context.
> +    */
> +   if (!shareCtx)
> +      brw->hw_ctx = drm_intel_gem_default_context_get(brw->bufmgr);
> +
> +   if (!brw->hw_ctx && brw->gen >= 6) {
>        /* Create a new hardware context.  Using a hardware context means that
>         * our GPU state will be saved/restored on context switch, allowing us
>         * to assume that the GPU is in the same state we left it in.
> -- 
> 1.8.5.2
> 
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-- 
Ben Widawsky, Intel Open Source Technology Center