Re: [PATCH] drm/i915: Prefer setting PTE cache age to 3

[Jesse Barnes <jbarnes@virtuousgeek.org>]

On Fri, 22 Nov 2013 10:37:53 +0000
Chris Wilson <chris@chris-wilson.co.uk> wrote:

> We have conflicting benchmark data that suggest either age 0 or age 3 is
> better. However, the earlier benchmark on which we based the switch to
> age 0
> 
> (commit 0d8ff15e9a15f2b393e53337a107b7a1e5919b6d
> Author: Ben Widawsky <benjamin.widawsky@intel.com>
> Date:   Thu Jul 4 11:02:03 2013 -0700
> 
>     drm/i915/hsw: Set correct Haswell PTE encodings)
> 
> actually seems to prefer the default PTE encoding as age 3. Presumably,
> this is in part due to the use of MOCS to override the PTE encodings
> when appropriate.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=69870
> Tested-by: mengmeng.meng@intel.com
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_gem_gtt.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
> index efb5dab61c81..c4a3f9ae0d43 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> @@ -57,7 +57,9 @@ typedef gen8_gtt_pte_t gen8_ppgtt_pde_t;
>  #define HSW_WB_LLC_AGE3			HSW_CACHEABILITY_CONTROL(0x2)
>  #define HSW_WB_LLC_AGE0			HSW_CACHEABILITY_CONTROL(0x3)
>  #define HSW_WB_ELLC_LLC_AGE0		HSW_CACHEABILITY_CONTROL(0xb)
> +#define HSW_WB_ELLC_LLC_AGE3		HSW_CACHEABILITY_CONTROL(0x8)
>  #define HSW_WT_ELLC_LLC_AGE0		HSW_CACHEABILITY_CONTROL(0x6)
> +#define HSW_WT_ELLC_LLC_AGE3		HSW_CACHEABILITY_CONTROL(0x7)
>  
>  #define GEN8_PTES_PER_PAGE		(PAGE_SIZE / sizeof(gen8_gtt_pte_t))
>  #define GEN8_PDES_PER_PAGE		(PAGE_SIZE / sizeof(gen8_ppgtt_pde_t))
> @@ -185,10 +187,10 @@ static gen6_gtt_pte_t iris_pte_encode(dma_addr_t addr,
>  	case I915_CACHE_NONE:
>  		break;
>  	case I915_CACHE_WT:
> -		pte |= HSW_WT_ELLC_LLC_AGE0;
> +		pte |= HSW_WT_ELLC_LLC_AGE3;
>  		break;
>  	default:
> -		pte |= HSW_WB_ELLC_LLC_AGE0;
> +		pte |= HSW_WB_ELLC_LLC_AGE3;
>  		break;
>  	}
>  

Yeah I guess as long as userspace can override the default with MOCS,
this is fine.

Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
-- 
Jesse Barnes, Intel Open Source Technology Center