[Beignet] [PATCH] Fix AUX buffer for really page aligned

[Guo, Yejun]

If the purpose is to be a note that the whole aux buf should be page aligned, I agree with it. Could you modify the code/comment  accordingly, thanks.

-----Original Message-----
From: Zhenyu Wang [mailto:zhenyuw at linux.intel.com] 
Sent: Thursday, October 23, 2014 10:36 AM
To: Guo, Yejun
Cc: beignet at lists.freedesktop.org
Subject: Re: [Beignet] [PATCH] Fix AUX buffer for really page aligned

On 2014.10.22 08:49:53 +0000, Guo, Yejun wrote:
> three comments in line, thanks.
> 

Thanks for review this.

>    gpgpu->aux_offset.surface_heap_offset = size_aux;
>    size_aux += sizeof(surface_heap_t);
>  
> @@ -784,7 +782,10 @@ intel_gpgpu_state_init(intel_gpgpu_t *gpgpu,
>    gpgpu->aux_offset.sampler_border_color_state_offset = size_aux;
>    size_aux += GEN_MAX_SAMPLERS * sizeof(gen7_sampler_border_color_t);
> 
> [Yejun] aux buffer contains several parts, each part has its own alignment requirement, so we can see several 'ALIGN'  in above code. The alignment is handled for each part, it is not feasible to move one/all of them to the last.
> 

The goal is to make sure final aux buffer size is page aligned after adding up all required aligned space size. My patch only counts on final size.

>  
> -  bo = dri_bo_alloc(gpgpu->drv->bufmgr, "AUX_BUFFER", size_aux, 0);
> +  //surface heap must be 4096 bytes aligned because state base 
> + address use 20bit for the address  size_aux = ALIGN(size_aux, 4096);
> +
> +  bo = dri_bo_alloc(gpgpu->drv->bufmgr, "AUX_BUFFER", size_aux, 
> + 4096);
> 
> [Yejun] the last parameter '4096' is to control the size of the whole buffer (to be page aligned), not to meet the align requirement of the base address, and it is not explicitly required and  is ignored in function drm_intel_gem_bo_alloc_internal. 
> 

It's for 'alignment' parameter. Yes current libdrm will optimize it as to be page aligned, but as your comment above it's a good note to say that we need aux buffer allocation to be page aligned, like for other objects, printf buf, timestamp, etc.

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