Re: [PATCH 4/4] drm/ttm: optimize ttm pool shrinker a bit

[Daniel Vetter <daniel@ffwll.ch>]

On Fri, Dec 18, 2020 at 06:55:38PM +0100, Christian König wrote:
> Only initialize the DMA coherent pools if they are used.
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>

Ah, just realized the answer to my question on patch 2: The pools are
per-device, due to dma_alloc_coherent being per-device (but really mostly
it isn't, but that's what we have to deal with fighting the dma-api
abstraction).

I think this would make a lot more sense if the shrinkers are per-pool
(and also most of the debugfs files), since as-is in a multi-gpu system
the first gpu's pool gets preferrentially thrashed. Which isn't a nice
design. Splitting that into per gpu shrinkers means we get equal shrinking
without having to maintain a global lru. This is how xfs seems to set up
their shrinkers, and in general xfs people have a solid understanding of
this stuff.

Aside: I think it also would make tons of sense to split up your new ttm
bo shrinker up into a per-device lru, and throw the global system memory
lru out the window completely :-) Assuming we can indeed get rid of it,
and vmwgfx doesn't need it somewhere still.

Aside from this lgtm, but I guess will change a bit with that shuffling.
-Daniel

> ---
>  drivers/gpu/drm/ttm/ttm_pool.c | 23 ++++++++++++++++-------
>  1 file changed, 16 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/ttm/ttm_pool.c b/drivers/gpu/drm/ttm/ttm_pool.c
> index 1cdacd58753a..f09e34614226 100644
> --- a/drivers/gpu/drm/ttm/ttm_pool.c
> +++ b/drivers/gpu/drm/ttm/ttm_pool.c
> @@ -504,10 +504,12 @@ void ttm_pool_init(struct ttm_pool *pool, struct device *dev,
>  	pool->use_dma_alloc = use_dma_alloc;
>  	pool->use_dma32 = use_dma32;
>  
> -	for (i = 0; i < TTM_NUM_CACHING_TYPES; ++i)
> -		for (j = 0; j < MAX_ORDER; ++j)
> -			ttm_pool_type_init(&pool->caching[i].orders[j],
> -					   pool, i, j);
> +	if (use_dma_alloc) {
> +		for (i = 0; i < TTM_NUM_CACHING_TYPES; ++i)
> +			for (j = 0; j < MAX_ORDER; ++j)
> +				ttm_pool_type_init(&pool->caching[i].orders[j],
> +						   pool, i, j);
> +	}
>  }
>  EXPORT_SYMBOL(ttm_pool_init);
>  
> @@ -523,9 +525,11 @@ void ttm_pool_fini(struct ttm_pool *pool)
>  {
>  	unsigned int i, j;
>  
> -	for (i = 0; i < TTM_NUM_CACHING_TYPES; ++i)
> -		for (j = 0; j < MAX_ORDER; ++j)
> -			ttm_pool_type_fini(&pool->caching[i].orders[j]);
> +	if (pool->use_dma_alloc) {
> +		for (i = 0; i < TTM_NUM_CACHING_TYPES; ++i)
> +			for (j = 0; j < MAX_ORDER; ++j)
> +				ttm_pool_type_fini(&pool->caching[i].orders[j]);
> +	}
>  }
>  EXPORT_SYMBOL(ttm_pool_fini);
>  
> @@ -630,6 +634,11 @@ int ttm_pool_debugfs(struct ttm_pool *pool, struct seq_file *m)
>  {
>  	unsigned int i;
>  
> +	if (!pool->use_dma_alloc) {
> +		seq_puts(m, "unused\n");
> +		return 0;
> +	}
> +
>  	ttm_pool_debugfs_header(m);
>  
>  	spin_lock(&shrinker_lock);
> -- 
> 2.25.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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