Re: [PATCH 04/12] drm/ttm: add common accounting to the resource mgr

[Christian König <ckoenig.leichtzumerken@xxxxxxxxx>]

Am 31.08.21 um 14:52 schrieb Daniel Vetter:
> On Mon, Aug 30, 2021 at 10:56:59AM +0200, Christian König wrote:
> > It makes sense to have this in the common manager for debugging and
> > accounting of how much resources are used.
> >
> > Signed-off-by: Christian König <christian.koenig@xxxxxxx>
> > ---
> >   drivers/gpu/drm/ttm/ttm_resource.c |  8 ++++++++
> >   include/drm/ttm/ttm_resource.h     | 18 ++++++++++++++++++
> >   2 files changed, 26 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/ttm/ttm_resource.c b/drivers/gpu/drm/ttm/ttm_resource.c
> > index a4c495da0040..426e6841fc89 100644
> > --- a/drivers/gpu/drm/ttm/ttm_resource.c
> > +++ b/drivers/gpu/drm/ttm/ttm_resource.c
> > @@ -33,6 +33,8 @@ void ttm_resource_init(struct ttm_buffer_object *bo,
> >                          const struct ttm_place *place,
> >                          struct ttm_resource *res)
> >   {
> > +	struct ttm_resource_manager *man;
> > +
> >   	res->start = 0;
> >   	res->num_pages = PFN_UP(bo->base.size);
> >   	res->mem_type = place->mem_type;
> > @@ -42,12 +44,16 @@ void ttm_resource_init(struct ttm_buffer_object *bo,
> >   	res->bus.is_iomem = false;
> >   	res->bus.caching = ttm_cached;
> >   	res->bo = bo;
> > +
> > +	man = ttm_manager_type(bo->bdev, place->mem_type);
> > +	atomic64_add(bo->base.size, &man->usage);
> >   }
> >   EXPORT_SYMBOL(ttm_resource_init);
> >   
> >   void ttm_resource_fini(struct ttm_resource_manager *man,
> >   		       struct ttm_resource *res)
> >   {
> > +	atomic64_sub(res->bo->base.size, &man->usage);
> >   }
> >   EXPORT_SYMBOL(ttm_resource_fini);
> >   
> > @@ -100,6 +106,7 @@ void ttm_resource_manager_init(struct ttm_resource_manager *man,
> >   	spin_lock_init(&man->move_lock);
> >   	man->bdev = bdev;
> >   	man->size = p_size;
> > +	atomic64_set(&man->usage, 0);
> >   
> >   	for (i = 0; i < TTM_MAX_BO_PRIORITY; ++i)
> >   		INIT_LIST_HEAD(&man->lru[i]);
> > @@ -172,6 +179,7 @@ void ttm_resource_manager_debug(struct ttm_resource_manager *man,
> >   	drm_printf(p, "  use_type: %d\n", man->use_type);
> >   	drm_printf(p, "  use_tt: %d\n", man->use_tt);
> >   	drm_printf(p, "  size: %llu\n", man->size);
> > +	drm_printf(p, "  usage: %llu\n", atomic64_read(&man->usage));
> >   	if (man->func->debug)
> >   		man->func->debug(man, p);
> >   }
> > diff --git a/include/drm/ttm/ttm_resource.h b/include/drm/ttm/ttm_resource.h
> > index e8080192cae4..526fe359c603 100644
> > --- a/include/drm/ttm/ttm_resource.h
> > +++ b/include/drm/ttm/ttm_resource.h
> > @@ -27,6 +27,7 @@
> >   
> >   #include <linux/types.h>
> >   #include <linux/mutex.h>
> > +#include <linux/atomic.h>
> >   #include <linux/dma-buf-map.h>
> >   #include <linux/dma-fence.h>
> >   #include <drm/drm_print.h>
> > @@ -110,6 +111,7 @@ struct ttm_resource_manager_func {
> >    * static information. bdev::driver::io_mem_free is never used.
> >    * @lru: The lru list for this memory type.
> >    * @move: The fence of the last pipelined move operation.
> > + * @usage: How much of the region is used.
> >    *
> >    * This structure is used to identify and manage memory types for a device.
> >    */
> > @@ -134,6 +136,9 @@ struct ttm_resource_manager {
> >   	 * Protected by @move_lock.
> >   	 */
> >   	struct dma_fence *move;
> > +
> > +	/* Own protection */
> > +	atomic64_t usage;
> Shouldn't we keep track of this together with the lru updates, under the
> same spinlock?

Mhm, what should that be good for? As far as I know we use it for two 
use cases:
1. Early abort when size-usage < requested.
2. Statistics for debugging.

Especially the first use case is rather important under memory pressure 
to avoid costly acquiring of a contended lock.

> Otherwise this usage here just becomes kinda meaningless I think, and just
> for some debugging. I really don't like sprinkling random atomic_t around
> (mostly because i915-gem code has gone totally overboard with them, with
> complete disregard to complexity of the result).

Well this here just replaces what drivers did anyway and the cost of 
inc/dec an atomic is pretty much negligible.

Christian.

> -Daniel
>
> >   };
> >   
> >   /**
> > @@ -260,6 +265,19 @@ ttm_resource_manager_cleanup(struct ttm_resource_manager *man)
> >   	man->move = NULL;
> >   }
> >   
> > +/**
> > + * ttm_resource_manager_usage
> > + *
> > + * @man: A memory manager object.
> > + *
> > + * Return how many resources are currently used.
> > + */
> > +static inline uint64_t
> > +ttm_resource_manager_usage(struct ttm_resource_manager *man)
> > +{
> > +	return atomic64_read(&man->usage);
> > +}
> > +
> >   void ttm_resource_init(struct ttm_buffer_object *bo,
> >                          const struct ttm_place *place,
> >                          struct ttm_resource *res);
> > --
> > 2.25.1