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

[Christian König]

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.koe...@amd.com>
---
  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