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| author | Chris Wilson <chris@chris-wilson.co.uk> | 2018-01-15 20:57:59 +0000 |
|---|---|---|
| committer | Chris Wilson <chris@chris-wilson.co.uk> | 2018-01-16 10:47:39 +0000 |
| commit | 2ef1e729c7f0fbad9706848f5fe5cff84f5b6d24 (patch) | |
| tree | 65e1bc8867a0821ab28388bbf046db3b9c04025d /drivers/gpu/drm/i915/i915_gem.c | |
| parent | 2aa472c8279a0eea4649283fd1266cb629b8a5d3 (diff) | |
| download | talos-obmc-linux-2ef1e729c7f0fbad9706848f5fe5cff84f5b6d24.tar.gz talos-obmc-linux-2ef1e729c7f0fbad9706848f5fe5cff84f5b6d24.zip | |
drm/i915: Rewrite some comments around RCU-deferred object free
Tvrtko noticed that the comments describing the interaction of RCU and
the deferred worker for freeing drm_i915_gem_object were a little
confusing, so attempt to bring some sense to them.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180115205759.13884-1-chris@chris-wilson.co.uk
Diffstat (limited to 'drivers/gpu/drm/i915/i915_gem.c')
| -rw-r--r-- | drivers/gpu/drm/i915/i915_gem.c | 19 |
1 files changed, 13 insertions, 6 deletions
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index 87937c4f9dff..b2ba685cb144 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -4699,7 +4699,8 @@ static void __i915_gem_free_work(struct work_struct *work) container_of(work, struct drm_i915_private, mm.free_work); struct llist_node *freed; - /* All file-owned VMA should have been released by this point through + /* + * All file-owned VMA should have been released by this point through * i915_gem_close_object(), or earlier by i915_gem_context_close(). * However, the object may also be bound into the global GTT (e.g. * older GPUs without per-process support, or for direct access through @@ -4726,10 +4727,15 @@ static void __i915_gem_free_object_rcu(struct rcu_head *head) container_of(head, typeof(*obj), rcu); struct drm_i915_private *i915 = to_i915(obj->base.dev); - /* We can't simply use call_rcu() from i915_gem_free_object() - * as we need to block whilst unbinding, and the call_rcu - * task may be called from softirq context. So we take a - * detour through a worker. + /* + * Since we require blocking on struct_mutex to unbind the freed + * object from the GPU before releasing resources back to the + * system, we can not do that directly from the RCU callback (which may + * be a softirq context), but must instead then defer that work onto a + * kthread. We use the RCU callback rather than move the freed object + * directly onto the work queue so that we can mix between using the + * worker and performing frees directly from subsequent allocations for + * crude but effective memory throttling. */ if (llist_add(&obj->freed, &i915->mm.free_list)) queue_work(i915->wq, &i915->mm.free_work); @@ -4745,7 +4751,8 @@ void i915_gem_free_object(struct drm_gem_object *gem_obj) if (discard_backing_storage(obj)) obj->mm.madv = I915_MADV_DONTNEED; - /* Before we free the object, make sure any pure RCU-only + /* + * Before we free the object, make sure any pure RCU-only * read-side critical sections are complete, e.g. * i915_gem_busy_ioctl(). For the corresponding synchronized * lookup see i915_gem_object_lookup_rcu(). |
