On 24/01/2018 11:03, Chris Wilson wrote:
When we finally decide the gpu is idle, that is a good time to shrink
our kmem_caches.
v3: Defer until an rcu grace period after we idle.
v4: Think about epoch wraparound and how likely that is.
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
---
drivers/gpu/drm/i915/i915_gem.c | 78 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 78 insertions(+)
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 7f0684ccc724..60b34bb98ee3 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -3334,6 +3334,65 @@ i915_gem_retire_work_handler(struct work_struct *work)
}
}
+static void shrink_caches(struct drm_i915_private *i915)
+{
+ /*
+ * kmem_cache_shrink() discards empty slabs and reorders partially
+ * filled slabs to prioritise allocating from the mostly full slabs,
+ * with the aim of reducing fragmentation.
+ */
+ kmem_cache_shrink(i915->priorities);
+ kmem_cache_shrink(i915->dependencies);
+ kmem_cache_shrink(i915->requests);
+ kmem_cache_shrink(i915->luts);
+ kmem_cache_shrink(i915->vmas);
+ kmem_cache_shrink(i915->objects);
+}
+
+struct sleep_rcu_work {
+ union {
+ struct rcu_head rcu;
+ struct work_struct work;
+ };
+ struct drm_i915_private *i915;
+ unsigned int epoch;
+};
+
+static inline bool
+same_epoch(struct drm_i915_private *i915, unsigned int epoch)
+{
+ /*
+ * There is a small chance that the epoch wrapped since we started
+ * sleeping. If we assume that epoch is at least a u32, then it will
+ * take at least 2^32 * 100ms for it to wrap, or about 326 years.
+ */
+ return epoch == READ_ONCE(i915->gt.epoch);
+}
+
+static void __sleep_work(struct work_struct *work)
+{
+ struct sleep_rcu_work *s = container_of(work, typeof(*s), work);
+ struct drm_i915_private *i915 = s->i915;
+ unsigned int epoch = s->epoch;
+
+ kfree(s);
+ if (same_epoch(i915, epoch))
+ shrink_caches(i915);
+}
+
+static void __sleep_rcu(struct rcu_head *rcu)
+{
+ struct sleep_rcu_work *s = container_of(rcu, typeof(*s), rcu);
+ struct drm_i915_private *i915 = s->i915;
+
+ if (same_epoch(i915, s->epoch)) {
+ INIT_WORK(&s->work, __sleep_work);
+ queue_work(i915->wq, &s->work);
+ } else {
+ kfree(s);
+ }
+}
+
static inline bool
new_requests_since_last_retire(const struct drm_i915_private *i915)
{
@@ -3346,6 +3405,7 @@ i915_gem_idle_work_handler(struct work_struct *work)
{
struct drm_i915_private *dev_priv =
container_of(work, typeof(*dev_priv), gt.idle_work.work);
+ unsigned int epoch = 0;
bool rearm_hangcheck;
ktime_t end;
@@ -3406,6 +3466,7 @@ i915_gem_idle_work_handler(struct work_struct *work)
GEM_BUG_ON(!dev_priv->gt.awake);
dev_priv->gt.awake = false;
rearm_hangcheck = false;
+ epoch = dev_priv->gt.epoch;
if (INTEL_GEN(dev_priv) >= 6)
gen6_rps_idle(dev_priv);
@@ -3421,6 +3482,23 @@ i915_gem_idle_work_handler(struct work_struct *work)
GEM_BUG_ON(!dev_priv->gt.awake);
i915_queue_hangcheck(dev_priv);
}
+
+ /*
+ * When we are idle, it is an opportune time to reap our caches.
+ * However, we have many objects that utilise RCU and the ordered
+ * i915->wq that this work is executing on. To try and flush any
+ * pending frees now we are idle, we first wait for an RCU grace
+ * period, and then queue a task (that will run last on the wq) to
+ * shrink and re-optimize the caches.
+ */
+ if (same_epoch(dev_priv, epoch)) {
+ struct sleep_rcu_work *s = kmalloc(sizeof(*s), GFP_KERNEL);
+ if (s) {
+ s->i915 = dev_priv;
+ s->epoch = epoch;
+ call_rcu(&s->rcu, __sleep_rcu);
+ }
+ }
}
void i915_gem_close_object(struct drm_gem_object *gem, struct drm_file *file)
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Regards,
Tvrtko
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