On 16/01/2018 15:12, Tvrtko Ursulin wrote:
On 16/01/2018 13:05, Chris Wilson wrote:
When we finally decide the gpu is idle, that is a good time to shrink
our kmem_caches.
v2: Comment upon the random sprinkling of rcu_barrier() inside the idle
worker.
Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursu...@linux.intel.com>
---
drivers/gpu/drm/i915/i915_gem.c | 30 ++++++++++++++++++++++++++++++
1 file changed, 30 insertions(+)
diff --git a/drivers/gpu/drm/i915/i915_gem.c
b/drivers/gpu/drm/i915/i915_gem.c
index 335731c93b4a..61b13fdfaa71 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -4716,6 +4716,21 @@ 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);
+}
+
static inline bool
new_requests_since_last_retire(const struct drm_i915_private *i915)
{
@@ -4803,6 +4818,21 @@ i915_gem_idle_work_handler(struct work_struct
*work)
GEM_BUG_ON(!dev_priv->gt.awake);
i915_queue_hangcheck(dev_priv);
}
+
+ /*
+ * We use magical TYPESAFE_BY_RCU kmem_caches whose pages are not
+ * returned to the system imediately but only after an RCU grace
+ * period. We want to encourage such pages to be returned and so
+ * incorporate a RCU barrier here to provide some rate limiting
+ * of the driver and flush the old pages before we free a new batch
+ * from the next round of shrinking.
+ */
+ rcu_barrier();
Should this go into the conditional below? I don't think it makes a
difference effectively, but may be more logical.
+
+ if (!new_requests_since_last_retire(dev_priv)) {
+ __i915_gem_free_work(&dev_priv->mm.free_work);
I thought for a bit if re-using the worker from here is completely fine
but I think it is. We expect only one pass when called from here so
need_resched will be correctly neutralized/not-relevant from this path.
Hm, unless if we consider mmap_gtt users.. so we could still have new
objects appearing on the free_list after the 1st pass. And then
need_resched might kick us out. What do you think?
This also ties back to what I wrote in the earlier reply - do we want to
shrink the obj and vma caches from here? It may be colliding with
mmap_gtt operations. But it sounds appealing to tidy them, and I can't
think of any other convenient point. Given how we are de-prioritising
mmap_gtt its probably fine.
Regards,
Tvrtko
+ shrink_caches(dev_priv);
+ }
}
int i915_gem_suspend(struct drm_i915_private *dev_priv)
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