Re: [Intel-gfx] [PATCH] drm/i915: Do not sync RCU during shrinking

[Chris Wilson]

On Fri, May 05, 2017 at 12:40:09PM +0300, Joonas Lahtinen wrote:
> Due to the complex dependencies between workqueues and RCU, which
> are not easily detected by lockdep, do not synchronize RCU during
> shrinking. RCU sync gains us very little benefit in real life
> scenarios where the amount of memory used by object backing
> storage is dominant over the metadata under RCU.
> 
> Suggested-by: Chris Wilson 
> Signed-off-by: Joonas Lahtinen 
> Cc: Chris Wilson 
> Cc: Tvrtko Ursulin 
> Cc: J. R. Okajima 
> Cc: Andrea Arcangeli 
Reviewed-by: Chris Wilson 
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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[Intel-gfx] [PATCH] drm/i915: Do not sync RCU during shrinking

[Joonas Lahtinen]

Due to the complex dependencies between workqueues and RCU, which
are not easily detected by lockdep, do not synchronize RCU during
shrinking. RCU sync gains us very little benefit in real life
scenarios where the amount of memory used by object backing
storage is dominant over the metadata under RCU.

Suggested-by: Chris Wilson 
Signed-off-by: Joonas Lahtinen 
Cc: Chris Wilson 
Cc: Tvrtko Ursulin 
Cc: J. R. Okajima 
Cc: Andrea Arcangeli 
---
 drivers/gpu/drm/i915/i915_gem_shrinker.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_shrinker.c 
b/drivers/gpu/drm/i915/i915_gem_shrinker.c
index 0e7352d..e1868ed 100644
--- a/drivers/gpu/drm/i915/i915_gem_shrinker.c
+++ b/drivers/gpu/drm/i915/i915_gem_shrinker.c
@@ -59,9 +59,6 @@ static void shrinker_unlock(struct drm_i915_private 
*dev_priv, bool unlock)
return;
 
mutex_unlock(_priv->drm.struct_mutex);
-
-   /* expedite the RCU grace period to free some request slabs */
-   synchronize_rcu_expedited();
 }
 
 static bool any_vma_pinned(struct drm_i915_gem_object *obj)
-- 
2.7.4

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