From: Rob Clark <[email protected]>
lock_stat + mmm_donut[1] say that this reduces contention on mm_lock
significantly (~350x lower waittime-max, and ~100x lower waittime-avg)
[1] https://chromium.googlesource.com/chromiumos/platform/microbenchmarks/+/refs/heads/main/mmm_donut.py
Signed-off-by: Rob Clark <[email protected]>
---
drivers/gpu/drm/msm/msm_drv.h | 3 +-
drivers/gpu/drm/msm/msm_gem.c | 2 +-
drivers/gpu/drm/msm/msm_gem_shrinker.c | 48 ++++++++++++++++++++++----
3 files changed, 45 insertions(+), 8 deletions(-)
diff --git a/drivers/gpu/drm/msm/msm_drv.h b/drivers/gpu/drm/msm/msm_drv.h
index c84e6f84cb6d..d8d64d34e6e3 100644
--- a/drivers/gpu/drm/msm/msm_drv.h
+++ b/drivers/gpu/drm/msm/msm_drv.h
@@ -184,7 +184,8 @@ struct msm_drm_private {
/**
* Lists of inactive GEM objects. Every bo is either in one of the
* inactive lists (depending on whether or not it is shrinkable) or
- * gpu->active_list (for the gpu it is active on[1])
+ * gpu->active_list (for the gpu it is active on[1]), or transiently
+ * on a temporary list as the shrinker is running.
*
* These lists are protected by mm_lock (which should be acquired
* before per GEM object lock). One should *not* hold mm_lock in
diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
index 2ecf7f1cef25..75cea5b801da 100644
--- a/drivers/gpu/drm/msm/msm_gem.c
+++ b/drivers/gpu/drm/msm/msm_gem.c
@@ -719,7 +719,7 @@ void msm_gem_purge(struct drm_gem_object *obj)
put_iova_vmas(obj);
msm_obj->madv = __MSM_MADV_PURGED;
- mark_unpurgable(msm_obj);
+ update_inactive(msm_obj);
drm_vma_node_unmap(&obj->vma_node, dev->anon_inode->i_mapping);
drm_gem_free_mmap_offset(obj);
diff --git a/drivers/gpu/drm/msm/msm_gem_shrinker.c b/drivers/gpu/drm/msm/msm_gem_shrinker.c
index f3e948af01c5..33a49641ef30 100644
--- a/drivers/gpu/drm/msm/msm_gem_shrinker.c
+++ b/drivers/gpu/drm/msm/msm_gem_shrinker.c
@@ -22,26 +22,62 @@ msm_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
{
struct msm_drm_private *priv =
container_of(shrinker, struct msm_drm_private, shrinker);
- struct msm_gem_object *msm_obj;
+ struct list_head still_in_list;
unsigned long freed = 0;
+ INIT_LIST_HEAD(&still_in_list);
+
mutex_lock(&priv->mm_lock);
- list_for_each_entry(msm_obj, &priv->inactive_dontneed, mm_list) {
- if (freed >= sc->nr_to_scan)
+ while (freed < sc->nr_to_scan) {
+ struct msm_gem_object *msm_obj = list_first_entry_or_null(
+ &priv->inactive_dontneed, typeof(*msm_obj), mm_list);
+
+ if (!msm_obj)
break;
- /* Use trylock, because we cannot block on a obj that
- * might be trying to acquire mm_lock
+
+ list_move_tail(&msm_obj->mm_list, &still_in_list);
+
+ /*
+ * If it is in the process of being freed, msm_gem_free_object
+ * can be blocked on mm_lock waiting to remove it. So just
+ * skip it.
*/
- if (!msm_gem_trylock(&msm_obj->base))
+ if (!kref_get_unless_zero(&msm_obj->base.refcount))
continue;
+
+ /*
+ * Now that we own a reference, we can drop mm_lock for the
+ * rest of the loop body, to reduce contention with the
+ * retire_submit path (which could make more objects purgable)
+ */
+
+ mutex_unlock(&priv->mm_lock);
+
+ /*
+ * Note that this still needs to be trylock, since we can
+ * hit shrinker in response to trying to get backing pages
+ * for this obj (ie. while it's lock is already held)
+ */
+ if (!msm_gem_trylock(&msm_obj->base))
+ goto tail;
+
if (is_purgeable(msm_obj)) {
+ /*
+ * This will move the obj out of still_in_list to
+ * the purged list
+ */
msm_gem_purge(&msm_obj->base);
freed += msm_obj->base.size >> PAGE_SHIFT;
}
msm_gem_unlock(&msm_obj->base);
+
+tail:
+ drm_gem_object_put(&msm_obj->base);
+ mutex_lock(&priv->mm_lock);
}
+ list_splice_tail(&still_in_list, &priv->inactive_dontneed);
mutex_unlock(&priv->mm_lock);
if (freed > 0) {
--
2.30.2
Hi,
On Fri, Apr 2, 2021 at 2:08 PM Rob Clark <[email protected]> wrote:
>
> From: Rob Clark <[email protected]>
>
> lock_stat + mmm_donut[1] say that this reduces contention on mm_lock
> significantly (~350x lower waittime-max, and ~100x lower waittime-avg)
>
> [1] https://chromium.googlesource.com/chromiumos/platform/microbenchmarks/+/refs/heads/main/mmm_donut.py
>
> Signed-off-by: Rob Clark <[email protected]>
> ---
> drivers/gpu/drm/msm/msm_drv.h | 3 +-
> drivers/gpu/drm/msm/msm_gem.c | 2 +-
> drivers/gpu/drm/msm/msm_gem_shrinker.c | 48 ++++++++++++++++++++++----
> 3 files changed, 45 insertions(+), 8 deletions(-)
Looks good to me now!
Reviewed-by: Douglas Anderson <[email protected]>