On 18/12/2019 12:57, Chris Wilson wrote:
Quoting Tvrtko Ursulin (2019-12-18 12:49:26)
On 18/12/2019 09:40, Chris Wilson wrote:
When doing our global park, we like to be a good citizen and shrink our
slab caches (of which we have quite a few now), but each
kmem_cache_shrink() incurs a stop_machine() and so ends up being quite
expensive, causing machine-wide stalls. While ideally we would like to
throw away unused pages in our slab caches whenever it appears that we
are idling, doing so will require a much cheaper mechanism. In the
meantime use a delayed worked to impose a rate-limit that means we have
to have been idle for more than 2 seconds before we start shrinking.
I was thinking about this yesterday, while looking at rapid park-unpark
cycles!
References: https://gitlab.freedesktop.org/drm/intel/issues/848
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
---
drivers/gpu/drm/i915/i915_globals.c | 53 ++++++++++++++++++++++++-----
1 file changed, 44 insertions(+), 9 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_globals.c b/drivers/gpu/drm/i915/i915_globals.c
index be127cd28931..3aa213684293 100644
--- a/drivers/gpu/drm/i915/i915_globals.c
+++ b/drivers/gpu/drm/i915/i915_globals.c
@@ -20,7 +20,10 @@ static LIST_HEAD(globals);
static atomic_t active;
static atomic_t epoch;
static struct park_work {
- struct rcu_work work;
+ struct delayed_work work;
+ struct rcu_head rcu;
+ unsigned long flags;
+#define PENDING 0
int epoch;
} park;
@@ -37,11 +40,33 @@ static void i915_globals_shrink(void)
global->shrink();
}
+static void __i915_globals_grace(struct rcu_head *rcu)
+{
+ /* Ratelimit parking as shrinking is quite slow */
+ schedule_delayed_work(&park.work, round_jiffies_up_relative(2 * HZ));
+}
+
+static void __i915_globals_queue_rcu(void)
+{
+ park.epoch = atomic_inc_return(&epoch);
+ if (!atomic_read(&active)) {
+ init_rcu_head(&park.rcu);
Do we need to do init/destroy more than once? I think once on driver
load/exit would be more correct since the head is statically allocated.
I did on each fresh invocation to have a better chance of detecting
wrong lifetimes. Because the first patch did call call_rcu() while
still active, I thought by having the debugobject init it would give us
the early warning that it was still alive. Similarly by calling
destroy_rcu as we transition to the delayed_work should catch if we
happen to be still active on rcu lists.
That was all I was thinking, it would give us better debug information.
Double init emits a warning? Okay, that works as well then.
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Regards,
Tvrtko
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