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drm/i915: Ratelimit i915_globals_park 

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.

References: https://gitlab.freedesktop.org/drm/intel/issues/848
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191218094057.3510459-1-chris@chris-wilson.co.uk
This commit is contained in:
Chris Wilson 2019-12-18 09:40:57 +00:00
parent 54400257ae
commit 01f624f018
1 changed files with 44 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

53
drivers/gpu/drm/i915/i915_globals.c
View File

@ -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);
call_rcu(&park.rcu, __i915_globals_grace);
}
}
static void __i915_globals_park(struct work_struct *work)
{
destroy_rcu_head(&park.rcu);
/* Confirm nothing woke up in the last grace period */
if (park.epoch == atomic_read(&epoch))
i915_globals_shrink();
if (park.epoch != atomic_read(&epoch)) {
__i915_globals_queue_rcu();
return;
}
clear_bit(PENDING, &park.flags);
i915_globals_shrink();
}
void __init i915_global_register(struct i915_global *global)
@ -85,7 +110,7 @@ int __init i915_globals_init(void)
}
}
INIT_RCU_WORK(&park.work, __i915_globals_park);
INIT_DELAYED_WORK(&park.work, __i915_globals_park);
return 0;
}
@ -103,8 +128,9 @@ void i915_globals_park(void)
if (!atomic_dec_and_test(&active))
return;
park.epoch = atomic_inc_return(&epoch);
queue_rcu_work(system_wq, &park.work);
/* Queue cleanup after the next RCU grace period has freed slabs */
if (!test_and_set_bit(PENDING, &park.flags))
__i915_globals_queue_rcu();
}
void i915_globals_unpark(void)
@ -113,12 +139,21 @@ void i915_globals_unpark(void)
atomic_inc(&active);
}
static void __exit __i915_globals_flush(void)
{
atomic_inc(&active); /* skip shrinking */
rcu_barrier(); /* wait for the work to be queued */
flush_delayed_work(&park.work);
atomic_dec(&active);
}
void __exit i915_globals_exit(void)
{
/* Flush any residual park_work */
atomic_inc(&epoch);
flush_rcu_work(&park.work);
GEM_BUG_ON(atomic_read(&active));
__i915_globals_flush();
__i915_globals_cleanup();
/* And ensure that our DESTROY_BY_RCU slabs are truly destroyed */