[PATCH v3 1/1] rcu/kvfree: Update KFREE_DRAIN_JIFFIES interval
From: Uladzislau Rezki (Sony)
Date: Wed Jun 01 2022 - 05:28:53 EST
Currently the monitor work is scheduled with a fixed interval of HZ/20,
which is roughly 50 milliseconds. The drawback of this approach is
low utilization of the 512 page slots in scenarios with infrequence
kvfree_rcu() calls. For example on an Android system:
<snip>
kworker/3:3-507 [003] .... 470.286305: rcu_invoke_kfree_bulk_callback: rcu_preempt bulk=0x00000000d0f0dde5 nr_records=6
kworker/6:1-76 [006] .... 470.416613: rcu_invoke_kfree_bulk_callback: rcu_preempt bulk=0x00000000ea0d6556 nr_records=1
kworker/6:1-76 [006] .... 470.416625: rcu_invoke_kfree_bulk_callback: rcu_preempt bulk=0x000000003e025849 nr_records=9
kworker/1:1-73 [001] .... 470.438895: rcu_invoke_kfree_bulk_callback: rcu_preempt bulk=0x0000000091a38dc1 nr_records=1
kworker/3:3-507 [003] .... 471.390000: rcu_invoke_kfree_bulk_callback: rcu_preempt bulk=0x00000000815a8713 nr_records=48
kworker/1:1-73 [001] .... 471.725785: rcu_invoke_kfree_bulk_callback: rcu_preempt bulk=0x00000000fda9bf20 nr_records=3
kworker/1:1-73 [001] .... 471.725833: rcu_invoke_kfree_bulk_callback: rcu_preempt bulk=0x00000000a425b67b nr_records=76
kworker/3:3-507 [003] .... 471.958960: rcu_invoke_kfree_bulk_callback: rcu_preempt bulk=0x00000000dce5bdbd nr_records=78
kworker/0:4-1411 [000] .... 472.085673: rcu_invoke_kfree_bulk_callback: rcu_preempt bulk=0x000000007996be9d nr_records=1
kworker/0:4-1411 [000] .... 472.085728: rcu_invoke_kfree_bulk_callback: rcu_preempt bulk=0x00000000d0f0dde5 nr_records=5
kworker/6:1-76 [006] .... 472.260340: rcu_invoke_kfree_bulk_callback: rcu_preempt bulk=0x0000000065630ee4 nr_records=102
kworker/2:1-78 [002] .... 472.527362: rcu_invoke_kfree_bulk_callback: rcu_preempt bulk=0x00000000815a8713 nr_records=1
<snip>
Out of 512 slots, in all cases, fewer than 10 were actually used.
In order to improve batching and make utilization more efficient this
commit sets a drain interval to a fixed 1-second interval. Floods are
detected when a page fills quickly, and in that case, the reclaim work
is re-scheduled for the next scheduling-clock tick (jiffy).
After this change:
<snip>
kworker/0:5-1415 [000] .... 239.852727: rcu_invoke_kfree_bulk_callback: rcu_preempt bulk=0x000000005d2561ea nr_records=178
kworker/3:0-38 [003] .... 239.855113: rcu_invoke_kfree_bulk_callback: rcu_preempt bulk=0x0000000039c44d27 nr_records=93
kworker/1:4-1747 [001] .... 239.872647: rcu_invoke_kfree_bulk_callback: rcu_preempt bulk=0x000000004abb2f7e nr_records=109
kworker/4:59-288 [004] .... 239.884829: rcu_invoke_kfree_bulk_callback: rcu_preempt bulk=0x0000000049e7a308 nr_records=182
kworker/0:5-1415 [000] .... 240.028762: rcu_invoke_kfree_bulk_callback: rcu_preempt bulk=0x0000000037eae6d6 nr_records=86
kworker/3:0-38 [003] .... 240.040769: rcu_invoke_kfree_bulk_callback: rcu_preempt bulk=0x000000003be0ae55 nr_records=244
kworker/3:0-38 [003] .... 240.068639: rcu_invoke_kfree_bulk_callback: rcu_preempt bulk=0x0000000021905efe nr_records=45
<...>-1415 [000] .... 240.868830: rcu_invoke_kfree_bulk_callback: rcu_preempt bulk=0x000000007c97e065 nr_records=461
<...>-1415 [000] .... 241.068646: rcu_invoke_kfree_bulk_callback: rcu_preempt bulk=0x000000000725886e nr_records=25
kworker/0:5-1415 [000] .... 241.100931: rcu_invoke_kfree_bulk_callback: rcu_preempt bulk=0x0000000021905efe nr_records=300
worker/4:59-2880 [004] .... 241.801181: rcu_invoke_kfree_bulk_callback: rcu_preempt bulk=0x000000004abb2f7e nr_records=180
worker/6:60-2554 [006] .... 242.000565: rcu_invoke_kfree_bulk_callback: rcu_preempt bulk=0x000000006d3084af nr_records=40
<snip>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
---
kernel/rcu/tree.c | 27 +++++++++++++++++++++++----
1 file changed, 23 insertions(+), 4 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index fd16c0b46d9e..37f89bedf45e 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3249,7 +3249,7 @@ EXPORT_SYMBOL_GPL(call_rcu);
/* Maximum number of jiffies to wait before draining a batch. */
-#define KFREE_DRAIN_JIFFIES (HZ / 50)
+#define KFREE_DRAIN_JIFFIES (HZ)
#define KFREE_N_BATCHES 2
#define FREE_N_CHANNELS 2
@@ -3510,6 +3510,25 @@ need_offload_krc(struct kfree_rcu_cpu *krcp)
return !!krcp->head;
}
+static void
+schedule_delayed_monitor_work(struct kfree_rcu_cpu *krcp)
+{
+ long delay, delay_left;
+
+ delay = READ_ONCE(krcp->count) >= KVFREE_BULK_MAX_ENTR ? 1:KFREE_DRAIN_JIFFIES;
+
+ if (delayed_work_pending(&krcp->monitor_work)) {
+ delay_left = krcp->monitor_work.timer.expires - jiffies;
+
+ if (delay < delay_left)
+ mod_delayed_work(system_wq, &krcp->monitor_work, delay);
+
+ return;
+ }
+
+ queue_delayed_work(system_wq, &krcp->monitor_work, delay);
+}
+
/*
* This function is invoked after the KFREE_DRAIN_JIFFIES timeout.
*/
@@ -3567,7 +3586,7 @@ static void kfree_rcu_monitor(struct work_struct *work)
// work to repeat an attempt. Because previous batches are
// still in progress.
if (need_offload_krc(krcp))
- schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES);
+ schedule_delayed_monitor_work(krcp);
raw_spin_unlock_irqrestore(&krcp->lock, flags);
}
@@ -3755,7 +3774,7 @@ void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
// Set timer to drain after KFREE_DRAIN_JIFFIES.
if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING)
- schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES);
+ schedule_delayed_monitor_work(krcp);
unlock_return:
krc_this_cpu_unlock(krcp, flags);
@@ -3831,7 +3850,7 @@ void __init kfree_rcu_scheduler_running(void)
raw_spin_lock_irqsave(&krcp->lock, flags);
if (need_offload_krc(krcp))
- schedule_delayed_work_on(cpu, &krcp->monitor_work, KFREE_DRAIN_JIFFIES);
+ schedule_delayed_monitor_work(krcp);
raw_spin_unlock_irqrestore(&krcp->lock, flags);
}
}
--
2.30.2