Messages in this thread Patch in this message | | | Date | Tue, 13 Dec 2022 11:13:24 +0800 | Subject | [PATCH] sched: Reduce rq lock contention in load_balance() | From | chenying <> |
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From: chenying <chenying.kernel@bytedance.com>
When doing newidle load balancing, we may have lock contention on rq->lock while finding the same busiest rq on multiple cpus. However, it is often the case that after the first load balancing, the busiest-rq may not be the busiest anymore. This may lead to pointless waits for locks.
Add rq->balancing to quickly check if the busiest rq has been selected in load_balance on other cpu. If it has been selected, clear the busiest rq's cpu from load_balance_mask and then goto refind.
The test results show that this patch brings ~30% rq lock contentions reduced and no scheduling latency degradation.
unpatched: lock_stat version 0.4 ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- class name con-bounces contentions waittime-min waittime-max waittime-total waittime-avg acq-bounces acquisitions holdtime-min holdtime-max holdtime-total holdtime-avg -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
&rq->lock: 25532 26471 0.09 22.86 42250.81 1.60 1232063 6586225 0.05 40.54 10280028.19 1.56 --------- &rq->lock 1310 [<0000000081600630>] __schedule+0xa9/0x800 &rq->lock 1430 [<00000000754f510d>] try_to_wake_up+0x206/0x710 &rq->lock 15426 [<0000000020af4cb5>] update_blocked_averages+0x30/0x6f0 &rq->lock 1449 [<00000000dc949053>] _nohz_idle_balance+0x116/0x250 --------- &rq->lock 3329 [<00000000754f510d>] try_to_wake_up+0x206/0x710 &rq->lock 1241 [<0000000081600630>] __schedule+0xa9/0x800 &rq->lock 15480 [<0000000020af4cb5>] update_blocked_averages+0x30/0x6f0 &rq->lock 5333 [<000000004969102f>] load_balance+0x3b7/0xe40
patched: lock_stat version 0.4 ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- class name con-bounces contentions waittime-min waittime-max waittime-total waittime-avg acq-bounces acquisitions holdtime-min holdtime-max holdtime-total holdtime-avg .............................................................................................................................................................................................................................
&rq->lock: 17497 18300 0.09 23.15 32152.22 1.76 1137409 6484176 0.05 40.19 10125220.60 1.56 --------- &rq->lock 12298 [<000000004314e22f>] update_blocked_averages+0x30/0x6f0 &rq->lock 1005 [<000000005b222b90>] __schedule+0xa9/0x800 &rq->lock 1271 [<00000000c7a66a89>] try_to_wake_up+0x206/0x710 &rq->lock 1380 [<00000000eac23b6b>] load_balance+0x560/0xe70 --------- &rq->lock 2962 [<00000000c7a66a89>] try_to_wake_up+0x206/0x710 &rq->lock 11844 [<000000004314e22f>] update_blocked_averages+0x30/0x6f0 &rq->lock 592 [<0000000032421516>] scheduler_tick+0x4f/0xf0 &rq->lock 1243 [<000000005b222b90>] __schedule+0xa9/0x800
unpatched: # ./runqlat 60 1
usecs : count distribution 0 -> 1 : 1172 | | 2 -> 3 : 210063 |************************ | 4 -> 7 : 337576 |****************************************| 8 -> 15 : 24555 |** | 16 -> 31 : 13598 |* | 32 -> 63 : 779 | | 64 -> 127 : 230 | | 128 -> 255 : 83 | | 256 -> 511 : 54 | | 512 -> 1023 : 62 | | 1024 -> 2047 : 123 | | 2048 -> 4095 : 283 | | 4096 -> 8191 : 1362 | | 8192 -> 16383 : 2775 | | 16384 -> 32767 : 52352 |****** | 32768 -> 65535 : 14 | | 65536 -> 131071 : 140 | |
patched: # ./runqlat 60 1
usecs : count distribution 0 -> 1 : 1091 | | 2 -> 3 : 205259 |*********************** | 4 -> 7 : 351620 |****************************************| 8 -> 15 : 27812 |*** | 16 -> 31 : 13971 |* | 32 -> 63 : 727 | | 64 -> 127 : 198 | | 128 -> 255 : 103 | | 256 -> 511 : 61 | | 512 -> 1023 : 45 | | 1024 -> 2047 : 108 | | 2048 -> 4095 : 271 | | 4096 -> 8191 : 1342 | | 8192 -> 16383 : 2732 | | 16384 -> 32767 : 49367 |***** | 32768 -> 65535 : 8 | | 65536 -> 131071 : 183 | |
Below is the script to run the sysbench workload:
#!/bin/bash
mkdir /sys/fs/cgroup/cpuset/test1 echo 12,14,16,18,20,22 > /sys/fs/cgroup/cpuset/test1/cpuset.cpus echo 0 > /sys/fs/cgroup/cpuset/test1/cpuset.mems
mkdir /sys/fs/cgroup/cpuset/test2 echo 0,2,4,6,8,10,12,14,16,18,20,22,24,26,28,30,32,34,36,38,40,42,44,46 > /sys/fs/cgroup/cpuset/test2/cpuset.cpus echo 0 > /sys/fs/cgroup/cpuset/test2/cpuset.mems
cgexec -g cpuset:test1 sysbench --test=cpu --cpu-max-prime=200000 run --num-threads=24 --rate=100 --time=6000 & cgexec -g cpuset:test2 sysbench --test=cpu --cpu-max-prime=200000 run --num-threads=96 --rate=100 --time=6000 &
Suggested-by: Abel Wu <wuyun.abel@bytedance.com> Signed-off-by: chenying <chenying.kernel@bytedance.com> --- kernel/sched/core.c | 1 + kernel/sched/fair.c | 11 +++++++++++ kernel/sched/sched.h | 1 + 3 files changed, 13 insertions(+)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index daff72f00385..ca4fa84c8751 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -9737,6 +9737,7 @@ void __init sched_init(void) rq->rd = NULL; rq->cpu_capacity = rq->cpu_capacity_orig = SCHED_CAPACITY_SCALE; rq->balance_callback = &balance_push_callback; + rq->balancing = false; rq->active_balance = 0; rq->next_balance = jiffies; rq->push_cpu = 0; diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index e4a0b8bd941c..aeb4fa9ac93a 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -10295,6 +10295,7 @@ static int load_balance(int this_cpu, struct rq *this_rq, goto out_balanced; }
+refind: busiest = find_busiest_queue(&env, group); if (!busiest) { schedstat_inc(sd->lb_nobusyq[idle]); @@ -10303,6 +10304,14 @@ static int load_balance(int this_cpu, struct rq *this_rq,
WARN_ON_ONCE(busiest == env.dst_rq);
+ if (READ_ONCE(busiest->balancing)) { + __cpumask_clear_cpu(cpu_of(busiest), cpus); + if (cpumask_intersects(sched_group_span(group), cpus)) + goto refind; + + goto out_balanced; + } + schedstat_add(sd->lb_imbalance[idle], env.imbalance);
env.src_cpu = busiest->cpu; @@ -10323,6 +10332,7 @@ static int load_balance(int this_cpu, struct rq *this_rq, more_balance: rq_lock_irqsave(busiest, &rf); update_rq_clock(busiest); + WRITE_ONCE(busiest->balancing, true);
/* * cur_ld_moved - load moved in current iteration @@ -10338,6 +10348,7 @@ static int load_balance(int this_cpu, struct rq *this_rq, * See task_rq_lock() family for the details. */
+ WRITE_ONCE(busiest->balancing, false); rq_unlock(busiest, &rf);
if (cur_ld_moved) { diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index a4a20046e586..6730808a0ab8 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1044,6 +1044,7 @@ struct rq {
struct balance_callback *balance_callback;
+ unsigned char balancing; unsigned char nohz_idle_balance; unsigned char idle_balance;
-- 2.11.0
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