From: chenying <[email protected]>
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. For this case,
we want to use trylock to reduce rq lock contention in load_balance().
We add rq->lb_lock for the load balancing path, and uses trylock to
try to acquire the busiest rq lb_lock, if it fails, clear the
busiest rq's cpu from load_balance_mask and then goto refind.
The test results show that this patch brings ~35% rq lock contentions
reduced and no scheduling latency reduction.
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: 24906 25996
0.08 27.77 43122.87 1.66
1216316 6601547 0.05 41.59 10224267.38
1.55
---------
&rq->lock 1210
[<000000000fe88813>] scheduler_tick+0x4f/0xf0
&rq->lock 1885
[<00000000de367e3c>] _nohz_idle_balance+0x116/0x250
&rq->lock 15111 [<00000000daf6fa95>]
update_blocked_averages+0x30/0x6f0
&rq->lock 1156
[<00000000d5c71b0e>] __schedule+0xa9/0x800
---------
&rq->lock 15542
[<00000000daf6fa95>] update_blocked_averages+0x30/0x6f0
&rq->lock 733
[<000000000fe88813>] scheduler_tick+0x4f/0xf0
&rq->lock 3066
[<000000000bc2ee47>] try_to_wake_up+0x206/0x710
&rq->lock 1272
[<00000000d5c71b0e>] __schedule+0xa9/0x800
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: 16174 17105
0.07 33.13 31154.45 1.82
1162817 6602803 0.05 64.68 10141979.28
1.54
---------
&rq->lock 11665
[<00000000ce27c902>] update_blocked_averages+0x30/0x700
&rq->lock 1457
[<00000000a6302c24>] try_to_wake_up+0x206/0x710
&rq->lock 1159
[<000000009f2bc605>] __schedule+0xa9/0x810
&rq->lock 1411
[<00000000aa0a6e31>] _nohz_idle_balance+0x116/0x250
---------
&rq->lock 3032
[<00000000a6302c24>] try_to_wake_up+0x206/0x710
&rq->lock 248
[<000000008bd7e827>] load_balance+0x571/0xe80
&rq->lock 11502
[<00000000ce27c902>] update_blocked_averages+0x30/0x700
&rq->lock 1253
[<000000009f2bc605>] __schedule+0xa9/0x810
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 |
|
test script:
#!/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 <[email protected]>
Signed-off-by: chenying <[email protected]>
---
kernel/sched/core.c | 1 +
kernel/sched/fair.c | 12 ++++++++++++
kernel/sched/sched.h | 1 +
3 files changed, 14 insertions(+)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index daff72f00385..d41f1a9c7d5f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -9697,6 +9697,7 @@ void __init sched_init(void)
rq = cpu_rq(i);
raw_spin_lock_init(&rq->__lock);
+ raw_spin_lock_init(&rq->lb_lock);
rq->nr_running = 0;
rq->calc_load_active = 0;
rq->calc_load_update = jiffies + LOAD_FREQ;
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e4a0b8bd941c..d92c42671b99 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 (!raw_spin_trylock(&busiest->lb_lock)) {
+ __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;
@@ -10403,6 +10412,8 @@ static int load_balance(int this_cpu, struct rq
*this_rq,
/* All tasks on this runqueue were pinned by CPU affinity */
if (unlikely(env.flags & LBF_ALL_PINNED)) {
+ raw_spin_unlock(&busiest->lb_lock);
+
__cpumask_clear_cpu(cpu_of(busiest), cpus);
/*
* Attempting to continue load balancing at the current
@@ -10420,6 +10431,7 @@ static int load_balance(int this_cpu, struct rq
*this_rq,
goto out_all_pinned;
}
}
+ raw_spin_unlock(&busiest->lb_lock);
if (!ld_moved) {
schedstat_inc(sd->lb_failed[idle]);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index a4a20046e586..384690bda8c3 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -954,6 +954,7 @@ struct balance_callback {
struct rq {
/* runqueue lock: */
raw_spinlock_t __lock;
+ raw_spinlock_t lb_lock;
/*
* nr_running and cpu_load should be in the same cacheline because
--
2.11.0
Hi Ying,
On 11/24/22 5:07 PM, chenying wrote:
> ...
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index a4a20046e586..384690bda8c3 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -954,6 +954,7 @@ struct balance_callback {
> struct rq {
> /* runqueue lock: */
> raw_spinlock_t __lock;
> + raw_spinlock_t lb_lock;
Do we really need a new lock for doing this? I may suggest the
following:
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 87522c3de7b2..30d84e066a9a 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1048,6 +1048,7 @@ struct rq {
struct balance_callback *balance_callback;
+ unsigned char balancing;
unsigned char nohz_idle_balance;
unsigned char idle_balance;
and skip in-balancing runqueues early when find_busiest_queue().
Thanks,
Abel
>
> /*
> * nr_running and cpu_load should be in the same cacheline because
From: chenying <[email protected]>
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 <[email protected]>
Signed-off-by: chenying <[email protected]>
---
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
On 2022-12-13 at 11:13:24 +0800, chenying wrote:
> From: chenying <[email protected]>
>
> 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
>
Does the scenario above indicate that one CPU is trying to grab the rq lock
in either __schedule or try_to_wake_up or update_blocked_averages or
_nohz_idle_balance.
but it could be grabbed by another CPU at load_balance+0x3b7/0xe40,
and this patch is trying to avoid grabbing the rq lock in load_balance()
as much as possible?
And it seems that update_blocked_averages is quite contended too.
> 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 &
>
May I know how many CPUs are there in the system, 46 * 2 ? So this test is
to saturate test1 and idle CPUs in test2 try to continously pull task from test1
but fail due to affinity, which introduce rq lock contention?
> Suggested-by: Abel Wu <[email protected]>
> Signed-off-by: chenying <[email protected]>
> ---
> 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;
Maybe rq->balancing = 0 because balancing is not bool.
> 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)) {
rq->balancing is not protected by lock so there could be race condition,
but I think it is ok because this could be a trade-off.
> + __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);
WRITE_ONCE(busiest->balancing, 1)
>
> /*
> * 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);
WRITE_ONCE(busiest->balancing, 0)
thanks,
Chenyu
在 2022/12/14 0:09, Chen Yu 写道:
> On 2022-12-13 at 11:13:24 +0800, chenying wrote:
>> From: chenying <[email protected]>
>>
>> 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
>>
> Does the scenario above indicate that one CPU is trying to grab the rq lock
> in either __schedule or try_to_wake_up or update_blocked_averages or
> _nohz_idle_balance.
> but it could be grabbed by another CPU at load_balance+0x3b7/0xe40,
> and this patch is trying to avoid grabbing the rq lock in load_balance()
> as much as possible?
> And it seems that update_blocked_averages is quite contended too.
Yes. This patch is mainly to reduce the meaningless lock waiting at
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 &
>>
> May I know how many CPUs are there in the system, 46 * 2 ? So this test is
> to saturate test1 and idle CPUs in test2 try to continously pull task from test1
> but fail due to affinity, which introduce rq lock contention?
Yes. This script is used to create an unbalanced scenario.
Architecture: x86_64
CPU op-mode(s): 32-bit, 64-bit
Byte Order: Little Endian
Address sizes: 46 bits physical, 48 bits virtual
CPU(s): 48
On-line CPU(s) list: 0-47
Thread(s) per core: 2
Core(s) per socket: 12
Socket(s): 2
NUMA node(s): 2
Vendor ID: GenuineIntel
CPU family: 6
Model: 79
Model name: Intel(R) Xeon(R) CPU E5-2650 v4 @ 2.20GHz
Stepping: 1
CPU MHz: 1202.860
CPU max MHz: 2900.0000
CPU min MHz: 1200.0000
BogoMIPS: 4400.16
Virtualization: VT-x
L1d cache: 32K
L1i cache: 32K
L2 cache: 256K
L3 cache: 30720K
NUMA node0 CPU(s):
0,2,4,6,8,10,12,14,16,18,20,22,24,26,28,30,32,34,36,38,40,42,44,46
NUMA node1 CPU(s):
1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31,33,35,37,39,41,43,45,47
>> Suggested-by: Abel Wu <[email protected]>
>> Signed-off-by: chenying <[email protected]>
>> ---
>> 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;
> Maybe rq->balancing = 0 because balancing is not bool.
>> 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)) {
> rq->balancing is not protected by lock so there could be race condition,
> but I think it is ok because this could be a trade-off.
>> + __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);
> WRITE_ONCE(busiest->balancing, 1)
>>
>> /*
>> * 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);
> WRITE_ONCE(busiest->balancing, 0)
>
> thanks,
> Chenyu
Hi Chen, thanks for reviewing!
On 12/14/22 12:09 AM, Chen Yu wrote:
> On 2022-12-13 at 11:13:24 +0800, chenying wrote:
>> From: chenying <[email protected]>
>>
>> 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
>>
> Does the scenario above indicate that one CPU is trying to grab the rq lock
> in either __schedule or try_to_wake_up or update_blocked_averages or
> _nohz_idle_balance.
> but it could be grabbed by another CPU at load_balance+0x3b7/0xe40,
> and this patch is trying to avoid grabbing the rq lock in load_balance()
> as much as possible?
Pretty much, and there can be other concern. The chosen busiest
cpu can be the src_cpu of multiple other cpus at same time, which
can lead to over pulling from the busiest cpu.
> And it seems that update_blocked_averages is quite contended too.
Yes indeed, since newidle_balance() is one of its callers.
>> 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 &
>>
> May I know how many CPUs are there in the system, 46 * 2 ? So this test is
> to saturate test1 and idle CPUs in test2 try to continously pull task from test1
> but fail due to affinity, which introduce rq lock contention?
Yeah seems so. Might be better to include some other benchmarks.
I think fast idling workload will benefit from this.
Best,
Abel
>> Suggested-by: Abel Wu <[email protected]>
>> Signed-off-by: chenying <[email protected]>
>> ---
>> 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;
> Maybe rq->balancing = 0 because balancing is not bool.
>> 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)) {
> rq->balancing is not protected by lock so there could be race condition,
> but I think it is ok because this could be a trade-off.
>> + __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);
> WRITE_ONCE(busiest->balancing, 1)
>>
>> /*
>> * 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);
> WRITE_ONCE(busiest->balancing, 0)
>
> thanks,
> Chenyu
On 12/13/22 11:13 AM, chenying wrote:
> [nit]
> 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;
> + }
> +
Here removing the cpu from @cpus will prevent it being selected once
a redo is triggered due to all tasks on the busiest cpu pinned by cpu
affinity. If that is the case, the removed cpu can still be the busiest
but not in balancing at that moment.
IMHO it'd be better skip the in-balancing cpus in find_busiest_queue()
without modifying @cpus to keep consistence among the redos.
Thanks & Best,
Abel