kernel/sched/fair.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)
newidle(CPU_NEWLY_IDLE) balancing doesn't stop the load balancing if the
continue_balancing flag is reset. Other two balancing (IDLE, BUSY) do
that. newidle balance stops the load balancing if rq has a task or there
is wakeup pending. The same checks are present in should_we_balance for
newidle. Hence use the return value and simplify continue_balancing
mechanism for newidle. Update the comment surrounding it as well.
No change in functionality intended.
Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
---
kernel/sched/fair.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f00cb66cc479..d80535df8f03 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -12307,6 +12307,7 @@ static int sched_balance_newidle(struct rq *this_rq, struct rq_flags *rf)
{
unsigned long next_balance = jiffies + HZ;
int this_cpu = this_rq->cpu;
+ int continue_balancing = 1;
u64 t0, t1, curr_cost = 0;
struct sched_domain *sd;
int pulled_task = 0;
@@ -12321,8 +12322,9 @@ static int sched_balance_newidle(struct rq *this_rq, struct rq_flags *rf)
return 0;
/*
- * We must set idle_stamp _before_ calling idle_balance(), such that we
- * measure the duration of idle_balance() as idle time.
+ * We must set idle_stamp _before_ calling sched_balance_rq()
+ * for CPU_NEWLY_IDLE, such that we measure the this duration
+ * as idle time.
*/
this_rq->idle_stamp = rq_clock(this_rq);
@@ -12361,7 +12363,6 @@ static int sched_balance_newidle(struct rq *this_rq, struct rq_flags *rf)
rcu_read_lock();
for_each_domain(this_cpu, sd) {
- int continue_balancing = 1;
u64 domain_cost;
update_next_balance(sd, &next_balance);
@@ -12387,8 +12388,7 @@ static int sched_balance_newidle(struct rq *this_rq, struct rq_flags *rf)
* Stop searching for tasks to pull if there are
* now runnable tasks on this rq.
*/
- if (pulled_task || this_rq->nr_running > 0 ||
- this_rq->ttwu_pending)
+ if (pulled_task || !continue_balancing)
break;
}
rcu_read_unlock();
--
2.39.3* Shrikanth Hegde <sshegde@linux.ibm.com> wrote: > newidle(CPU_NEWLY_IDLE) balancing doesn't stop the load balancing if the > continue_balancing flag is reset. Other two balancing (IDLE, BUSY) do > that. newidle balance stops the load balancing if rq has a task or there > is wakeup pending. The same checks are present in should_we_balance for > newidle. Hence use the return value and simplify continue_balancing > mechanism for newidle. Update the comment surrounding it as well. Assuming there are no side-effects to balancing behavior. > No change in functionality intended. Is this actually true? Any change to behavior invalidates such a sentence. > /* > + * We must set idle_stamp _before_ calling sched_balance_rq() > + * for CPU_NEWLY_IDLE, such that we measure the this duration > + * as idle time. > */ 'the this' ...? Thanks, Ingo
On 3/26/24 1:37 PM, Ingo Molnar wrote: > > * Shrikanth Hegde <sshegde@linux.ibm.com> wrote: > >> newidle(CPU_NEWLY_IDLE) balancing doesn't stop the load balancing if the >> continue_balancing flag is reset. Other two balancing (IDLE, BUSY) do >> that. newidle balance stops the load balancing if rq has a task or there >> is wakeup pending. The same checks are present in should_we_balance for >> newidle. Hence use the return value and simplify continue_balancing >> mechanism for newidle. Update the comment surrounding it as well. > > Assuming there are no side-effects to balancing behavior. I ran hackbench. More or less same results with patch. But thats very limited set of benchmarks. Let me do some more testing with it and send the results. > >> No change in functionality intended. > > Is this actually true? Any change to behavior invalidates such a sentence. From what i think, code path is same and I don't see any functionality changing. Correct me if i am wrong. Currently, sched_balance_newidle does the same check to bail out as the should_we_balance check in case of newidle. i.e should_we_balance if (env->dst_rq->nr_running > 0 || env->dst_rq->ttwu_pending) return 0; sched_balance_newidle if (pulled_task || this_rq->nr_running > 0 || this_rq->ttwu_pending) break; } > >> /* >> + * We must set idle_stamp _before_ calling sched_balance_rq() >> + * for CPU_NEWLY_IDLE, such that we measure the this duration >> + * as idle time. >> */ > > 'the this' ...? Sorry for the typo. it should be. "such that we measure this duration as idle time" > > Thanks, > > Ingo
On 26/03/2024 10:00, Shrikanth Hegde wrote:
>
> On 3/26/24 1:37 PM, Ingo Molnar wrote:
>>
>> * Shrikanth Hegde <sshegde@linux.ibm.com> wrote:
>>
[...]
>> Is this actually true? Any change to behavior invalidates such a sentence.
>
> From what i think, code path is same and I don't see any functionality changing.
> Correct me if i am wrong.
>
> Currently, sched_balance_newidle does the same check to bail out as the
> should_we_balance check in case of newidle. i.e
>
> should_we_balance
> if (env->dst_rq->nr_running > 0 || env->dst_rq->ttwu_pending)
> return 0;
>
> sched_balance_newidle
> if (pulled_task || this_rq->nr_running > 0 ||
> this_rq->ttwu_pending)
> break;
> }
LGTM. Commit 792b9f65a568 ("sched: Allow newidle balancing to bail out
of load_balance") (Jun 22) made sure that we leave sched_balance_rq()
(former load_balance()) for CPU_NEWLY_IDLE asap to reduce wakeup latency.
So IMHO, we can use 'continue_balancing' instead of 'this_rq->nr_running
> 0 || this_rq->ttwu_pending' in sched_balance_newidle() (former
newidle_balance()).
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
* Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:
> On 26/03/2024 10:00, Shrikanth Hegde wrote:
> >
> > On 3/26/24 1:37 PM, Ingo Molnar wrote:
> >>
> >> * Shrikanth Hegde <sshegde@linux.ibm.com> wrote:
> >>
>
> [...]
>
> >> Is this actually true? Any change to behavior invalidates such a sentence.
> >
> > From what i think, code path is same and I don't see any functionality changing.
> > Correct me if i am wrong.
> >
> > Currently, sched_balance_newidle does the same check to bail out as the
> > should_we_balance check in case of newidle. i.e
> >
> > should_we_balance
> > if (env->dst_rq->nr_running > 0 || env->dst_rq->ttwu_pending)
> > return 0;
> >
> > sched_balance_newidle
> > if (pulled_task || this_rq->nr_running > 0 ||
> > this_rq->ttwu_pending)
> > break;
> > }
>
> LGTM. Commit 792b9f65a568 ("sched: Allow newidle balancing to bail out
> of load_balance") (Jun 22) made sure that we leave sched_balance_rq()
> (former load_balance()) for CPU_NEWLY_IDLE asap to reduce wakeup latency.
>
> So IMHO, we can use 'continue_balancing' instead of 'this_rq->nr_running
> > 0 || this_rq->ttwu_pending' in sched_balance_newidle() (former
> newidle_balance()).
>
> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Thanks for the clarification, applied!
Ingo
The following commit has been merged into the sched/core branch of tip:
Commit-ID: c829d6818b60c591f70c060b2bb75d76cf0cec6d
Gitweb: https://git.kernel.org/tip/c829d6818b60c591f70c060b2bb75d76cf0cec6d
Author: Shrikanth Hegde <sshegde@linux.ibm.com>
AuthorDate: Mon, 25 Mar 2024 21:09:26 +05:30
Committer: Ingo Molnar <mingo@kernel.org>
CommitterDate: Tue, 26 Mar 2024 20:16:20 +01:00
sched/fair: Simplify the continue_balancing logic in sched_balance_newidle()
newidle(CPU_NEWLY_IDLE) balancing doesn't stop the load-balancing if the
continue_balancing flag is reset, but the other two balancing (IDLE, BUSY)
cases do that.
newidle balance stops the load balancing if rq has a task or there
is wakeup pending. The same checks are present in should_we_balance for
newidle. Hence use the return value and simplify continue_balancing
mechanism for newidle. Update the comment surrounding it as well.
No change in functionality intended.
Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://lore.kernel.org/r/20240325153926.274284-1-sshegde@linux.ibm.com
---
kernel/sched/fair.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 24a7530..1856e58 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -12358,6 +12358,7 @@ static int sched_balance_newidle(struct rq *this_rq, struct rq_flags *rf)
{
unsigned long next_balance = jiffies + HZ;
int this_cpu = this_rq->cpu;
+ int continue_balancing = 1;
u64 t0, t1, curr_cost = 0;
struct sched_domain *sd;
int pulled_task = 0;
@@ -12372,8 +12373,9 @@ static int sched_balance_newidle(struct rq *this_rq, struct rq_flags *rf)
return 0;
/*
- * We must set idle_stamp _before_ calling idle_balance(), such that we
- * measure the duration of idle_balance() as idle time.
+ * We must set idle_stamp _before_ calling sched_balance_rq()
+ * for CPU_NEWLY_IDLE, such that we measure the this duration
+ * as idle time.
*/
this_rq->idle_stamp = rq_clock(this_rq);
@@ -12412,7 +12414,6 @@ static int sched_balance_newidle(struct rq *this_rq, struct rq_flags *rf)
rcu_read_lock();
for_each_domain(this_cpu, sd) {
- int continue_balancing = 1;
u64 domain_cost;
update_next_balance(sd, &next_balance);
@@ -12438,8 +12439,7 @@ static int sched_balance_newidle(struct rq *this_rq, struct rq_flags *rf)
* Stop searching for tasks to pull if there are
* now runnable tasks on this rq.
*/
- if (pulled_task || this_rq->nr_running > 0 ||
- this_rq->ttwu_pending)
+ if (pulled_task || !continue_balancing)
break;
}
rcu_read_unlock();© 2016 - 2026 Red Hat, Inc.