* [PATCH 1/4] sched/fair: Remove SIS_AVG_CPU
2021-01-27 13:51 [PATCH v5 0/4] Scan for an idle sibling in a single pass Mel Gorman
@ 2021-01-27 13:52 ` Mel Gorman
2021-01-27 13:52 ` [PATCH 2/4] sched/fair: Move avg_scan_cost calculations under SIS_PROP Mel Gorman
` (3 subsequent siblings)
4 siblings, 0 replies; 10+ messages in thread
From: Mel Gorman @ 2021-01-27 13:52 UTC (permalink / raw)
To: Peter Zijlstra, Ingo Molnar
Cc: Vincent Guittot, Li Aubrey, Qais Yousef, LKML, Mel Gorman
SIS_AVG_CPU was introduced as a means of avoiding a search when the
average search cost indicated that the search would likely fail. It was
a blunt instrument and disabled by commit 4c77b18cf8b7 ("sched/fair: Make
select_idle_cpu() more aggressive") and later replaced with a proportional
search depth by commit 1ad3aaf3fcd2 ("sched/core: Implement new approach
to scale select_idle_cpu()").
While there are corner cases where SIS_AVG_CPU is better, it has now been
disabled for almost three years. As the intent of SIS_PROP is to reduce
the time complexity of select_idle_cpu(), lets drop SIS_AVG_CPU and focus
on SIS_PROP as a throttling mechanism.
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
---
kernel/sched/fair.c | 20 +++++++++-----------
kernel/sched/features.h | 1 -
2 files changed, 9 insertions(+), 12 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 04a3ce20da67..9f5682aeda2e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6145,7 +6145,6 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
{
struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask);
struct sched_domain *this_sd;
- u64 avg_cost, avg_idle;
u64 time;
int this = smp_processor_id();
int cpu, nr = INT_MAX;
@@ -6154,18 +6153,17 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
if (!this_sd)
return -1;
- /*
- * Due to large variance we need a large fuzz factor; hackbench in
- * particularly is sensitive here.
- */
- avg_idle = this_rq()->avg_idle / 512;
- avg_cost = this_sd->avg_scan_cost + 1;
+ if (sched_feat(SIS_PROP)) {
+ u64 avg_cost, avg_idle, span_avg;
- if (sched_feat(SIS_AVG_CPU) && avg_idle < avg_cost)
- return -1;
+ /*
+ * Due to large variance we need a large fuzz factor;
+ * hackbench in particularly is sensitive here.
+ */
+ avg_idle = this_rq()->avg_idle / 512;
+ avg_cost = this_sd->avg_scan_cost + 1;
- if (sched_feat(SIS_PROP)) {
- u64 span_avg = sd->span_weight * avg_idle;
+ span_avg = sd->span_weight * avg_idle;
if (span_avg > 4*avg_cost)
nr = div_u64(span_avg, avg_cost);
else
diff --git a/kernel/sched/features.h b/kernel/sched/features.h
index 68d369cba9e4..e875eabb6600 100644
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -54,7 +54,6 @@ SCHED_FEAT(TTWU_QUEUE, true)
/*
* When doing wakeups, attempt to limit superfluous scans of the LLC domain.
*/
-SCHED_FEAT(SIS_AVG_CPU, false)
SCHED_FEAT(SIS_PROP, true)
/*
--
2.26.2
^ permalink raw reply related [flat|nested] 10+ messages in thread
* [PATCH 2/4] sched/fair: Move avg_scan_cost calculations under SIS_PROP
2021-01-27 13:51 [PATCH v5 0/4] Scan for an idle sibling in a single pass Mel Gorman
2021-01-27 13:52 ` [PATCH 1/4] sched/fair: Remove SIS_AVG_CPU Mel Gorman
@ 2021-01-27 13:52 ` Mel Gorman
2021-01-27 13:52 ` [PATCH 3/4] sched/fair: Remove select_idle_smt() Mel Gorman
` (2 subsequent siblings)
4 siblings, 0 replies; 10+ messages in thread
From: Mel Gorman @ 2021-01-27 13:52 UTC (permalink / raw)
To: Peter Zijlstra, Ingo Molnar
Cc: Vincent Guittot, Li Aubrey, Qais Yousef, LKML, Mel Gorman
As noted by Vincent Guittot, avg_scan_costs are calculated for SIS_PROP
even if SIS_PROP is disabled. Move the time calculations under a SIS_PROP
check and while we are at it, exclude the cost of initialising the CPU
mask from the average scan cost.
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
---
kernel/sched/fair.c | 14 ++++++++------
1 file changed, 8 insertions(+), 6 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9f5682aeda2e..c8d8e185cf3b 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6153,6 +6153,8 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
if (!this_sd)
return -1;
+ cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
+
if (sched_feat(SIS_PROP)) {
u64 avg_cost, avg_idle, span_avg;
@@ -6168,11 +6170,9 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
nr = div_u64(span_avg, avg_cost);
else
nr = 4;
- }
-
- time = cpu_clock(this);
- cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
+ time = cpu_clock(this);
+ }
for_each_cpu_wrap(cpu, cpus, target) {
if (!--nr)
@@ -6181,8 +6181,10 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
break;
}
- time = cpu_clock(this) - time;
- update_avg(&this_sd->avg_scan_cost, time);
+ if (sched_feat(SIS_PROP)) {
+ time = cpu_clock(this) - time;
+ update_avg(&this_sd->avg_scan_cost, time);
+ }
return cpu;
}
--
2.26.2
^ permalink raw reply related [flat|nested] 10+ messages in thread
* [PATCH 3/4] sched/fair: Remove select_idle_smt()
2021-01-27 13:51 [PATCH v5 0/4] Scan for an idle sibling in a single pass Mel Gorman
2021-01-27 13:52 ` [PATCH 1/4] sched/fair: Remove SIS_AVG_CPU Mel Gorman
2021-01-27 13:52 ` [PATCH 2/4] sched/fair: Move avg_scan_cost calculations under SIS_PROP Mel Gorman
@ 2021-01-27 13:52 ` Mel Gorman
2021-01-27 13:52 ` [PATCH 4/4] sched/fair: Merge select_idle_core/cpu() Mel Gorman
2021-02-01 1:13 ` [PATCH v5 0/4] Scan for an idle sibling in a single pass Li, Aubrey
4 siblings, 0 replies; 10+ messages in thread
From: Mel Gorman @ 2021-01-27 13:52 UTC (permalink / raw)
To: Peter Zijlstra, Ingo Molnar
Cc: Vincent Guittot, Li Aubrey, Qais Yousef, LKML, Mel Gorman
From: Peter Zijlstra (Intel) <peterz@infradead.org>
In order to make the next patch more readable, and to quantify the
actual effectiveness of this pass, start by removing it.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
---
kernel/sched/fair.c | 30 ------------------------------
1 file changed, 30 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c8d8e185cf3b..fe587350ea14 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6101,27 +6101,6 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int
return -1;
}
-/*
- * Scan the local SMT mask for idle CPUs.
- */
-static int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target)
-{
- int cpu;
-
- if (!static_branch_likely(&sched_smt_present))
- return -1;
-
- for_each_cpu(cpu, cpu_smt_mask(target)) {
- if (!cpumask_test_cpu(cpu, p->cpus_ptr) ||
- !cpumask_test_cpu(cpu, sched_domain_span(sd)))
- continue;
- if (available_idle_cpu(cpu) || sched_idle_cpu(cpu))
- return cpu;
- }
-
- return -1;
-}
-
#else /* CONFIG_SCHED_SMT */
static inline int select_idle_core(struct task_struct *p, struct sched_domain *sd, int target)
@@ -6129,11 +6108,6 @@ static inline int select_idle_core(struct task_struct *p, struct sched_domain *s
return -1;
}
-static inline int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target)
-{
- return -1;
-}
-
#endif /* CONFIG_SCHED_SMT */
/*
@@ -6323,10 +6297,6 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
if ((unsigned)i < nr_cpumask_bits)
return i;
- i = select_idle_smt(p, sd, target);
- if ((unsigned)i < nr_cpumask_bits)
- return i;
-
return target;
}
--
2.26.2
^ permalink raw reply related [flat|nested] 10+ messages in thread
* [PATCH 4/4] sched/fair: Merge select_idle_core/cpu()
2021-01-27 13:51 [PATCH v5 0/4] Scan for an idle sibling in a single pass Mel Gorman
` (2 preceding siblings ...)
2021-01-27 13:52 ` [PATCH 3/4] sched/fair: Remove select_idle_smt() Mel Gorman
@ 2021-01-27 13:52 ` Mel Gorman
2021-02-17 13:17 ` [tip: sched/core] " tip-bot2 for Mel Gorman
2021-02-01 1:13 ` [PATCH v5 0/4] Scan for an idle sibling in a single pass Li, Aubrey
4 siblings, 1 reply; 10+ messages in thread
From: Mel Gorman @ 2021-01-27 13:52 UTC (permalink / raw)
To: Peter Zijlstra, Ingo Molnar
Cc: Vincent Guittot, Li Aubrey, Qais Yousef, LKML, Mel Gorman
From: Peter Zijlstra (Intel) <peterz@infradead.org>
Both select_idle_core() and select_idle_cpu() do a loop over the same
cpumask. Observe that by clearing the already visited CPUs, we can
fold the iteration and iterate a core at a time.
All we need to do is remember any non-idle CPU we encountered while
scanning for an idle core. This way we'll only iterate every CPU once.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
---
kernel/sched/fair.c | 99 +++++++++++++++++++++++++++------------------
1 file changed, 59 insertions(+), 40 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index fe587350ea14..01591e24a95f 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6006,6 +6006,14 @@ static inline int find_idlest_cpu(struct sched_domain *sd, struct task_struct *p
return new_cpu;
}
+static inline int __select_idle_cpu(int cpu)
+{
+ if (available_idle_cpu(cpu) || sched_idle_cpu(cpu))
+ return cpu;
+
+ return -1;
+}
+
#ifdef CONFIG_SCHED_SMT
DEFINE_STATIC_KEY_FALSE(sched_smt_present);
EXPORT_SYMBOL_GPL(sched_smt_present);
@@ -6064,48 +6072,51 @@ void __update_idle_core(struct rq *rq)
* there are no idle cores left in the system; tracked through
* sd_llc->shared->has_idle_cores and enabled through update_idle_core() above.
*/
-static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int target)
+static int select_idle_core(struct task_struct *p, int core, struct cpumask *cpus, int *idle_cpu)
{
- struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask);
- int core, cpu;
+ bool idle = true;
+ int cpu;
if (!static_branch_likely(&sched_smt_present))
- return -1;
-
- if (!test_idle_cores(target, false))
- return -1;
-
- cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
+ return __select_idle_cpu(core);
- for_each_cpu_wrap(core, cpus, target) {
- bool idle = true;
-
- for_each_cpu(cpu, cpu_smt_mask(core)) {
- if (!available_idle_cpu(cpu)) {
- idle = false;
- break;
+ for_each_cpu(cpu, cpu_smt_mask(core)) {
+ if (!available_idle_cpu(cpu)) {
+ idle = false;
+ if (*idle_cpu == -1) {
+ if (sched_idle_cpu(cpu) && cpumask_test_cpu(cpu, p->cpus_ptr)) {
+ *idle_cpu = cpu;
+ break;
+ }
+ continue;
}
+ break;
}
-
- if (idle)
- return core;
-
- cpumask_andnot(cpus, cpus, cpu_smt_mask(core));
+ if (*idle_cpu == -1 && cpumask_test_cpu(cpu, p->cpus_ptr))
+ *idle_cpu = cpu;
}
- /*
- * Failed to find an idle core; stop looking for one.
- */
- set_idle_cores(target, 0);
+ if (idle)
+ return core;
+ cpumask_andnot(cpus, cpus, cpu_smt_mask(core));
return -1;
}
#else /* CONFIG_SCHED_SMT */
-static inline int select_idle_core(struct task_struct *p, struct sched_domain *sd, int target)
+static inline void set_idle_cores(int cpu, int val)
{
- return -1;
+}
+
+static inline bool test_idle_cores(int cpu, bool def)
+{
+ return def;
+}
+
+static inline int select_idle_core(struct task_struct *p, int core, struct cpumask *cpus, int *idle_cpu)
+{
+ return __select_idle_cpu(core);
}
#endif /* CONFIG_SCHED_SMT */
@@ -6118,10 +6129,11 @@ static inline int select_idle_core(struct task_struct *p, struct sched_domain *s
static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int target)
{
struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask);
+ int i, cpu, idle_cpu = -1, nr = INT_MAX;
+ bool smt = test_idle_cores(target, false);
+ int this = smp_processor_id();
struct sched_domain *this_sd;
u64 time;
- int this = smp_processor_id();
- int cpu, nr = INT_MAX;
this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc));
if (!this_sd)
@@ -6129,7 +6141,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
- if (sched_feat(SIS_PROP)) {
+ if (sched_feat(SIS_PROP) && !smt) {
u64 avg_cost, avg_idle, span_avg;
/*
@@ -6149,18 +6161,29 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
}
for_each_cpu_wrap(cpu, cpus, target) {
- if (!--nr)
- return -1;
- if (available_idle_cpu(cpu) || sched_idle_cpu(cpu))
- break;
+ if (smt) {
+ i = select_idle_core(p, cpu, cpus, &idle_cpu);
+ if ((unsigned int)i < nr_cpumask_bits)
+ return i;
+
+ } else {
+ if (!--nr)
+ return -1;
+ idle_cpu = __select_idle_cpu(cpu);
+ if ((unsigned int)idle_cpu < nr_cpumask_bits)
+ break;
+ }
}
- if (sched_feat(SIS_PROP)) {
+ if (smt)
+ set_idle_cores(this, false);
+
+ if (sched_feat(SIS_PROP) && !smt) {
time = cpu_clock(this) - time;
update_avg(&this_sd->avg_scan_cost, time);
}
- return cpu;
+ return idle_cpu;
}
/*
@@ -6289,10 +6312,6 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
if (!sd)
return target;
- i = select_idle_core(p, sd, target);
- if ((unsigned)i < nr_cpumask_bits)
- return i;
-
i = select_idle_cpu(p, sd, target);
if ((unsigned)i < nr_cpumask_bits)
return i;
--
2.26.2
^ permalink raw reply related [flat|nested] 10+ messages in thread
* [tip: sched/core] sched/fair: Merge select_idle_core/cpu()
2021-01-27 13:52 ` [PATCH 4/4] sched/fair: Merge select_idle_core/cpu() Mel Gorman
@ 2021-02-17 13:17 ` tip-bot2 for Mel Gorman
0 siblings, 0 replies; 10+ messages in thread
From: tip-bot2 for Mel Gorman @ 2021-02-17 13:17 UTC (permalink / raw)
To: linux-tip-commits
Cc: Mel Gorman, Peter Zijlstra (Intel),
Ingo Molnar, Vincent Guittot, x86, linux-kernel
The following commit has been merged into the sched/core branch of tip:
Commit-ID: 9fe1f127b913318c631d0041ecf71486e38c2c2d
Gitweb: https://git.kernel.org/tip/9fe1f127b913318c631d0041ecf71486e38c2c2d
Author: Mel Gorman <mgorman@techsingularity.net>
AuthorDate: Wed, 27 Jan 2021 13:52:03
Committer: Ingo Molnar <mingo@kernel.org>
CommitterDate: Wed, 17 Feb 2021 14:07:25 +01:00
sched/fair: Merge select_idle_core/cpu()
Both select_idle_core() and select_idle_cpu() do a loop over the same
cpumask. Observe that by clearing the already visited CPUs, we can
fold the iteration and iterate a core at a time.
All we need to do is remember any non-idle CPU we encountered while
scanning for an idle core. This way we'll only iterate every CPU once.
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lkml.kernel.org/r/20210127135203.19633-5-mgorman@techsingularity.net
---
kernel/sched/fair.c | 99 +++++++++++++++++++++++++------------------
1 file changed, 59 insertions(+), 40 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6a0fc8a..c73d588 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6019,6 +6019,14 @@ static inline int find_idlest_cpu(struct sched_domain *sd, struct task_struct *p
return new_cpu;
}
+static inline int __select_idle_cpu(int cpu)
+{
+ if (available_idle_cpu(cpu) || sched_idle_cpu(cpu))
+ return cpu;
+
+ return -1;
+}
+
#ifdef CONFIG_SCHED_SMT
DEFINE_STATIC_KEY_FALSE(sched_smt_present);
EXPORT_SYMBOL_GPL(sched_smt_present);
@@ -6077,48 +6085,51 @@ unlock:
* there are no idle cores left in the system; tracked through
* sd_llc->shared->has_idle_cores and enabled through update_idle_core() above.
*/
-static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int target)
+static int select_idle_core(struct task_struct *p, int core, struct cpumask *cpus, int *idle_cpu)
{
- struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask);
- int core, cpu;
+ bool idle = true;
+ int cpu;
if (!static_branch_likely(&sched_smt_present))
- return -1;
-
- if (!test_idle_cores(target, false))
- return -1;
-
- cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
+ return __select_idle_cpu(core);
- for_each_cpu_wrap(core, cpus, target) {
- bool idle = true;
-
- for_each_cpu(cpu, cpu_smt_mask(core)) {
- if (!available_idle_cpu(cpu)) {
- idle = false;
- break;
+ for_each_cpu(cpu, cpu_smt_mask(core)) {
+ if (!available_idle_cpu(cpu)) {
+ idle = false;
+ if (*idle_cpu == -1) {
+ if (sched_idle_cpu(cpu) && cpumask_test_cpu(cpu, p->cpus_ptr)) {
+ *idle_cpu = cpu;
+ break;
+ }
+ continue;
}
+ break;
}
-
- if (idle)
- return core;
-
- cpumask_andnot(cpus, cpus, cpu_smt_mask(core));
+ if (*idle_cpu == -1 && cpumask_test_cpu(cpu, p->cpus_ptr))
+ *idle_cpu = cpu;
}
- /*
- * Failed to find an idle core; stop looking for one.
- */
- set_idle_cores(target, 0);
+ if (idle)
+ return core;
+ cpumask_andnot(cpus, cpus, cpu_smt_mask(core));
return -1;
}
#else /* CONFIG_SCHED_SMT */
-static inline int select_idle_core(struct task_struct *p, struct sched_domain *sd, int target)
+static inline void set_idle_cores(int cpu, int val)
{
- return -1;
+}
+
+static inline bool test_idle_cores(int cpu, bool def)
+{
+ return def;
+}
+
+static inline int select_idle_core(struct task_struct *p, int core, struct cpumask *cpus, int *idle_cpu)
+{
+ return __select_idle_cpu(core);
}
#endif /* CONFIG_SCHED_SMT */
@@ -6131,10 +6142,11 @@ static inline int select_idle_core(struct task_struct *p, struct sched_domain *s
static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int target)
{
struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask);
+ int i, cpu, idle_cpu = -1, nr = INT_MAX;
+ bool smt = test_idle_cores(target, false);
+ int this = smp_processor_id();
struct sched_domain *this_sd;
u64 time;
- int this = smp_processor_id();
- int cpu, nr = INT_MAX;
this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc));
if (!this_sd)
@@ -6142,7 +6154,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
- if (sched_feat(SIS_PROP)) {
+ if (sched_feat(SIS_PROP) && !smt) {
u64 avg_cost, avg_idle, span_avg;
/*
@@ -6162,18 +6174,29 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
}
for_each_cpu_wrap(cpu, cpus, target) {
- if (!--nr)
- return -1;
- if (available_idle_cpu(cpu) || sched_idle_cpu(cpu))
- break;
+ if (smt) {
+ i = select_idle_core(p, cpu, cpus, &idle_cpu);
+ if ((unsigned int)i < nr_cpumask_bits)
+ return i;
+
+ } else {
+ if (!--nr)
+ return -1;
+ idle_cpu = __select_idle_cpu(cpu);
+ if ((unsigned int)idle_cpu < nr_cpumask_bits)
+ break;
+ }
}
- if (sched_feat(SIS_PROP)) {
+ if (smt)
+ set_idle_cores(this, false);
+
+ if (sched_feat(SIS_PROP) && !smt) {
time = cpu_clock(this) - time;
update_avg(&this_sd->avg_scan_cost, time);
}
- return cpu;
+ return idle_cpu;
}
/*
@@ -6302,10 +6325,6 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
if (!sd)
return target;
- i = select_idle_core(p, sd, target);
- if ((unsigned)i < nr_cpumask_bits)
- return i;
-
i = select_idle_cpu(p, sd, target);
if ((unsigned)i < nr_cpumask_bits)
return i;
^ permalink raw reply related [flat|nested] 10+ messages in thread
* Re: [PATCH v5 0/4] Scan for an idle sibling in a single pass
2021-01-27 13:51 [PATCH v5 0/4] Scan for an idle sibling in a single pass Mel Gorman
` (3 preceding siblings ...)
2021-01-27 13:52 ` [PATCH 4/4] sched/fair: Merge select_idle_core/cpu() Mel Gorman
@ 2021-02-01 1:13 ` Li, Aubrey
2021-02-01 13:06 ` Mel Gorman
4 siblings, 1 reply; 10+ messages in thread
From: Li, Aubrey @ 2021-02-01 1:13 UTC (permalink / raw)
To: Mel Gorman, Peter Zijlstra, Ingo Molnar
Cc: Vincent Guittot, Qais Yousef, LKML
On 2021/1/27 21:51, Mel Gorman wrote:
> Changelog since v4
> o Avoid use of intermediate variable during select_idle_cpu
>
> Changelog since v3
> o Drop scanning based on cores, SMT4 results showed problems
>
> Changelog since v2
> o Remove unnecessary parameters
> o Update nr during scan only when scanning for cpus
>
> Changlog since v1
> o Move extern declaration to header for coding style
> o Remove unnecessary parameter from __select_idle_cpu
>
> This series of 4 patches reposts three patches from Peter entitled
> "select_idle_sibling() wreckage". It only scans the runqueues in a single
> pass when searching for an idle sibling.
>
> Three patches from Peter were dropped. The first patch altered how scan
> depth was calculated. Scan depth deletion is a random number generator
> with two major limitations. The avg_idle time is based on the time
> between a CPU going idle and being woken up clamped approximately by
> 2*sysctl_sched_migration_cost. This is difficult to compare in a sensible
> fashion to avg_scan_cost. The second issue is that only the avg_scan_cost
> of scan failures is recorded and it does not decay. This requires deeper
> surgery that would justify a patch on its own although Peter notes that
> https://lkml.kernel.org/r/20180530143105.977759909@infradead.org is
> potentially useful for an alternative avg_idle metric.
>
> The second patch dropped scanned based on cores instead of CPUs as it
> rationalised the difference between core scanning and CPU scanning.
> Unfortunately, Vincent reported problems with SMT4 so it's dropped
> for now until depth searching can be fixed.
>
> The third patch dropped converted the idle core scan throttling mechanism
> to SIS_PROP. While this would unify the throttling of core and CPU
> scanning, it was not free of regressions and has_idle_cores is a fairly
> effective throttling mechanism with the caveat that it can have a lot of
> false positives for workloads like hackbench.
>
> Peter's series tried to solve three problems at once, this subset addresses
> one problem.
>
> kernel/sched/fair.c | 151 +++++++++++++++++++---------------------
> kernel/sched/features.h | 1 -
> 2 files changed, 70 insertions(+), 82 deletions(-)
>
4 benchmarks measured on a x86 4s system with 24 cores per socket and
2 HTs per core, total 192 CPUs.
The load level is [25%, 50%, 75%, 100%].
- hackbench almost has a universal win.
- netperf high load has notable changes, as well as tbench 50% load.
Details below:
hackbench: 10 iterations, 10000 loops, 40 fds per group
======================================================
- pipe process
group base %std v5 %std
3 1 19.18 1.0266 9.06
6 1 9.17 0.987 13.03
9 1 7.11 1.0195 4.61
12 1 1.07 0.9927 1.43
- pipe thread
group base %std v5 %std
3 1 11.14 0.9742 7.27
6 1 9.15 0.9572 7.48
9 1 2.95 0.986 4.05
12 1 1.75 0.9992 1.68
- socket process
group base %std v5 %std
3 1 2.9 0.9586 2.39
6 1 0.68 0.9641 1.3
9 1 0.64 0.9388 0.76
12 1 0.56 0.9375 0.55
- socket thread
group base %std v5 %std
3 1 3.82 0.9686 2.97
6 1 2.06 0.9667 1.91
9 1 0.44 0.9354 1.25
12 1 0.54 0.9362 0.6
netperf: 10 iterations x 100 seconds, transactions rate / sec
=============================================================
- tcp request/response performance
thread base %std v4 %std
25% 1 5.34 1.0039 5.13
50% 1 4.97 1.0115 6.3
75% 1 5.09 0.9257 6.75
100% 1 4.53 0.908 4.83
- udp request/response performance
thread base %std v4 %std
25% 1 6.18 0.9896 6.09
50% 1 5.88 1.0198 8.92
75% 1 24.38 0.9236 29.14
100% 1 26.16 0.9063 22.16
tbench: 10 iterations x 100 seconds, throughput / sec
=====================================================
thread base %std v4 %std
25% 1 0.45 1.003 1.48
50% 1 1.71 0.9286 0.82
75% 1 0.84 0.9928 0.94
100% 1 0.76 0.9762 0.59
schbench: 10 iterations x 100 seconds, 99th percentile latency
==============================================================
mthread base %std v4 %std
25% 1 2.89 0.9884 7.34
50% 1 40.38 1.0055 38.37
75% 1 4.76 1.0095 4.62
100% 1 10.09 1.0083 8.03
Thanks,
-Aubrey
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH v5 0/4] Scan for an idle sibling in a single pass
2021-02-01 1:13 ` [PATCH v5 0/4] Scan for an idle sibling in a single pass Li, Aubrey
@ 2021-02-01 13:06 ` Mel Gorman
0 siblings, 0 replies; 10+ messages in thread
From: Mel Gorman @ 2021-02-01 13:06 UTC (permalink / raw)
To: Li, Aubrey
Cc: Peter Zijlstra, Ingo Molnar, Vincent Guittot, Qais Yousef, LKML
On Mon, Feb 01, 2021 at 09:13:16AM +0800, Li, Aubrey wrote:
> > Peter's series tried to solve three problems at once, this subset addresses
> > one problem.
> >
> > kernel/sched/fair.c | 151 +++++++++++++++++++---------------------
> > kernel/sched/features.h | 1 -
> > 2 files changed, 70 insertions(+), 82 deletions(-)
> >
>
> 4 benchmarks measured on a x86 4s system with 24 cores per socket and
> 2 HTs per core, total 192 CPUs.
>
> The load level is [25%, 50%, 75%, 100%].
>
> - hackbench almost has a universal win.
> - netperf high load has notable changes, as well as tbench 50% load.
>
Ok, both netperf and tbench are somewhat expected as at those loads are
rapidly idling. Previously I observed that rapidly idling loads can
allow the has_idle_cores test pass for short durations and the double
scanning means there is a greater chance of finding an idle CPU over the
two passes. I think overall it's better to avoid double scanning even if
there are counter examples as it's possible we'll get that back through
better depth selection in the future.
Thanks.
--
Mel Gorman
SUSE Labs
^ permalink raw reply [flat|nested] 10+ messages in thread