* [PATCH v2 0/2] sched/topology: Optimize topology_span_sane()
@ 2024-04-10 21:33 Kyle Meyer
2024-04-10 21:33 ` [PATCH v2 1/2] cpumask: Add for_each_cpu_from() Kyle Meyer
2024-04-10 21:33 ` [PATCH v2 2/2] sched/topology: Optimize topology_span_sane() Kyle Meyer
0 siblings, 2 replies; 9+ messages in thread
From: Kyle Meyer @ 2024-04-10 21:33 UTC (permalink / raw)
To: linux-kernel, yury.norov, andriy.shevchenko, linux, mingo,
peterz, juri.lelli, vincent.guittot, dietmar.eggemann, rostedt,
bsegall, mgorman, bristot, vschneid
Cc: russ.anderson, dimitri.sivanich, steve.wahl, Kyle Meyer
A soft lockup is being detected in build_sched_domains() on 32 socket
Sapphire Rapids systems with 3840 processors.
topology_span_sane(), called by build_sched_domains(), checks that each
processor's non-NUMA scheduling domains are completely equal or
completely disjoint. If a non-NUMA scheduling domain partially overlaps
another, scheduling groups can break.
This series adds for_each_cpu_from() as a generic cpumask macro to
optimize topology_span_sane() by removing duplicate comparisons. The
total number of comparisons is reduced from N * (N - 1) to
N * (N - 1) / 2 on each non-NUMA scheduling domain level, decreasing
the boot time by approximately 20 seconds and preventing the soft lockup
on the mentioned systems.
Changes in v2:
* 1/2: Change for_each_cpu()'s description.
* 2/2: Add more information to the commit message.
* https://lore.kernel.org/linux-kernel/20240409155250.3660517-1-kyle.meyer@hpe.com/T/
Kyle Meyer (2):
cpumask: Add for_each_cpu_from()
sched/topology: Optimize topology_span_sane()
include/linux/cpumask.h | 10 ++++++++++
kernel/sched/topology.c | 6 ++----
2 files changed, 12 insertions(+), 4 deletions(-)
--
2.44.0
^ permalink raw reply [flat|nested] 9+ messages in thread
* [PATCH v2 1/2] cpumask: Add for_each_cpu_from()
2024-04-10 21:33 [PATCH v2 0/2] sched/topology: Optimize topology_span_sane() Kyle Meyer
@ 2024-04-10 21:33 ` Kyle Meyer
2024-04-15 11:50 ` Valentin Schneider
2024-04-10 21:33 ` [PATCH v2 2/2] sched/topology: Optimize topology_span_sane() Kyle Meyer
1 sibling, 1 reply; 9+ messages in thread
From: Kyle Meyer @ 2024-04-10 21:33 UTC (permalink / raw)
To: linux-kernel, yury.norov, andriy.shevchenko, linux, mingo,
peterz, juri.lelli, vincent.guittot, dietmar.eggemann, rostedt,
bsegall, mgorman, bristot, vschneid
Cc: russ.anderson, dimitri.sivanich, steve.wahl, Kyle Meyer
Add for_each_cpu_from() as a generic cpumask macro.
for_each_cpu_from() is the same as for_each_cpu(), except it starts at
@cpu instead of zero.
Signed-off-by: Kyle Meyer <kyle.meyer@hpe.com>
Acked-by: Yury Norov <yury.norov@gmail.com>
---
include/linux/cpumask.h | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 1c29947db848..d75060fbd058 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -368,6 +368,16 @@ unsigned int __pure cpumask_next_wrap(int n, const struct cpumask *mask, int sta
#define for_each_cpu_or(cpu, mask1, mask2) \
for_each_or_bit(cpu, cpumask_bits(mask1), cpumask_bits(mask2), small_cpumask_bits)
+/**
+ * for_each_cpu_from - iterate over CPUs present in @mask, from @cpu to the end of @mask.
+ * @cpu: the (optionally unsigned) integer iterator
+ * @mask: the cpumask pointer
+ *
+ * After the loop, cpu is >= nr_cpu_ids.
+ */
+#define for_each_cpu_from(cpu, mask) \
+ for_each_set_bit_from(cpu, cpumask_bits(mask), small_cpumask_bits)
+
/**
* cpumask_any_but - return a "random" in a cpumask, but not this one.
* @mask: the cpumask to search
--
2.44.0
^ permalink raw reply related [flat|nested] 9+ messages in thread
* [PATCH v2 2/2] sched/topology: Optimize topology_span_sane()
2024-04-10 21:33 [PATCH v2 0/2] sched/topology: Optimize topology_span_sane() Kyle Meyer
2024-04-10 21:33 ` [PATCH v2 1/2] cpumask: Add for_each_cpu_from() Kyle Meyer
@ 2024-04-10 21:33 ` Kyle Meyer
2024-04-11 10:38 ` Andy Shevchenko
2024-04-15 11:50 ` Valentin Schneider
1 sibling, 2 replies; 9+ messages in thread
From: Kyle Meyer @ 2024-04-10 21:33 UTC (permalink / raw)
To: linux-kernel, yury.norov, andriy.shevchenko, linux, mingo,
peterz, juri.lelli, vincent.guittot, dietmar.eggemann, rostedt,
bsegall, mgorman, bristot, vschneid
Cc: russ.anderson, dimitri.sivanich, steve.wahl, Kyle Meyer
Optimize topology_span_sane() by removing duplicate comparisons.
Since topology_span_sane() is called inside of for_each_cpu(), each
pervious CPU has already been compared against every other CPU. The
current CPU only needs to be compared against higher-numbered CPUs.
The total number of comparisons is reduced from N * (N - 1) to
N * (N - 1) / 2 on each non-NUMA scheduling domain level.
Signed-off-by: Kyle Meyer <kyle.meyer@hpe.com>
Reviewed-by: Yury Norov <yury.norov@gmail.com>
Acked-by: Vincent Guittot <vincent.guittot@linaro.org>
---
kernel/sched/topology.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 99ea5986038c..b6bcafc09969 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -2347,7 +2347,7 @@ static struct sched_domain *build_sched_domain(struct sched_domain_topology_leve
static bool topology_span_sane(struct sched_domain_topology_level *tl,
const struct cpumask *cpu_map, int cpu)
{
- int i;
+ int i = cpu + 1;
/* NUMA levels are allowed to overlap */
if (tl->flags & SDTL_OVERLAP)
@@ -2359,9 +2359,7 @@ static bool topology_span_sane(struct sched_domain_topology_level *tl,
* breaking the sched_group lists - i.e. a later get_group() pass
* breaks the linking done for an earlier span.
*/
- for_each_cpu(i, cpu_map) {
- if (i == cpu)
- continue;
+ for_each_cpu_from(i, cpu_map) {
/*
* We should 'and' all those masks with 'cpu_map' to exactly
* match the topology we're about to build, but that can only
--
2.44.0
^ permalink raw reply related [flat|nested] 9+ messages in thread
* Re: [PATCH v2 2/2] sched/topology: Optimize topology_span_sane()
2024-04-10 21:33 ` [PATCH v2 2/2] sched/topology: Optimize topology_span_sane() Kyle Meyer
@ 2024-04-11 10:38 ` Andy Shevchenko
2024-04-11 21:55 ` Kyle Meyer
2024-04-15 11:50 ` Valentin Schneider
1 sibling, 1 reply; 9+ messages in thread
From: Andy Shevchenko @ 2024-04-11 10:38 UTC (permalink / raw)
To: Kyle Meyer
Cc: linux-kernel, yury.norov, linux, mingo, peterz, juri.lelli,
vincent.guittot, dietmar.eggemann, rostedt, bsegall, mgorman,
bristot, vschneid, russ.anderson, dimitri.sivanich, steve.wahl
On Wed, Apr 10, 2024 at 04:33:11PM -0500, Kyle Meyer wrote:
> Optimize topology_span_sane() by removing duplicate comparisons.
>
> Since topology_span_sane() is called inside of for_each_cpu(), each
> pervious CPU has already been compared against every other CPU. The
previous
> current CPU only needs to be compared against higher-numbered CPUs.
>
> The total number of comparisons is reduced from N * (N - 1) to
> N * (N - 1) / 2 on each non-NUMA scheduling domain level.
Thank you, now it makes sense.
--
With Best Regards,
Andy Shevchenko
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH v2 2/2] sched/topology: Optimize topology_span_sane()
2024-04-11 10:38 ` Andy Shevchenko
@ 2024-04-11 21:55 ` Kyle Meyer
2024-04-12 14:25 ` Andy Shevchenko
0 siblings, 1 reply; 9+ messages in thread
From: Kyle Meyer @ 2024-04-11 21:55 UTC (permalink / raw)
To: Andy Shevchenko
Cc: linux-kernel, yury.norov, linux, mingo, peterz, juri.lelli,
vincent.guittot, dietmar.eggemann, rostedt, bsegall, mgorman,
bristot, vschneid, russ.anderson, dimitri.sivanich, steve.wahl
On Thu, Apr 11, 2024 at 01:38:46PM +0300, Andy Shevchenko wrote:
> On Wed, Apr 10, 2024 at 04:33:11PM -0500, Kyle Meyer wrote:
> > Optimize topology_span_sane() by removing duplicate comparisons.
> >
> > Since topology_span_sane() is called inside of for_each_cpu(), each
> > pervious CPU has already been compared against every other CPU. The
>
> previous
Thank you for pointing that out. Should I send an updated version or can
a maintainer correct my mistake?
> > current CPU only needs to be compared against higher-numbered CPUs.
> >
> > The total number of comparisons is reduced from N * (N - 1) to
> > N * (N - 1) / 2 on each non-NUMA scheduling domain level.
>
> Thank you, now it makes sense.
Thanks,
Kyle Meyer
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH v2 2/2] sched/topology: Optimize topology_span_sane()
2024-04-11 21:55 ` Kyle Meyer
@ 2024-04-12 14:25 ` Andy Shevchenko
2024-04-13 17:42 ` Yury Norov
0 siblings, 1 reply; 9+ messages in thread
From: Andy Shevchenko @ 2024-04-12 14:25 UTC (permalink / raw)
To: Kyle Meyer
Cc: linux-kernel, yury.norov, linux, mingo, peterz, juri.lelli,
vincent.guittot, dietmar.eggemann, rostedt, bsegall, mgorman,
bristot, vschneid, russ.anderson, dimitri.sivanich, steve.wahl
On Thu, Apr 11, 2024 at 04:55:11PM -0500, Kyle Meyer wrote:
> On Thu, Apr 11, 2024 at 01:38:46PM +0300, Andy Shevchenko wrote:
> > On Wed, Apr 10, 2024 at 04:33:11PM -0500, Kyle Meyer wrote:
...
> > > Since topology_span_sane() is called inside of for_each_cpu(), each
> > > pervious CPU has already been compared against every other CPU. The
> >
> > previous
>
> Thank you for pointing that out. Should I send an updated version or can
> a maintainer correct my mistake?
Depends on the maintainer. I'm not the one here, don't expect answer from me.
> > > current CPU only needs to be compared against higher-numbered CPUs.
--
With Best Regards,
Andy Shevchenko
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH v2 2/2] sched/topology: Optimize topology_span_sane()
2024-04-12 14:25 ` Andy Shevchenko
@ 2024-04-13 17:42 ` Yury Norov
0 siblings, 0 replies; 9+ messages in thread
From: Yury Norov @ 2024-04-13 17:42 UTC (permalink / raw)
To: Andy Shevchenko
Cc: Kyle Meyer, linux-kernel, linux, mingo, peterz, juri.lelli,
vincent.guittot, dietmar.eggemann, rostedt, bsegall, mgorman,
bristot, vschneid, russ.anderson, dimitri.sivanich, steve.wahl
On Fri, Apr 12, 2024 at 05:25:26PM +0300, Andy Shevchenko wrote:
> On Thu, Apr 11, 2024 at 04:55:11PM -0500, Kyle Meyer wrote:
> > On Thu, Apr 11, 2024 at 01:38:46PM +0300, Andy Shevchenko wrote:
> > > On Wed, Apr 10, 2024 at 04:33:11PM -0500, Kyle Meyer wrote:
>
> ...
>
> > > > Since topology_span_sane() is called inside of for_each_cpu(), each
> > > > pervious CPU has already been compared against every other CPU. The
> > >
> > > previous
> >
> > Thank you for pointing that out. Should I send an updated version or can
> > a maintainer correct my mistake?
>
> Depends on the maintainer. I'm not the one here, don't expect answer from me.
I like this rework, and I'll take it in bitmap-for-next for testing.
I see Vincent already acked it, so I can also move it upstream, if no
objections from Peter, Juri and Ingo.
Thanks,
Yury
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH v2 1/2] cpumask: Add for_each_cpu_from()
2024-04-10 21:33 ` [PATCH v2 1/2] cpumask: Add for_each_cpu_from() Kyle Meyer
@ 2024-04-15 11:50 ` Valentin Schneider
0 siblings, 0 replies; 9+ messages in thread
From: Valentin Schneider @ 2024-04-15 11:50 UTC (permalink / raw)
To: Kyle Meyer, linux-kernel, yury.norov, andriy.shevchenko, linux,
mingo, peterz, juri.lelli, vincent.guittot, dietmar.eggemann,
rostedt, bsegall, mgorman, bristot
Cc: russ.anderson, dimitri.sivanich, steve.wahl, Kyle Meyer
On 10/04/24 16:33, Kyle Meyer wrote:
> Add for_each_cpu_from() as a generic cpumask macro.
>
> for_each_cpu_from() is the same as for_each_cpu(), except it starts at
> @cpu instead of zero.
>
> Signed-off-by: Kyle Meyer <kyle.meyer@hpe.com>
> Acked-by: Yury Norov <yury.norov@gmail.com>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH v2 2/2] sched/topology: Optimize topology_span_sane()
2024-04-10 21:33 ` [PATCH v2 2/2] sched/topology: Optimize topology_span_sane() Kyle Meyer
2024-04-11 10:38 ` Andy Shevchenko
@ 2024-04-15 11:50 ` Valentin Schneider
1 sibling, 0 replies; 9+ messages in thread
From: Valentin Schneider @ 2024-04-15 11:50 UTC (permalink / raw)
To: Kyle Meyer, linux-kernel, yury.norov, andriy.shevchenko, linux,
mingo, peterz, juri.lelli, vincent.guittot, dietmar.eggemann,
rostedt, bsegall, mgorman, bristot
Cc: russ.anderson, dimitri.sivanich, steve.wahl, Kyle Meyer
On 10/04/24 16:33, Kyle Meyer wrote:
> Optimize topology_span_sane() by removing duplicate comparisons.
>
> Since topology_span_sane() is called inside of for_each_cpu(), each
> pervious CPU has already been compared against every other CPU. The
> current CPU only needs to be compared against higher-numbered CPUs.
>
> The total number of comparisons is reduced from N * (N - 1) to
> N * (N - 1) / 2 on each non-NUMA scheduling domain level.
>
> Signed-off-by: Kyle Meyer <kyle.meyer@hpe.com>
> Reviewed-by: Yury Norov <yury.norov@gmail.com>
> Acked-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
^ permalink raw reply [flat|nested] 9+ messages in thread
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2024-04-10 21:33 [PATCH v2 0/2] sched/topology: Optimize topology_span_sane() Kyle Meyer
2024-04-10 21:33 ` [PATCH v2 1/2] cpumask: Add for_each_cpu_from() Kyle Meyer
2024-04-15 11:50 ` Valentin Schneider
2024-04-10 21:33 ` [PATCH v2 2/2] sched/topology: Optimize topology_span_sane() Kyle Meyer
2024-04-11 10:38 ` Andy Shevchenko
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