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Message-ID: <f9d9c6e959e441ec94264891ae90c11d@hisilicon.com>
Date: Wed, 2 Dec 2020 09:20:39 +0000
From: "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>
To: Vincent Guittot <vincent.guittot@...aro.org>
CC: Valentin Schneider <valentin.schneider@....com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
"Rafael J. Wysocki" <rjw@...ysocki.net>,
"Cc: Len Brown" <lenb@...nel.org>,
"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
Jonathan Cameron <jonathan.cameron@...wei.com>,
Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
Mark Rutland <mark.rutland@....com>,
LAK <linux-arm-kernel@...ts.infradead.org>,
linux-kernel <linux-kernel@...r.kernel.org>,
ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
Linuxarm <linuxarm@...wei.com>, "xuwei (O)" <xuwei5@...wei.com>,
"Zengtao (B)" <prime.zeng@...ilicon.com>
Subject: RE: [RFC PATCH v2 2/2] scheduler: add scheduler level for clusters
> -----Original Message-----
> From: Vincent Guittot [mailto:vincent.guittot@...aro.org]
> Sent: Wednesday, December 2, 2020 9:27 PM
> To: Song Bao Hua (Barry Song) <song.bao.hua@...ilicon.com>
> Cc: Valentin Schneider <valentin.schneider@....com>; Catalin Marinas
> <catalin.marinas@....com>; Will Deacon <will@...nel.org>; Rafael J. Wysocki
> <rjw@...ysocki.net>; Cc: Len Brown <lenb@...nel.org>;
> gregkh@...uxfoundation.org; Jonathan Cameron <jonathan.cameron@...wei.com>;
> Ingo Molnar <mingo@...hat.com>; Peter Zijlstra <peterz@...radead.org>; Juri
> Lelli <juri.lelli@...hat.com>; Dietmar Eggemann <dietmar.eggemann@....com>;
> Steven Rostedt <rostedt@...dmis.org>; Ben Segall <bsegall@...gle.com>; Mel
> Gorman <mgorman@...e.de>; Mark Rutland <mark.rutland@....com>; LAK
> <linux-arm-kernel@...ts.infradead.org>; linux-kernel
> <linux-kernel@...r.kernel.org>; ACPI Devel Maling List
> <linux-acpi@...r.kernel.org>; Linuxarm <linuxarm@...wei.com>; xuwei (O)
> <xuwei5@...wei.com>; Zengtao (B) <prime.zeng@...ilicon.com>
> Subject: Re: [RFC PATCH v2 2/2] scheduler: add scheduler level for clusters
>
> On Tue, 1 Dec 2020 at 04:04, Barry Song <song.bao.hua@...ilicon.com> wrote:
> >
> > ARM64 server chip Kunpeng 920 has 6 clusters in each NUMA node, and each
> > cluster has 4 cpus. All clusters share L3 cache data, but each cluster
> > has local L3 tag. On the other hand, each clusters will share some
> > internal system bus. This means cache coherence overhead inside one cluster
> > is much less than the overhead across clusters.
> >
> > +-----------------------------------+ +---------+
> > | +------+ +------+ +---------------------------+ |
> > | | CPU0 | | cpu1 | | +-----------+ | |
> > | +------+ +------+ | | | | |
> > | +----+ L3 | | |
> > | +------+ +------+ cluster | | tag | | |
> > | | CPU2 | | CPU3 | | | | | |
> > | +------+ +------+ | +-----------+ | |
> > | | | |
> > +-----------------------------------+ | |
> > +-----------------------------------+ | |
> > | +------+ +------+ +--------------------------+ |
> > | | | | | | +-----------+ | |
> > | +------+ +------+ | | | | |
> > | | | L3 | | |
> > | +------+ +------+ +----+ tag | | |
> > | | | | | | | | | |
> > | +------+ +------+ | +-----------+ | |
> > | | | |
> > +-----------------------------------+ | L3 |
> > | data |
> > +-----------------------------------+ | |
> > | +------+ +------+ | +-----------+ | |
> > | | | | | | | | | |
> > | +------+ +------+ +----+ L3 | | |
> > | | | tag | | |
> > | +------+ +------+ | | | | |
> > | | | | | ++ +-----------+ | |
> > | +------+ +------+ |---------------------------+ |
> > +-----------------------------------| | |
> > +-----------------------------------| | |
> > | +------+ +------+ +---------------------------+ |
> > | | | | | | +-----------+ | |
> > | +------+ +------+ | | | | |
> > | +----+ L3 | | |
> > | +------+ +------+ | | tag | | |
> > | | | | | | | | | |
> > | +------+ +------+ | +-----------+ | |
> > | | | |
> > +-----------------------------------+ | |
> > +-----------------------------------+ | |
> > | +------+ +------+ +--------------------------+ |
> > | | | | | | +-----------+ | |
> > | +------+ +------+ | | | | |
> > | | | L3 | | |
> > | +------+ +------+ +---+ tag | | |
> > | | | | | | | | | |
> > | +------+ +------+ | +-----------+ | |
> > | | | |
> > +-----------------------------------+ | |
> > +-----------------------------------+ ++ |
> > | +------+ +------+ +--------------------------+ |
> > | | | | | | +-----------+ | |
> > | +------+ +------+ | | | | |
> > | | | L3 | | |
> > | +------+ +------+ +--+ tag | | |
> > | | | | | | | | | |
> > | +------+ +------+ | +-----------+ | |
> > | | +---------+
> > +-----------------------------------+
> >
> > This patch adds the sched_domain for clusters. On kunpeng 920, without
> > this patch, domain0 of cpu0 would be MC for cpu0-cpu23 with
> > min_interval=24, max_interval=48; with this patch, MC becomes domain1,
> > a new domain0 "CL" including cpu0-cpu3 is added with min_interval=4 and
> > max_interval=8.
> > This will affect load balance. For example, without this patch, while cpu0
> > becomes idle, it will pull a task from cpu1-cpu15. With this patch, cpu0
> > will try to pull a task from cpu1-cpu3 first. This will have much less
> > overhead of task migration.
> >
> > On the other hand, while doing WAKE_AFFINE, this patch will try to find
> > a core in the target cluster before scanning the llc domain.
> > This means it will proactively use a core which has better affinity with
> > target core at first.
>
> Which is at the opposite of what we are usually trying to do in the
> fast wakeup path: trying to minimize resource sharing by finding an
> idle core with all smt idle as an example
In wake_affine case, I guess we are actually want some kind of
resource sharing such as LLC to get waker and wakee get closer
to each other. find_idlest_cpu() is really opposite.
So the real question is that LLC is always the right choice of
idle sibling?
In this case, 6 clusters are in same LLC, but hardware has different
behavior for inside single cluster and across multiple clusters.
>
> >
> > Not much benchmark has been done yet. but here is a rough hackbench
> > result.
> > we run the below command with different -g parameter to increase system load
> > by changing g from 1 to 4, for each one of 1-4, we run the benchmark ten times
> > and record the data to get the average time:
> >
> > First, we run hackbench in only one NUMA node(cpu0-cpu23):
> > $ numactl -N 0 hackbench -p -T -l 100000 -g $1
>
> What is your ref tree ? v5.10-rcX or tip/sched/core ?
Actually I was using 5.9 release. That must be weird.
But the reason is that disk driver is getting hang
in my hardware in 5.10-rcx.
>
> >
> > g=1 (seen cpu utilization around 50% for each core)
> > Running in threaded mode with 1 groups using 40 file descriptors
> > Each sender will pass 100000 messages of 100 bytes
> > w/o: 7.689 7.485 7.485 7.458 7.524 7.539 7.738 7.693 7.568 7.674=7.5853
> > w/ : 7.516 7.941 7.374 7.963 7.881 7.910 7.420 7.556 7.695 7.441=7.6697
> > performance improvement w/ patch: -1.01%
> >
> > g=2 (seen cpu utilization around 70% for each core)
> > Running in threaded mode with 2 groups using 40 file descriptors
> > Each sender will pass 100000 messages of 100 bytes
> > w/o: 10.127 10.119 10.070 10.196 10.057 10.111 10.045 10.164 10.162
> 9.955=10.1006
> > w/ : 9.694 9.654 9.612 9.649 9.686 9.734 9.607 9.842 9.690 9.710=9.6878
> > performance improvement w/ patch: 4.08%
> >
> > g=3 (seen cpu utilization around 90% for each core)
> > Running in threaded mode with 3 groups using 40 file descriptors
> > Each sender will pass 100000 messages of 100 bytes
> > w/o: 15.885 15.254 15.932 15.647 16.120 15.878 15.857 15.759 15.674
> 15.721=15.7727
> > w/ : 14.974 14.657 13.969 14.985 14.728 15.665 15.191 14.995 14.946
> 14.895=14.9005
> > performance improvement w/ patch: 5.53%
> >
> > g=4
> > Running in threaded mode with 4 groups using 40 file descriptors
> > Each sender will pass 100000 messages of 100 bytes
> > w/o: 20.014 21.025 21.119 21.235 19.767 20.971 20.962 20.914 21.090
> 21.090=20.8187
> > w/ : 20.331 20.608 20.338 20.445 20.456 20.146 20.693 20.797 21.381
> 20.452=20.5647
> > performance improvement w/ patch: 1.22%
> >
> > After that, we run the same hackbench in both NUMA nodes(cpu0-cpu47):
> > g=1
> > w/o: 7.351 7.416 7.486 7.358 7.516 7.403 7.413 7.411 7.421 7.454=7.4229
> > w/ : 7.609 7.596 7.647 7.571 7.687 7.571 7.520 7.513 7.530 7.681=7.5925
> > performance improvement by patch: -2.2%
> >
> > g=2
> > w/o: 9.046 9.190 9.053 8.950 9.101 8.930 9.143 8.928 8.905 9.034=9.028
> > w/ : 8.247 8.057 8.258 8.310 8.083 8.201 8.044 8.158 8.382 8.173=8.1913
> > performance improvement by patch: 9.3%
> >
> > g=3
> > w/o: 11.664 11.767 11.277 11.619 12.557 12.760 11.664 12.165 12.235
> 11.849=11.9557
> > w/ : 9.387 9.461 9.650 9.613 9.591 9.454 9.496 9.716 9.327 9.722=9.5417
> > performance improvement by patch: 20.2%
> >
> > g=4
> > w/o: 17.347 17.299 17.655 18.775 16.707 18.879 17.255 18.356 16.859
> 18.515=17.7647
> > w/ : 10.416 10.496 10.601 10.318 10.459 10.617 10.510 10.642 10.467
> 10.401=10.4927
> > performance improvement by patch: 40.9%
> >
> > g=5
> > w/o: 27.805 26.633 24.138 28.086 24.405 27.922 30.043 28.458 31.073
> 25.819=27.4382
> > w/ : 13.817 13.976 14.166 13.688 14.132 14.095 14.003 13.997 13.954
> 13.907=13.9735
> > performance improvement by patch: 49.1%
> >
> > It seems the patch can bring a huge increase on hackbench especially when
> > we bind hackbench to all of cpu0-cpu47, comparing to 5.53% while running
> > on single NUMA node(cpu0-cpu23)
>
> Interesting that this patch mainly impacts the numa case
>
> >
> > Signed-off-by: Barry Song <song.bao.hua@...ilicon.com>
> > ---
> > arch/arm64/Kconfig | 7 +++++++
> > arch/arm64/kernel/smp.c | 17 +++++++++++++++++
> > include/linux/topology.h | 7 +++++++
> > kernel/sched/fair.c | 35 +++++++++++++++++++++++++++++++++++
> > 4 files changed, 66 insertions(+)
> >
> > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> > index 6d23283..3583c26 100644
> > --- a/arch/arm64/Kconfig
> > +++ b/arch/arm64/Kconfig
> > @@ -938,6 +938,13 @@ config SCHED_MC
> > making when dealing with multi-core CPU chips at a cost of slightly
> > increased overhead in some places. If unsure say N here.
> >
> > +config SCHED_CLUSTER
> > + bool "Cluster scheduler support"
> > + help
> > + Cluster scheduler support improves the CPU scheduler's decision
> > + making when dealing with machines that have clusters(sharing internal
> > + bus or sharing LLC cache tag). If unsure say N here.
> > +
> > config SCHED_SMT
> > bool "SMT scheduler support"
> > help
> > diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> > index 355ee9e..5c8f026 100644
> > --- a/arch/arm64/kernel/smp.c
> > +++ b/arch/arm64/kernel/smp.c
> > @@ -32,6 +32,7 @@
> > #include <linux/irq_work.h>
> > #include <linux/kexec.h>
> > #include <linux/kvm_host.h>
> > +#include <linux/sched/topology.h>
> >
> > #include <asm/alternative.h>
> > #include <asm/atomic.h>
> > @@ -726,6 +727,20 @@ void __init smp_init_cpus(void)
> > }
> > }
> >
> > +static struct sched_domain_topology_level arm64_topology[] = {
> > +#ifdef CONFIG_SCHED_SMT
> > + { cpu_smt_mask, cpu_smt_flags, SD_INIT_NAME(SMT) },
> > +#endif
> > +#ifdef CONFIG_SCHED_CLUSTER
> > + { cpu_clustergroup_mask, cpu_core_flags, SD_INIT_NAME(CL) },
> > +#endif
> > +#ifdef CONFIG_SCHED_MC
> > + { cpu_coregroup_mask, cpu_core_flags, SD_INIT_NAME(MC) },
> > +#endif
> > + { cpu_cpu_mask, SD_INIT_NAME(DIE) },
> > + { NULL, },
> > +};
> > +
> > void __init smp_prepare_cpus(unsigned int max_cpus)
> > {
> > const struct cpu_operations *ops;
> > @@ -735,6 +750,8 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
> >
> > init_cpu_topology();
> >
> > + set_sched_topology(arm64_topology);
> > +
> > this_cpu = smp_processor_id();
> > store_cpu_topology(this_cpu);
> > numa_store_cpu_info(this_cpu);
> > diff --git a/include/linux/topology.h b/include/linux/topology.h
> > index 5f66648..2c823c0 100644
> > --- a/include/linux/topology.h
> > +++ b/include/linux/topology.h
> > @@ -211,6 +211,13 @@ static inline const struct cpumask *cpu_smt_mask(int
> cpu)
> > }
> > #endif
> >
> > +#ifdef CONFIG_SCHED_CLUSTER
> > +static inline const struct cpumask *cpu_cluster_mask(int cpu)
> > +{
> > + return topology_cluster_cpumask(cpu);
> > +}
> > +#endif
> > +
> > static inline const struct cpumask *cpu_cpu_mask(int cpu)
> > {
> > return cpumask_of_node(cpu_to_node(cpu));
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 1a68a05..ae8ec910 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -6106,6 +6106,37 @@ static inline int select_idle_smt(struct task_struct
> *p, int target)
> >
> > #endif /* CONFIG_SCHED_SMT */
> >
> > +#ifdef CONFIG_SCHED_CLUSTER
> > +/*
> > + * Scan the local CLUSTER mask for idle CPUs.
> > + */
> > +static int select_idle_cluster(struct task_struct *p, int target)
> > +{
> > + int cpu;
> > +
> > + /* right now, no hardware with both cluster and smt to run */
> > + if (sched_smt_active())
>
> don't use smt static key but a dedicated one if needed
Sure.
>
> > + return -1;
> > +
> > + for_each_cpu_wrap(cpu, cpu_cluster_mask(target), target) {
> > + if (!cpumask_test_cpu(cpu, p->cpus_ptr))
> > + continue;
> > + if (available_idle_cpu(cpu))
> > + return cpu;
> > + }
> > +
> > + return -1;
> > +}
> > +
> > +#else /* CONFIG_SCHED_CLUSTER */
> > +
> > +static inline int select_idle_cluster(struct task_struct *p, int target)
> > +{
> > + return -1;
> > +}
> > +
> > +#endif /* CONFIG_SCHED_CLUSTER */
> > +
> > /*
> > * Scan the LLC domain for idle CPUs; this is dynamically regulated by
> > * comparing the average scan cost (tracked in sd->avg_scan_cost) against
> the
> > @@ -6270,6 +6301,10 @@ static int select_idle_sibling(struct task_struct *p,
> int prev, int target)
> > if ((unsigned)i < nr_cpumask_bits)
> > return i;
> >
> > + i = select_idle_cluster(p, target);
> > + if ((unsigned)i < nr_cpumask_bits)
> > + return i;
>
> This is yet another loop in the fast wake up path.
>
> I'm curious to know which part of this patch really gives the perf improvement ?
> -Is it the new sched domain level with a shorter interval that is then
> used by Load balance to better spread task in the cluster and between
> clusters ?
> -Or this new loop in the wake up path which tries to keep threads in
> the same cluster ? which is at the opposite of the rest of the
> scheduler which tries to spread
If I don't scan cluster first for wake_affine, I almost don't see large
hackbench change by the new sche_domain.
For example:
g=4 in hackbench on cpu0-cpu47(two numa)
w/o patch: 17.7647 (average time in 10 times of hackbench)
w/ the full patch: 10.4927
w/ patch but drop select_idle_cluster(): 15.0931
So I don't think the hackbench increase mainly comes from the shorter
interval of load balance of the new cluster domain.
What does really matter is select_idle_cluster() according to my tests.
>
> Also could the sched_feat(SIS_PROP) impacts significantly your
> topology because it breaks before looking for all cores in the LLC ?
> And this new loop extends the number of tested core ?
In this case, cluster must belong to LLC. Cluster is the child of LLC.
Maybe the code Valentin suggested in his reply is a good way to
keep the code align with the existing select_idle_cpu():
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);
- struct sched_domain *this_sd;
+ struct sched_domain *this_sd, *child = NULL;
u64 avg_cost, avg_idle;
u64 time;
int this = smp_processor_id();
@@ -6150,14 +6150,22 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
time = cpu_clock(this);
- cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
+ do {
+ /* XXX: sd should start as SMT's parent */
+ cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
+ if (child)
+ cpumask_andnot(cpus, cpus, sched_domain_span(child));
+
+ for_each_cpu_wrap(cpu, cpus, target) {
+ if (!--nr)
+ return -1;
+ if (available_idle_cpu(cpu) || sched_idle_cpu(cpu))
+ break;
+ }
- for_each_cpu_wrap(cpu, cpus, target) {
- if (!--nr)
- return -1;
- if (available_idle_cpu(cpu) || sched_idle_cpu(cpu))
- break;
- }
+ child = sd;
+ sd = sd->parent;
+ } while (sd && sd->flags & SD_SHARE_PKG_RESOURCES);
>
> > +
> > i = select_idle_cpu(p, sd, target);
> > if ((unsigned)i < nr_cpumask_bits)
> > return i;
> > --
> > 2.7.4
> >
Thanks
Barry
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