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Message-ID: <db28db41-41aa-4f3e-bb32-4bb58d746dbc@redhat.com>
Date: Fri, 30 Aug 2024 20:27:13 -0400
From: Waiman Long <longman@...hat.com>
To: Zefan Li <lizefan.x@...edance.com>, Tejun Heo <tj@...nel.org>,
Johannes Weiner <hannes@...xchg.org>, Michal Koutný
<mkoutny@...e.com>, Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>,
Frederic Weisbecker <frederic@...nel.org>
Cc: linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
Costa Shulyupin <cshulyup@...hat.com>
Subject: Re: [PATCH v2 1/2] sched/isolation: Exclude dynamically isolated CPUs
from housekeeping masks
On 8/21/24 10:23, Waiman Long wrote:
> The housekeeping CPU masks, set up by the "isolcpus" and "nohz_full"
> boot command line options, are used at boot time to exclude selected CPUs
> from running some kernel background processes to minimize disturbance
> to latency sensitive userspace applications. Some of housekeeping CPU
> masks are also checked at run time to avoid using those isolated CPUs.
>
> The cpuset subsystem is now able to dynamically create a set of isolated
> CPUs to be used in isolated cpuset partitions. The long term goal is
> to make the degree of isolation as close as possible to what can be
> done statically using those boot command line options.
>
> This patch is a step in that direction by making the housekeeping CPU
> mask APIs exclude the dynamically isolated CPUs when they are called
> at run time. The housekeeping CPU masks will fall back to the bootup
> default when all the dynamically isolated CPUs are released.
>
> A new housekeeping_exlude_isolcpus() function is added which is to be
> called by the cpuset subsystem to provide a list of isolated CPUs to
> be excluded.
>
> Signed-off-by: Waiman Long <longman@...hat.com>
> ---
> include/linux/sched/isolation.h | 8 +++
> kernel/sched/isolation.c | 112 +++++++++++++++++++++++++++++++-
> 2 files changed, 119 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h
> index 2b461129d1fa..d64fa4e60138 100644
> --- a/include/linux/sched/isolation.h
> +++ b/include/linux/sched/isolation.h
> @@ -27,6 +27,8 @@ extern bool housekeeping_enabled(enum hk_type type);
> extern void housekeeping_affine(struct task_struct *t, enum hk_type type);
> extern bool housekeeping_test_cpu(int cpu, enum hk_type type);
> extern void __init housekeeping_init(void);
> +extern int housekeeping_exlude_isolcpus(const struct cpumask *isolcpus,
> + unsigned long flags);
>
> #else
>
> @@ -54,6 +56,12 @@ static inline bool housekeeping_test_cpu(int cpu, enum hk_type type)
> }
>
> static inline void housekeeping_init(void) { }
> +
> +static inline int housekeeping_exlude_isolcpus(struct cpumask *isolcpus,
> + unsigned long flags)
> +{
> + return -EOPNOTSUPP;
> +}
> #endif /* CONFIG_CPU_ISOLATION */
>
> static inline bool housekeeping_cpu(int cpu, enum hk_type type)
> diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
> index 5891e715f00d..3018ba81eb65 100644
> --- a/kernel/sched/isolation.c
> +++ b/kernel/sched/isolation.c
> @@ -28,7 +28,16 @@ struct housekeeping {
> unsigned long flags;
> };
>
> -static struct housekeeping housekeeping;
> +static struct housekeeping housekeeping __read_mostly;
> +
> +/*
> + * Boot time housekeeping cpumask and flags
> + *
> + * If more than one of nohz_full or isolcpus are specified, the cpumask must
> + * be the same or the setup will fail.
> + */
> +static cpumask_var_t boot_hk_cpumask;
> +static unsigned long boot_hk_flags;
>
> bool housekeeping_enabled(enum hk_type type)
> {
> @@ -253,3 +262,104 @@ static int __init housekeeping_isolcpus_setup(char *str)
> return housekeeping_setup(str, flags);
> }
> __setup("isolcpus=", housekeeping_isolcpus_setup);
> +
> +/*
> + * Save bootup housekeeping cpumask and flags
> + */
> +static int housekeeping_save(void)
> +{
> + enum hk_type type;
> +
> + boot_hk_flags = housekeeping.flags;
> + for_each_set_bit(type, &housekeeping.flags, HK_TYPE_MAX) {
> + if (!alloc_cpumask_var(&boot_hk_cpumask, GFP_KERNEL))
> + return -ENOMEM;
> + cpumask_copy(boot_hk_cpumask, housekeeping.cpumasks[type]);
> + break;
> + }
> + return 0;
> +}
> +
> +/*
> + * Exclude the given dynamically isolated CPUs from the housekeeping CPUs
> + * External synchronization is required to make sure that concurrent call to
> + * this function will not happen.
> + *
> + * [TODO] The housekeeping cpumasks and flags at bootup time are currently
> + * preserved as cpuset dynamic CPU isolation isn't as good as boot time CPU
> + * isolation yet. Once dynamic CPU isolation is close to boot time isolation,
> + * we will not need to save the bootup values and will allow them to be
> + * overridden.
> + *
> + * Return: 0 if successful, an error code if not
> + */
> +int housekeeping_exlude_isolcpus(const struct cpumask *isolcpus, unsigned long flags)
> +{
> + static unsigned long alloc_flags;
> + static cpumask_var_t tmp_mask;
> + static bool excluded; /* @true if some CPUs have been excluded */
> + static bool inited; /* @true if called before */
> +
> + bool isolate_none = !isolcpus || cpumask_empty(isolcpus);
> + enum hk_type type;
> +
> + lockdep_assert_cpus_held();
> +
> + if (isolate_none && (!inited || !excluded))
> + return 0;
> +
> + if (unlikely(!inited)) {
> + if (!alloc_cpumask_var(&tmp_mask, GFP_KERNEL))
> + return -ENOMEM;
> + if (housekeeping.flags) {
> + int err = housekeeping_save();
> +
> + if (err)
> + return err;
> + }
> + alloc_flags = housekeeping.flags;
> + inited = true;
> + }
> +
> + if (isolate_none) {
> + excluded = false;
> +
> + /*
> + * Reset housekeeping to bootup default
> + */
> + for_each_set_bit(type, &boot_hk_flags, HK_TYPE_MAX)
> + cpumask_copy(housekeeping.cpumasks[type], boot_hk_cpumask);
> +
> + WRITE_ONCE(housekeeping.flags, boot_hk_flags);
> + if (!boot_hk_flags && static_key_enabled(&housekeeping_overridden))
> + static_key_disable_cpuslocked(&housekeeping_overridden.key);
> + return 0;
> + }
> +
> + /*
> + * Setting up the new housekeeping cpumasks
> + */
> + for_each_set_bit(type, &flags, HK_TYPE_MAX) {
> + const struct cpumask *src_mask;
> +
> + if (!(BIT(type) & alloc_flags)) {
> + if (!alloc_cpumask_var(&housekeeping.cpumasks[type], GFP_KERNEL))
> + return -ENOMEM;
> + alloc_flags |= BIT(type);
> + }
> + src_mask = (BIT(type) & boot_hk_flags)
> + ? boot_hk_cpumask : cpu_possible_mask;
> + /*
> + * Make sure there is at least one online housekeeping CPU
> + */
> + cpumask_andnot(tmp_mask, src_mask, isolcpus);
> + if (!cpumask_intersects(tmp_mask, cpu_online_mask))
> + return -EINVAL; /* Invalid isolated CPUs */
> + cpumask_copy(housekeeping.cpumasks[type], tmp_mask);
> + }
> + WRITE_ONCE(housekeeping.flags, boot_hk_flags | flags);
> + excluded = true;
> + if (!static_key_enabled(&housekeeping_overridden))
> + static_key_enable_cpuslocked(&housekeeping_overridden.key);
> + return 0;
> +}
Any comment or suggestion about this patch?
Thanks,
Longman
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