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Message-ID: <20250728132129.GC11434@pauld.westford.csb>
Date: Mon, 28 Jul 2025 09:21:29 -0400
From: Phil Auld <pauld@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: John Stultz <jstultz@...gle.com>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
K Prateek Nayak <kprateek.nayak@....com>
Subject: Re: [tip: sched/core] sched: Add CONFIG_SCHED_PROXY_EXEC & boot
argument to enable/disable
On Wed, Jul 16, 2025 at 10:19:14AM -0000 tip-bot2 for John Stultz wrote:
> The following commit has been merged into the sched/core branch of tip:
>
Cool! Good work John. "That was easy" ;)
Cheers,
Phil
> Commit-ID: 25c411fce735dda29de26f58d3fce52d4824380c
> Gitweb: https://git.kernel.org/tip/25c411fce735dda29de26f58d3fce52d4824380c
> Author: John Stultz <jstultz@...gle.com>
> AuthorDate: Sat, 12 Jul 2025 03:33:42
> Committer: Peter Zijlstra <peterz@...radead.org>
> CommitterDate: Mon, 14 Jul 2025 17:16:31 +02:00
>
> sched: Add CONFIG_SCHED_PROXY_EXEC & boot argument to enable/disable
>
> Add a CONFIG_SCHED_PROXY_EXEC option, along with a boot argument
> sched_proxy_exec= that can be used to disable the feature at boot
> time if CONFIG_SCHED_PROXY_EXEC was enabled.
>
> Also uses this option to allow the rq->donor to be different from
> rq->curr.
>
> Signed-off-by: John Stultz <jstultz@...gle.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Tested-by: K Prateek Nayak <kprateek.nayak@....com>
> Link: https://lkml.kernel.org/r/20250712033407.2383110-2-jstultz@google.com
> ---
> Documentation/admin-guide/kernel-parameters.txt | 5 +++-
> include/linux/sched.h | 13 +++++++-
> init/Kconfig | 12 +++++++-
> kernel/sched/core.c | 29 ++++++++++++++++-
> kernel/sched/sched.h | 12 +++++++-
> 5 files changed, 71 insertions(+)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 07e22ba..00b8357 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -6387,6 +6387,11 @@
> sa1100ir [NET]
> See drivers/net/irda/sa1100_ir.c.
>
> + sched_proxy_exec= [KNL]
> + Enables or disables "proxy execution" style
> + solution to mutex-based priority inversion.
> + Format: <bool>
> +
> sched_verbose [KNL,EARLY] Enables verbose scheduler debug messages.
>
> schedstats= [KNL,X86] Enable or disable scheduled statistics.
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 54a9126..f225b6b 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1656,6 +1656,19 @@ struct task_struct {
> randomized_struct_fields_end
> } __attribute__ ((aligned (64)));
>
> +#ifdef CONFIG_SCHED_PROXY_EXEC
> +DECLARE_STATIC_KEY_TRUE(__sched_proxy_exec);
> +static inline bool sched_proxy_exec(void)
> +{
> + return static_branch_likely(&__sched_proxy_exec);
> +}
> +#else
> +static inline bool sched_proxy_exec(void)
> +{
> + return false;
> +}
> +#endif
> +
> #define TASK_REPORT_IDLE (TASK_REPORT + 1)
> #define TASK_REPORT_MAX (TASK_REPORT_IDLE << 1)
>
> diff --git a/init/Kconfig b/init/Kconfig
> index 965699c..24dd42d 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -878,6 +878,18 @@ config UCLAMP_BUCKETS_COUNT
>
> If in doubt, use the default value.
>
> +config SCHED_PROXY_EXEC
> + bool "Proxy Execution"
> + # Avoid some build failures w/ PREEMPT_RT until it can be fixed
> + depends on !PREEMPT_RT
> + # Need to investigate how to inform sched_ext of split contexts
> + depends on !SCHED_CLASS_EXT
> + # Not particularly useful until we get to multi-rq proxying
> + depends on EXPERT
> + help
> + This option enables proxy execution, a mechanism for mutex-owning
> + tasks to inherit the scheduling context of higher priority waiters.
> +
> endmenu
>
> #
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index e9c8bda..dd9f5c0 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -119,6 +119,35 @@ EXPORT_TRACEPOINT_SYMBOL_GPL(sched_compute_energy_tp);
>
> DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);
>
> +#ifdef CONFIG_SCHED_PROXY_EXEC
> +DEFINE_STATIC_KEY_TRUE(__sched_proxy_exec);
> +static int __init setup_proxy_exec(char *str)
> +{
> + bool proxy_enable = true;
> +
> + if (*str && kstrtobool(str + 1, &proxy_enable)) {
> + pr_warn("Unable to parse sched_proxy_exec=\n");
> + return 0;
> + }
> +
> + if (proxy_enable) {
> + pr_info("sched_proxy_exec enabled via boot arg\n");
> + static_branch_enable(&__sched_proxy_exec);
> + } else {
> + pr_info("sched_proxy_exec disabled via boot arg\n");
> + static_branch_disable(&__sched_proxy_exec);
> + }
> + return 1;
> +}
> +#else
> +static int __init setup_proxy_exec(char *str)
> +{
> + pr_warn("CONFIG_SCHED_PROXY_EXEC=n, so it cannot be enabled or disabled at boot time\n");
> + return 0;
> +}
> +#endif
> +__setup("sched_proxy_exec", setup_proxy_exec);
> +
> /*
> * Debugging: various feature bits
> *
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index ac953fa..e53d0b8 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1142,10 +1142,15 @@ struct rq {
> */
> unsigned long nr_uninterruptible;
>
> +#ifdef CONFIG_SCHED_PROXY_EXEC
> + struct task_struct __rcu *donor; /* Scheduling context */
> + struct task_struct __rcu *curr; /* Execution context */
> +#else
> union {
> struct task_struct __rcu *donor; /* Scheduler context */
> struct task_struct __rcu *curr; /* Execution context */
> };
> +#endif
> struct sched_dl_entity *dl_server;
> struct task_struct *idle;
> struct task_struct *stop;
> @@ -1326,10 +1331,17 @@ DECLARE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);
> #define cpu_curr(cpu) (cpu_rq(cpu)->curr)
> #define raw_rq() raw_cpu_ptr(&runqueues)
>
> +#ifdef CONFIG_SCHED_PROXY_EXEC
> +static inline void rq_set_donor(struct rq *rq, struct task_struct *t)
> +{
> + rcu_assign_pointer(rq->donor, t);
> +}
> +#else
> static inline void rq_set_donor(struct rq *rq, struct task_struct *t)
> {
> /* Do nothing */
> }
> +#endif
>
> #ifdef CONFIG_SCHED_CORE
> static inline struct cpumask *sched_group_span(struct sched_group *sg);
>
--
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