The include/generated/asm-offsets.h is generated in Kbuild during compiling from arch/SRCARCH/kernel/asm-offsets.c. When we want to generate another similar offset header file, circular dependency can happen. For example, we want to generate a offset file include/generated/test.h, which is included in include/sched/sched.h. If we generate asm-offsets.h first, it will fail, as include/sched/sched.h is included in asm-offsets.c and include/generated/test.h doesn't exist; If we generate test.h first, it can't success neither, as include/generated/asm-offsets.h is included by it. In x86_64, the macro COMPILE_OFFSETS is used to avoid such circular dependency. We can generate asm-offsets.h first, and if the COMPILE_OFFSETS is defined, we don't include the "generated/test.h". And we define the macro COMPILE_OFFSETS for all the asm-offsets.c for this purpose. Signed-off-by: Menglong Dong --- arch/alpha/kernel/asm-offsets.c | 1 + arch/arc/kernel/asm-offsets.c | 1 + arch/arm/kernel/asm-offsets.c | 2 ++ arch/arm64/kernel/asm-offsets.c | 1 + arch/csky/kernel/asm-offsets.c | 1 + arch/hexagon/kernel/asm-offsets.c | 1 + arch/loongarch/kernel/asm-offsets.c | 2 ++ arch/m68k/kernel/asm-offsets.c | 1 + arch/microblaze/kernel/asm-offsets.c | 1 + arch/mips/kernel/asm-offsets.c | 2 ++ arch/nios2/kernel/asm-offsets.c | 1 + arch/openrisc/kernel/asm-offsets.c | 1 + arch/parisc/kernel/asm-offsets.c | 1 + arch/powerpc/kernel/asm-offsets.c | 1 + arch/riscv/kernel/asm-offsets.c | 1 + arch/s390/kernel/asm-offsets.c | 1 + arch/sh/kernel/asm-offsets.c | 1 + arch/sparc/kernel/asm-offsets.c | 1 + arch/um/kernel/asm-offsets.c | 2 ++ arch/xtensa/kernel/asm-offsets.c | 1 + 20 files changed, 24 insertions(+) diff --git a/arch/alpha/kernel/asm-offsets.c b/arch/alpha/kernel/asm-offsets.c index e9dad60b147f..1ebb05890499 100644 --- a/arch/alpha/kernel/asm-offsets.c +++ b/arch/alpha/kernel/asm-offsets.c @@ -4,6 +4,7 @@ * This code generates raw asm output which is post-processed to extract * and format the required data. */ +#define COMPILE_OFFSETS #include #include diff --git a/arch/arc/kernel/asm-offsets.c b/arch/arc/kernel/asm-offsets.c index f77deb799175..2978da85fcb6 100644 --- a/arch/arc/kernel/asm-offsets.c +++ b/arch/arc/kernel/asm-offsets.c @@ -2,6 +2,7 @@ /* * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com) */ +#define COMPILE_OFFSETS #include #include diff --git a/arch/arm/kernel/asm-offsets.c b/arch/arm/kernel/asm-offsets.c index 123f4a8ef446..2101938d27fc 100644 --- a/arch/arm/kernel/asm-offsets.c +++ b/arch/arm/kernel/asm-offsets.c @@ -7,6 +7,8 @@ * This code generates raw asm output which is post-processed to extract * and format the required data. */ +#define COMPILE_OFFSETS + #include #include #include diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c index 30d4bbe68661..b6367ff3a49c 100644 --- a/arch/arm64/kernel/asm-offsets.c +++ b/arch/arm64/kernel/asm-offsets.c @@ -6,6 +6,7 @@ * 2001-2002 Keith Owens * Copyright (C) 2012 ARM Ltd. */ +#define COMPILE_OFFSETS #include #include diff --git a/arch/csky/kernel/asm-offsets.c b/arch/csky/kernel/asm-offsets.c index d1e903579473..5525c8e7e1d9 100644 --- a/arch/csky/kernel/asm-offsets.c +++ b/arch/csky/kernel/asm-offsets.c @@ -1,5 +1,6 @@ // SPDX-License-Identifier: GPL-2.0 // Copyright (C) 2018 Hangzhou C-SKY Microsystems co.,ltd. +#define COMPILE_OFFSETS #include #include diff --git a/arch/hexagon/kernel/asm-offsets.c b/arch/hexagon/kernel/asm-offsets.c index 03a7063f9456..50eea9fa6f13 100644 --- a/arch/hexagon/kernel/asm-offsets.c +++ b/arch/hexagon/kernel/asm-offsets.c @@ -8,6 +8,7 @@ * * Copyright (c) 2010-2012, The Linux Foundation. All rights reserved. */ +#define COMPILE_OFFSETS #include #include diff --git a/arch/loongarch/kernel/asm-offsets.c b/arch/loongarch/kernel/asm-offsets.c index db1e4bb26b6a..3017c7157600 100644 --- a/arch/loongarch/kernel/asm-offsets.c +++ b/arch/loongarch/kernel/asm-offsets.c @@ -4,6 +4,8 @@ * * Copyright (C) 2020-2022 Loongson Technology Corporation Limited */ +#define COMPILE_OFFSETS + #include #include #include diff --git a/arch/m68k/kernel/asm-offsets.c b/arch/m68k/kernel/asm-offsets.c index 906d73230537..67a1990f9d74 100644 --- a/arch/m68k/kernel/asm-offsets.c +++ b/arch/m68k/kernel/asm-offsets.c @@ -9,6 +9,7 @@ * #defines from the assembly-language output. */ +#define COMPILE_OFFSETS #define ASM_OFFSETS_C #include diff --git a/arch/microblaze/kernel/asm-offsets.c b/arch/microblaze/kernel/asm-offsets.c index 104c3ac5f30c..b4b67d58e7f6 100644 --- a/arch/microblaze/kernel/asm-offsets.c +++ b/arch/microblaze/kernel/asm-offsets.c @@ -7,6 +7,7 @@ * License. See the file "COPYING" in the main directory of this archive * for more details. */ +#define COMPILE_OFFSETS #include #include diff --git a/arch/mips/kernel/asm-offsets.c b/arch/mips/kernel/asm-offsets.c index 1e29efcba46e..5debd9a3854a 100644 --- a/arch/mips/kernel/asm-offsets.c +++ b/arch/mips/kernel/asm-offsets.c @@ -9,6 +9,8 @@ * Kevin Kissell, kevink@mips.com and Carsten Langgaard, carstenl@mips.com * Copyright (C) 2000 MIPS Technologies, Inc. */ +#define COMPILE_OFFSETS + #include #include #include diff --git a/arch/nios2/kernel/asm-offsets.c b/arch/nios2/kernel/asm-offsets.c index e3d9b7b6fb48..88190b503ce5 100644 --- a/arch/nios2/kernel/asm-offsets.c +++ b/arch/nios2/kernel/asm-offsets.c @@ -2,6 +2,7 @@ /* * Copyright (C) 2011 Tobias Klauser */ +#define COMPILE_OFFSETS #include #include diff --git a/arch/openrisc/kernel/asm-offsets.c b/arch/openrisc/kernel/asm-offsets.c index 710651d5aaae..3cc826f2216b 100644 --- a/arch/openrisc/kernel/asm-offsets.c +++ b/arch/openrisc/kernel/asm-offsets.c @@ -18,6 +18,7 @@ * compile this file to assembler, and then extract the * #defines from the assembly-language output. */ +#define COMPILE_OFFSETS #include #include diff --git a/arch/parisc/kernel/asm-offsets.c b/arch/parisc/kernel/asm-offsets.c index 757816a7bd4b..9abfe65492c6 100644 --- a/arch/parisc/kernel/asm-offsets.c +++ b/arch/parisc/kernel/asm-offsets.c @@ -13,6 +13,7 @@ * Copyright (C) 2002 Randolph Chung * Copyright (C) 2003 James Bottomley */ +#define COMPILE_OFFSETS #include #include diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c index b3048f6d3822..a4bc80b30410 100644 --- a/arch/powerpc/kernel/asm-offsets.c +++ b/arch/powerpc/kernel/asm-offsets.c @@ -8,6 +8,7 @@ * compile this file to assembler, and then extract the * #defines from the assembly-language output. */ +#define COMPILE_OFFSETS #include #include diff --git a/arch/riscv/kernel/asm-offsets.c b/arch/riscv/kernel/asm-offsets.c index 6e8c0d6feae9..7d42d3b8a32a 100644 --- a/arch/riscv/kernel/asm-offsets.c +++ b/arch/riscv/kernel/asm-offsets.c @@ -3,6 +3,7 @@ * Copyright (C) 2012 Regents of the University of California * Copyright (C) 2017 SiFive */ +#define COMPILE_OFFSETS #include #include diff --git a/arch/s390/kernel/asm-offsets.c b/arch/s390/kernel/asm-offsets.c index 95ecad9c7d7d..a8915663e917 100644 --- a/arch/s390/kernel/asm-offsets.c +++ b/arch/s390/kernel/asm-offsets.c @@ -4,6 +4,7 @@ * This code generates raw asm output which is post-processed to extract * and format the required data. */ +#define COMPILE_OFFSETS #include #include diff --git a/arch/sh/kernel/asm-offsets.c b/arch/sh/kernel/asm-offsets.c index a0322e832845..429b6a763146 100644 --- a/arch/sh/kernel/asm-offsets.c +++ b/arch/sh/kernel/asm-offsets.c @@ -8,6 +8,7 @@ * compile this file to assembler, and then extract the * #defines from the assembly-language output. */ +#define COMPILE_OFFSETS #include #include diff --git a/arch/sparc/kernel/asm-offsets.c b/arch/sparc/kernel/asm-offsets.c index 3d9b9855dce9..6e660bde48dd 100644 --- a/arch/sparc/kernel/asm-offsets.c +++ b/arch/sparc/kernel/asm-offsets.c @@ -10,6 +10,7 @@ * * On sparc, thread_info data is static and TI_XXX offsets are computed by hand. */ +#define COMPILE_OFFSETS #include #include diff --git a/arch/um/kernel/asm-offsets.c b/arch/um/kernel/asm-offsets.c index 1fb12235ab9c..a69873aa697f 100644 --- a/arch/um/kernel/asm-offsets.c +++ b/arch/um/kernel/asm-offsets.c @@ -1 +1,3 @@ +#define COMPILE_OFFSETS + #include diff --git a/arch/xtensa/kernel/asm-offsets.c b/arch/xtensa/kernel/asm-offsets.c index da38de20ae59..cfbced95e944 100644 --- a/arch/xtensa/kernel/asm-offsets.c +++ b/arch/xtensa/kernel/asm-offsets.c @@ -11,6 +11,7 @@ * * Chris Zankel */ +#define COMPILE_OFFSETS #include #include -- 2.50.1 For now, migrate_enable and migrate_disable are global, which makes them become hotspots in some case. Take BPF for example, the function calling to migrate_enable and migrate_disable in BPF trampoline can introduce significant overhead, and following is the 'perf top' of FENTRY's benchmark (./tools/testing/selftests/bpf/bench trig-fentry): 54.63% bpf_prog_2dcccf652aac1793_bench_trigger_fentry [k] bpf_prog_2dcccf652aac1793_bench_trigger_fentry 10.43% [kernel] [k] migrate_enable 10.07% bpf_trampoline_6442517037 [k] bpf_trampoline_6442517037 8.06% [kernel] [k] __bpf_prog_exit_recur 4.11% libc.so.6 [.] syscall 2.15% [kernel] [k] entry_SYSCALL_64 1.48% [kernel] [k] memchr_inv 1.32% [kernel] [k] fput 1.16% [kernel] [k] _copy_to_user 0.73% [kernel] [k] bpf_prog_test_run_raw_tp So in this commit, we make migrate_enable/migrate_disable inline to obtain better performance. The struct rq is defined internally in kernel/sched/sched.h, and the field "nr_pinned" is accessed in migrate_enable/migrate_disable, which makes it hard to make them inline. Alexei Starovoitov suggests to generate the offset of "nr_pinned" in [1], so we can define the migrate_enable/migrate_disable in include/linux/sched.h and access "this_rq()->nr_pinned" with "(void *)this_rq() + RQ_nr_pinned". The offset of "nr_pinned" is generated in include/generated/rq-offsets.h by kernel/sched/rq-offsets.c. Generally speaking, we move the definition of migrate_enable and migrate_disable to include/linux/sched.h from kernel/sched/core.c. The calling to __set_cpus_allowed_ptr() is leaved in ___migrate_enable(). The "struct rq" is not available in include/linux/sched.h, so we can't access the "runqueues" with this_cpu_ptr(), as the compilation will fail in this_cpu_ptr() -> raw_cpu_ptr() -> __verify_pcpu_ptr(): typeof((ptr) + 0) So we introduce the this_rq_raw() and access the runqueues with arch_raw_cpu_ptr/PERCPU_PTR directly. The variable "runqueues" is not visible in the kernel modules, and export it is not a good idea. As Peter Zijlstra advised in [2], we define and export migrate_enable/migrate_disable in kernel/sched/core.c too, and use them for the modules. Before this patch, the performance of BPF FENTRY is: fentry : 113.030 ± 0.149M/s fentry : 112.501 ± 0.187M/s fentry : 112.828 ± 0.267M/s fentry : 115.287 ± 0.241M/s After this patch, the performance of BPF FENTRY increases to: fentry : 143.644 ± 0.670M/s fentry : 149.764 ± 0.362M/s fentry : 149.642 ± 0.156M/s fentry : 145.263 ± 0.221M/s Link: https://lore.kernel.org/bpf/CAADnVQ+5sEDKHdsJY5ZsfGDO_1SEhhQWHrt2SMBG5SYyQ+jt7w@mail.gmail.com/ [1] Link: https://lore.kernel.org/all/20250819123214.GH4067720@noisy.programming.kicks-ass.net/ [2] Signed-off-by: Menglong Dong --- v3: - don't export runqueues, define migrate_enable and migrate_disable in kernel/sched/core.c and use them for kernel modules instead - define the macro this_rq_pinned() - add some comment for this_rq_raw() v2: - use PERCPU_PTR() for this_rq_raw() if !CONFIG_SMP --- Kbuild | 13 ++++- include/linux/preempt.h | 3 -- include/linux/sched.h | 106 ++++++++++++++++++++++++++++++++++++++ kernel/bpf/verifier.c | 1 + kernel/sched/core.c | 63 +++++----------------- kernel/sched/rq-offsets.c | 12 +++++ 6 files changed, 145 insertions(+), 53 deletions(-) create mode 100644 kernel/sched/rq-offsets.c diff --git a/Kbuild b/Kbuild index f327ca86990c..13324b4bbe23 100644 --- a/Kbuild +++ b/Kbuild @@ -34,13 +34,24 @@ arch/$(SRCARCH)/kernel/asm-offsets.s: $(timeconst-file) $(bounds-file) $(offsets-file): arch/$(SRCARCH)/kernel/asm-offsets.s FORCE $(call filechk,offsets,__ASM_OFFSETS_H__) +# Generate rq-offsets.h + +rq-offsets-file := include/generated/rq-offsets.h + +targets += kernel/sched/rq-offsets.s + +kernel/sched/rq-offsets.s: $(offsets-file) + +$(rq-offsets-file): kernel/sched/rq-offsets.s FORCE + $(call filechk,offsets,__RQ_OFFSETS_H__) + # Check for missing system calls quiet_cmd_syscalls = CALL $< cmd_syscalls = $(CONFIG_SHELL) $< $(CC) $(c_flags) $(missing_syscalls_flags) PHONY += missing-syscalls -missing-syscalls: scripts/checksyscalls.sh $(offsets-file) +missing-syscalls: scripts/checksyscalls.sh $(rq-offsets-file) $(call cmd,syscalls) # Check the manual modification of atomic headers diff --git a/include/linux/preempt.h b/include/linux/preempt.h index 1fad1c8a4c76..92237c319035 100644 --- a/include/linux/preempt.h +++ b/include/linux/preempt.h @@ -424,8 +424,6 @@ static inline void preempt_notifier_init(struct preempt_notifier *notifier, * work-conserving schedulers. * */ -extern void migrate_disable(void); -extern void migrate_enable(void); /** * preempt_disable_nested - Disable preemption inside a normally preempt disabled section @@ -471,7 +469,6 @@ static __always_inline void preempt_enable_nested(void) DEFINE_LOCK_GUARD_0(preempt, preempt_disable(), preempt_enable()) DEFINE_LOCK_GUARD_0(preempt_notrace, preempt_disable_notrace(), preempt_enable_notrace()) -DEFINE_LOCK_GUARD_0(migrate, migrate_disable(), migrate_enable()) #ifdef CONFIG_PREEMPT_DYNAMIC diff --git a/include/linux/sched.h b/include/linux/sched.h index f8188b833350..ae73fb70cc05 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -49,6 +49,9 @@ #include #include #include +#ifndef COMPILE_OFFSETS +#include +#endif /* task_struct member predeclarations (sorted alphabetically): */ struct audit_context; @@ -2312,4 +2315,107 @@ static __always_inline void alloc_tag_restore(struct alloc_tag *tag, struct allo #define alloc_tag_restore(_tag, _old) do {} while (0) #endif +#ifndef MODULE +#ifndef COMPILE_OFFSETS + +extern void ___migrate_enable(void); + +struct rq; +DECLARE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues); + +/* The "struct rq" is not available here, so we can't access the + * "runqueues" with this_cpu_ptr(), as the compilation will fail in + * this_cpu_ptr() -> raw_cpu_ptr() -> __verify_pcpu_ptr(): + * typeof((ptr) + 0) + * + * So use arch_raw_cpu_ptr()/PERCPU_PTR() directly here. + */ +#ifdef CONFIG_SMP +#define this_rq_raw() arch_raw_cpu_ptr(&runqueues) +#else +#define this_rq_raw() PERCPU_PTR(&runqueues) +#endif +#define this_rq_pinned() (*(unsigned int *)((void *)this_rq_raw() + RQ_nr_pinned)) + +static inline void __migrate_enable(void) +{ + struct task_struct *p = current; + +#ifdef CONFIG_DEBUG_PREEMPT + /* + * Check both overflow from migrate_disable() and superfluous + * migrate_enable(). + */ + if (WARN_ON_ONCE((s16)p->migration_disabled <= 0)) + return; +#endif + + if (p->migration_disabled > 1) { + p->migration_disabled--; + return; + } + + /* + * Ensure stop_task runs either before or after this, and that + * __set_cpus_allowed_ptr(SCA_MIGRATE_ENABLE) doesn't schedule(). + */ + guard(preempt)(); + if (unlikely(p->cpus_ptr != &p->cpus_mask)) + ___migrate_enable(); + /* + * Mustn't clear migration_disabled() until cpus_ptr points back at the + * regular cpus_mask, otherwise things that race (eg. + * select_fallback_rq) get confused. + */ + barrier(); + p->migration_disabled = 0; + this_rq_pinned()--; +} + +static inline void __migrate_disable(void) +{ + struct task_struct *p = current; + + if (p->migration_disabled) { +#ifdef CONFIG_DEBUG_PREEMPT + /* + *Warn about overflow half-way through the range. + */ + WARN_ON_ONCE((s16)p->migration_disabled < 0); +#endif + p->migration_disabled++; + return; + } + + guard(preempt)(); + this_rq_pinned()++; + p->migration_disabled = 1; +} +#else /* !COMPILE_OFFSETS */ +static inline void __migrate_disable(void) { } +static inline void __migrate_enable(void) { } +#endif /* !COMPILE_OFFSETS */ + +#ifndef CREATE_MIGRATE_DISABLE +static inline void migrate_disable(void) +{ + __migrate_disable(); +} + +static inline void migrate_enable(void) +{ + __migrate_enable(); +} +#else /* CREATE_MIGRATE_DISABLE */ +extern void migrate_disable(void); +extern void migrate_enable(void); +#endif /* CREATE_MIGRATE_DISABLE */ + +#else /* MODULE */ +extern void migrate_disable(void); +extern void migrate_enable(void); +#endif /* MODULE */ + +DEFINE_LOCK_GUARD_0(migrate, migrate_disable(), migrate_enable()) + #endif diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index c4f69a9e9af6..de9078a9df3a 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -23855,6 +23855,7 @@ int bpf_check_attach_target(struct bpf_verifier_log *log, BTF_SET_START(btf_id_deny) BTF_ID_UNUSED #ifdef CONFIG_SMP +BTF_ID(func, ___migrate_enable) BTF_ID(func, migrate_disable) BTF_ID(func, migrate_enable) #endif diff --git a/kernel/sched/core.c b/kernel/sched/core.c index be00629f0ba4..58164a69449d 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7,6 +7,8 @@ * Copyright (C) 1991-2002 Linus Torvalds * Copyright (C) 1998-2024 Ingo Molnar, Red Hat */ +#define CREATE_MIGRATE_DISABLE +#include #include #include #include @@ -2381,28 +2383,7 @@ static void migrate_disable_switch(struct rq *rq, struct task_struct *p) __do_set_cpus_allowed(p, &ac); } -void migrate_disable(void) -{ - struct task_struct *p = current; - - if (p->migration_disabled) { -#ifdef CONFIG_DEBUG_PREEMPT - /* - *Warn about overflow half-way through the range. - */ - WARN_ON_ONCE((s16)p->migration_disabled < 0); -#endif - p->migration_disabled++; - return; - } - - guard(preempt)(); - this_rq()->nr_pinned++; - p->migration_disabled = 1; -} -EXPORT_SYMBOL_GPL(migrate_disable); - -void migrate_enable(void) +void ___migrate_enable(void) { struct task_struct *p = current; struct affinity_context ac = { @@ -2410,35 +2391,19 @@ void migrate_enable(void) .flags = SCA_MIGRATE_ENABLE, }; -#ifdef CONFIG_DEBUG_PREEMPT - /* - * Check both overflow from migrate_disable() and superfluous - * migrate_enable(). - */ - if (WARN_ON_ONCE((s16)p->migration_disabled <= 0)) - return; -#endif + __set_cpus_allowed_ptr(p, &ac); +} +EXPORT_SYMBOL_GPL(___migrate_enable); - if (p->migration_disabled > 1) { - p->migration_disabled--; - return; - } +void migrate_disable(void) +{ + __migrate_disable(); +} +EXPORT_SYMBOL_GPL(migrate_disable); - /* - * Ensure stop_task runs either before or after this, and that - * __set_cpus_allowed_ptr(SCA_MIGRATE_ENABLE) doesn't schedule(). - */ - guard(preempt)(); - if (p->cpus_ptr != &p->cpus_mask) - __set_cpus_allowed_ptr(p, &ac); - /* - * Mustn't clear migration_disabled() until cpus_ptr points back at the - * regular cpus_mask, otherwise things that race (eg. - * select_fallback_rq) get confused. - */ - barrier(); - p->migration_disabled = 0; - this_rq()->nr_pinned--; +void migrate_enable(void) +{ + __migrate_enable(); } EXPORT_SYMBOL_GPL(migrate_enable); diff --git a/kernel/sched/rq-offsets.c b/kernel/sched/rq-offsets.c new file mode 100644 index 000000000000..a23747bbe25b --- /dev/null +++ b/kernel/sched/rq-offsets.c @@ -0,0 +1,12 @@ +// SPDX-License-Identifier: GPL-2.0 +#define COMPILE_OFFSETS +#include +#include +#include "sched.h" + +int main(void) +{ + DEFINE(RQ_nr_pinned, offsetof(struct rq, nr_pinned)); + + return 0; +} -- 2.50.1 There are some typos in the comments of migrate in include/linux/preempt.h: elegible -> eligible it's -> its migirate_disable -> migrate_disable abritrary -> arbitrary Just fix them. Signed-off-by: Menglong Dong --- include/linux/preempt.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/include/linux/preempt.h b/include/linux/preempt.h index 92237c319035..102202185d7a 100644 --- a/include/linux/preempt.h +++ b/include/linux/preempt.h @@ -372,7 +372,7 @@ static inline void preempt_notifier_init(struct preempt_notifier *notifier, /* * Migrate-Disable and why it is undesired. * - * When a preempted task becomes elegible to run under the ideal model (IOW it + * When a preempted task becomes eligible to run under the ideal model (IOW it * becomes one of the M highest priority tasks), it might still have to wait * for the preemptee's migrate_disable() section to complete. Thereby suffering * a reduction in bandwidth in the exact duration of the migrate_disable() @@ -387,7 +387,7 @@ static inline void preempt_notifier_init(struct preempt_notifier *notifier, * - a lower priority tasks; which under preempt_disable() could've instantly * migrated away when another CPU becomes available, is now constrained * by the ability to push the higher priority task away, which might itself be - * in a migrate_disable() section, reducing it's available bandwidth. + * in a migrate_disable() section, reducing its available bandwidth. * * IOW it trades latency / moves the interference term, but it stays in the * system, and as long as it remains unbounded, the system is not fully @@ -399,7 +399,7 @@ static inline void preempt_notifier_init(struct preempt_notifier *notifier, * PREEMPT_RT breaks a number of assumptions traditionally held. By forcing a * number of primitives into becoming preemptible, they would also allow * migration. This turns out to break a bunch of per-cpu usage. To this end, - * all these primitives employ migirate_disable() to restore this implicit + * all these primitives employ migrate_disable() to restore this implicit * assumption. * * This is a 'temporary' work-around at best. The correct solution is getting @@ -407,7 +407,7 @@ static inline void preempt_notifier_init(struct preempt_notifier *notifier, * per-cpu locking or short preempt-disable regions. * * The end goal must be to get rid of migrate_disable(), alternatively we need - * a schedulability theory that does not depend on abritrary migration. + * a schedulability theory that does not depend on arbitrary migration. * * * Notes on the implementation. -- 2.50.1