From: Michal Hocko mhocko@kernel.org
mainline inclusion from mainline-5.12-rc1 commit 6ef869e0647439af0fc28dde162d33320d4e1dd7 category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I410UT CVE: NA Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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Preemption mode selection is currently hardcoded on Kconfig choices. Introduce a dedicated option to tune preemption flavour at boot time,
This will be only available on architectures efficiently supporting static calls in order not to tempt with the feature against additional overhead that might be prohibitive or undesirable.
CONFIG_PREEMPT_DYNAMIC is automatically selected by CONFIG_PREEMPT if the architecture provides the necessary support (CONFIG_STATIC_CALL_INLINE, CONFIG_GENERIC_ENTRY, and provide with __preempt_schedule_function() / __preempt_schedule_notrace_function()).
Suggested-by: Peter Zijlstra peterz@infradead.org Signed-off-by: Michal Hocko mhocko@suse.com Signed-off-by: Frederic Weisbecker frederic@kernel.org [peterz: relax requirement to HAVE_STATIC_CALL] Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Signed-off-by: Ingo Molnar mingo@kernel.org Link: https://lkml.kernel.org/r/20210118141223.123667-5-frederic@kernel.org Signed-off-by: Ma Junhai majunhai2@huawei.com Reviewed-by: Chen Hui judy.chenhui@huawei.com Signed-off-by: Zheng Zengkai zhengzengkai@huawei.com --- .../admin-guide/kernel-parameters.txt | 7 +++++++ arch/Kconfig | 9 +++++++++ arch/x86/Kconfig | 1 + kernel/Kconfig.preempt | 19 +++++++++++++++++++ 4 files changed, 36 insertions(+)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index c125a678fcf3..e732fe5d4e42 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -3997,6 +3997,13 @@ Format: {"off"} Disable Hardware Transactional Memory
+ preempt= [KNL] + Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC + none - Limited to cond_resched() calls + voluntary - Limited to cond_resched() and might_sleep() calls + full - Any section that isn't explicitly preempt disabled + can be preempted anytime. + print-fatal-signals= [KNL] debug: print fatal signals
diff --git a/arch/Kconfig b/arch/Kconfig index 3f9f9739655f..f2d65d38f119 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -1082,6 +1082,15 @@ config HAVE_STATIC_CALL_INLINE bool depends on HAVE_STATIC_CALL
+config HAVE_PREEMPT_DYNAMIC + bool + depends on HAVE_STATIC_CALL + depends on GENERIC_ENTRY + help + Select this if the architecture support boot time preempt setting + on top of static calls. It is strongly advised to support inline + static call to avoid any overhead. + config ARCH_WANT_LD_ORPHAN_WARN bool help diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 9bf0136e8bff..af7123b5b493 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -223,6 +223,7 @@ config X86 select HAVE_STACK_VALIDATION if X86_64 select HAVE_STATIC_CALL select HAVE_STATIC_CALL_INLINE if HAVE_STACK_VALIDATION + select HAVE_PREEMPT_DYNAMIC select HAVE_RSEQ select HAVE_SYSCALL_TRACEPOINTS select HAVE_UNSTABLE_SCHED_CLOCK diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt index bf82259cff96..416017301660 100644 --- a/kernel/Kconfig.preempt +++ b/kernel/Kconfig.preempt @@ -40,6 +40,7 @@ config PREEMPT depends on !ARCH_NO_PREEMPT select PREEMPTION select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK + select PREEMPT_DYNAMIC if HAVE_PREEMPT_DYNAMIC help This option reduces the latency of the kernel by making all kernel code (that is not executing in a critical section) @@ -80,3 +81,21 @@ config PREEMPT_COUNT config PREEMPTION bool select PREEMPT_COUNT + +config PREEMPT_DYNAMIC + bool + help + This option allows to define the preemption model on the kernel + command line parameter and thus override the default preemption + model defined during compile time. + + The feature is primarily interesting for Linux distributions which + provide a pre-built kernel binary to reduce the number of kernel + flavors they offer while still offering different usecases. + + The runtime overhead is negligible with HAVE_STATIC_CALL_INLINE enabled + but if runtime patching is not available for the specific architecture + then the potential overhead should be considered. + + Interesting if you want the same pre-built kernel should be used for + both Server and Desktop workloads.