Messages in this thread Patch in this message | | | From | "Joel Fernandes (Google)" <> | Subject | [RFC 1/2] x86/bugs: Disable coresched on hardware that does not need it | Date | Wed, 11 Nov 2020 16:10:10 -0500 |
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Some hardware such as certain AMD variants don't have cross-HT MDS/L1TF issues. Detect this and don't enable core scheduling as it can needlessly slow the device done.
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> --- arch/x86/kernel/cpu/bugs.c | 8 ++++++++ kernel/sched/core.c | 7 +++++++ kernel/sched/sched.h | 5 +++++ 3 files changed, 20 insertions(+)
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index dece79e4d1e9..0e6e61e49b23 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -152,6 +152,14 @@ void __init check_bugs(void) #endif } +/* + * Do not need core scheduling if CPU does not have MDS/L1TF vulnerability. + */ +int arch_allow_core_sched(void) +{ + return boot_cpu_has_bug(X86_BUG_MDS) || boot_cpu_has_bug(X86_BUG_L1TF); +} + void x86_virt_spec_ctrl(u64 guest_spec_ctrl, u64 guest_virt_spec_ctrl, bool setguest) { diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 64c559192634..c6158b4959fe 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -319,6 +319,13 @@ static void __sched_core_enable(void) for_each_online_cpu(cpu) BUG_ON(!sched_core_empty(cpu_rq(cpu))); + /* + * Some architectures may not want coresched. (ex, AMD does not have + * MDS/L1TF issues so it wants SMT completely on). + */ + if (!arch_allow_core_sched()) + return; + static_branch_enable(&__sched_core_enabled); stop_machine(__sched_core_stopper, (void *)true, NULL); diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 3cf08c77b678..a1b39764a6ed 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1203,6 +1203,11 @@ int cpu_core_tag_color_write_u64(struct cgroup_subsys_state *css, bool cfs_prio_less(struct task_struct *a, struct task_struct *b, bool fi); +int __weak arch_allow_core_sched(void) +{ + return true; +} + #else /* !CONFIG_SCHED_CORE */ static inline bool sched_core_enqueued(struct task_struct *task) { return false; } -- 2.29.2.222.g5d2a92d10f8-goog
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