From 9cc5b8656892a72438ee7deb5e80f5be47643b8b Mon Sep 17 00:00:00 2001 From: Marcelo Tosatti Date: Wed, 27 May 2020 16:29:09 +0200 Subject: [PATCH] isolcpus: Affine unbound kernel threads to housekeeping cpus This is a kernel enhancement that configures the cpu affinity of kernel threads via kernel boot option nohz_full=. When this option is specified, the cpumask is immediately applied upon kthread launch. This does not affect kernel threads that specify cpu and node. This allows CPU isolation (that is not allowing certain threads to execute on certain CPUs) without using the isolcpus=domain parameter, making it possible to enable load balancing on such CPUs during runtime (see kernel-parameters.txt). Note-1: this is based off on Wind River's patch at https://github.com/starlingx-staging/stx-integ/blob/master/kernel/kernel-std/centos/patches/affine-compute-kernel-threads.patch Difference being that this patch is limited to modifying kernel thread cpumask. Behaviour of other threads can be controlled via cgroups or sched_setaffinity. Note-2: Wind River's patch was based off Christoph Lameter's patch at https://lwn.net/Articles/565932/ with the only difference being the kernel parameter changed from kthread to kthread_cpus. Signed-off-by: Frederic Weisbecker Signed-off-by: Marcelo Tosatti Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20200527142909.23372-3-frederic@kernel.org --- include/linux/sched/isolation.h | 1 + kernel/kthread.c | 6 ++++-- kernel/sched/isolation.c | 3 ++- 3 files changed, 7 insertions(+), 3 deletions(-) diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h index 0fbcbacd1b29..cc9f393e2a70 100644 --- a/include/linux/sched/isolation.h +++ b/include/linux/sched/isolation.h @@ -14,6 +14,7 @@ enum hk_flags { HK_FLAG_DOMAIN = (1 << 5), HK_FLAG_WQ = (1 << 6), HK_FLAG_MANAGED_IRQ = (1 << 7), + HK_FLAG_KTHREAD = (1 << 8), }; #ifdef CONFIG_CPU_ISOLATION diff --git a/kernel/kthread.c b/kernel/kthread.c index b86d37cda109..032b610912b0 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -27,6 +27,7 @@ #include #include #include +#include #include @@ -383,7 +384,8 @@ struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data), * The kernel thread should not inherit these properties. */ sched_setscheduler_nocheck(task, SCHED_NORMAL, ¶m); - set_cpus_allowed_ptr(task, cpu_possible_mask); + set_cpus_allowed_ptr(task, + housekeeping_cpumask(HK_FLAG_KTHREAD)); } kfree(create); return task; @@ -608,7 +610,7 @@ int kthreadd(void *unused) /* Setup a clean context for our children to inherit. */ set_task_comm(tsk, "kthreadd"); ignore_signals(tsk); - set_cpus_allowed_ptr(tsk, cpu_possible_mask); + set_cpus_allowed_ptr(tsk, housekeeping_cpumask(HK_FLAG_KTHREAD)); set_mems_allowed(node_states[N_MEMORY]); current->flags |= PF_NOFREEZE; diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c index 808244f3ddd9..5a6ea03f9882 100644 --- a/kernel/sched/isolation.c +++ b/kernel/sched/isolation.c @@ -140,7 +140,8 @@ static int __init housekeeping_nohz_full_setup(char *str) { unsigned int flags; - flags = HK_FLAG_TICK | HK_FLAG_WQ | HK_FLAG_TIMER | HK_FLAG_RCU | HK_FLAG_MISC; + flags = HK_FLAG_TICK | HK_FLAG_WQ | HK_FLAG_TIMER | HK_FLAG_RCU | + HK_FLAG_MISC | HK_FLAG_KTHREAD; return housekeeping_setup(str, flags); }