From 68efde1ad11dabda38df2084db0c508450246492 Mon Sep 17 00:00:00 2001 From: John Dias Date: Wed, 5 Oct 2016 15:11:40 -0700 Subject: [PATCH] sched: avoid migrating when softint on tgt cpu should be short The scheduling change (bug 31501544) to avoid putting RT threads on cores that are handling softint's was catching cases where there was no reason to believe the softint would take a long time, resulting in unnecessary migration overhead. This patch reduces the migration to cases where the core has a softint that is actually likely to take a long time, as opposed to the RCU, SCHED, and TIMER softints that are rather quick. Bug: 31752786 Change-Id: Ib4e179f1e15c736b2fdba31070494e357e9fbbe2 Git-commit: ce05770bd37b8065b61ef650108ecef2b97b148b Git-repo: https://android.googlesource.com/kernel/msm [pkondeti@codeaurora.org: resolved minor merge conflicts] Signed-off-by: Pavankumar Kondeti [satyap@codeaurora.org: resolve trivial merge conflicts] Signed-off-by: Satya Durga Srinivasu Prabhala --- include/linux/interrupt.h | 7 +++++++ kernel/sched/rt.c | 12 ++++++++---- kernel/softirq.c | 9 +++++++++ 3 files changed, 24 insertions(+), 4 deletions(-) diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h index 89fc59dab57d..2ccad949658b 100644 --- a/include/linux/interrupt.h +++ b/include/linux/interrupt.h @@ -528,6 +528,12 @@ enum }; #define SOFTIRQ_STOP_IDLE_MASK (~(1 << RCU_SOFTIRQ)) +/* Softirq's where the handling might be long: */ +#define LONG_SOFTIRQ_MASK ((1 << NET_TX_SOFTIRQ) | \ + (1 << NET_RX_SOFTIRQ) | \ + (1 << BLOCK_SOFTIRQ) | \ + (1 << IRQ_POLL_SOFTIRQ) | \ + (1 << TASKLET_SOFTIRQ)) /* map softirq index to softirq name. update 'softirq_to_name' in * kernel/softirq.c when adding a new softirq. @@ -563,6 +569,7 @@ extern void raise_softirq_irqoff(unsigned int nr); extern void raise_softirq(unsigned int nr); DECLARE_PER_CPU(struct task_struct *, ksoftirqd); +DECLARE_PER_CPU(__u32, active_softirqs); static inline struct task_struct *this_cpu_ksoftirqd(void) { diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index bedb98fd186d..3a9a757bfe03 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -1464,16 +1464,20 @@ static int find_lowest_rq(struct task_struct *task); /* * Return whether the task on the given cpu is currently non-preemptible - * while handling a softirq or is likely to block preemptions soon because - * it is a ksoftirq thread. + * while handling a potentially long softint, or if the task is likely + * to block preemptions soon because it is a ksoftirq thread that is + * handling slow softints. */ bool task_may_not_preempt(struct task_struct *task, int cpu) { + __u32 softirqs = per_cpu(active_softirqs, cpu) | + __IRQ_STAT(cpu, __softirq_pending); struct task_struct *cpu_ksoftirqd = per_cpu(ksoftirqd, cpu); - return (task_thread_info(task)->preempt_count & SOFTIRQ_MASK) || - task == cpu_ksoftirqd; + return ((softirqs & LONG_SOFTIRQ_MASK) && + (task == cpu_ksoftirqd || + task_thread_info(task)->preempt_count & SOFTIRQ_MASK)); } static int diff --git a/kernel/softirq.c b/kernel/softirq.c index 0427a86743a4..a459e8f0f1b0 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -56,6 +56,13 @@ static struct softirq_action softirq_vec[NR_SOFTIRQS] __cacheline_aligned_in_smp DEFINE_PER_CPU(struct task_struct *, ksoftirqd); +/* + * active_softirqs -- per cpu, a mask of softirqs that are being handled, + * with the expectation that approximate answers are acceptable and therefore + * no synchronization. + */ +DEFINE_PER_CPU(__u32, active_softirqs); + const char * const softirq_to_name[NR_SOFTIRQS] = { "HI", "TIMER", "NET_TX", "NET_RX", "BLOCK", "IRQ_POLL", "TASKLET", "SCHED", "HRTIMER", "RCU" @@ -272,6 +279,7 @@ asmlinkage __visible void __softirq_entry __do_softirq(void) restart: /* Reset the pending bitmask before enabling irqs */ set_softirq_pending(0); + __this_cpu_write(active_softirqs, pending); local_irq_enable(); @@ -301,6 +309,7 @@ asmlinkage __visible void __softirq_entry __do_softirq(void) pending >>= softirq_bit; } + __this_cpu_write(active_softirqs, 0); if (__this_cpu_read(ksoftirqd) == current) rcu_softirq_qs(); local_irq_disable();