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ANDROID: sched: avoid migrating when softint on tgt cpu should be short

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The scheduling change 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
Bug: 168521633
Change-Id: Ib4e179f1e15c736b2fdba31070494e357e9fbbe2
Signed-off-by: John Dias <joaodias@google.com>
[elavila: Amend commit text for AOSP, port to mainline]
Signed-off-by: J. Avila <elavila@google.com>
This commit is contained in:
John Dias 2016-10-05 15:11:40 -07:00 committed by J. Avila
parent 3adfd8e344
commit 8d19443b0b
3 changed files with 25 additions and 4 deletions
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7
include/linux/interrupt.h
View File

@ -542,6 +542,12 @@ 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.
@ -577,6 +583,7 @@ 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)
{

13
kernel/sched/rt.c
View File

@ -1439,15 +1439,20 @@ static int find_lowest_rq(struct task_struct *task);
#ifdef CONFIG_RT_SOFTINT_OPTIMIZATION
/*
* 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));
}
#endif /* CONFIG_RT_SOFTINT_OPTIMIZATION */

9
kernel/softirq.c
View File

@ -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"
@ -278,6 +285,7 @@ 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();
@ -307,6 +315,7 @@ 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();