3.14.23-rt20 - softirq: resurrect softirq threads

From: Mike Galbraith
Date: Sun Nov 02 2014 - 02:31:59 EST

(sirqs suck, this makes them suck less for some boxen/loads)

Subject: softirq: resurrect softirq threads
From: Mike Galbraith <mgalbraith@xxxxxxx>
Date: Mon Jan 6 08:42:11 CET 2014

Some loads cannot tolerate the jitter induced by all softirqs being processed
at the same priority. Let the user prioritize them again.

Signed-off-by: Mike Galbraith <mgalbraith@xxxxxxx>
---
Documentation/kernel-parameters.txt | 3
include/linux/interrupt.h | 9 -
include/linux/sched.h | 6 +
kernel/sched/cputime.c | 4
kernel/softirq.c | 182 +++++++++++++++++++++++++++++++-----
5 files changed, 173 insertions(+), 31 deletions(-)

--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3187,6 +3187,9 @@ bytes respectively. Such letter suffixes
Force threading of all interrupt handlers except those
marked explicitly IRQF_NO_THREAD.

+ threadsirqs [KNL]
+ Enable or disable threading of all softirqs for -rt.
+
tmem [KNL,XEN]
Enable the Transcendent memory driver if built-in.

--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -425,6 +425,7 @@ struct softirq_action
asmlinkage void do_softirq(void);
asmlinkage void __do_softirq(void);
static inline void thread_do_softirq(void) { do_softirq(); }
+#define NR_SOFTIRQ_THREADS 1
#ifdef __ARCH_HAS_DO_SOFTIRQ
void do_softirq_own_stack(void);
#else
@@ -435,6 +436,7 @@ static inline void do_softirq_own_stack(
#endif
#else
extern void thread_do_softirq(void);
+#define NR_SOFTIRQ_THREADS NR_SOFTIRQS
#endif

extern void open_softirq(int nr, void (*action)(struct softirq_action *));
@@ -445,12 +447,7 @@ extern void raise_softirq_irqoff(unsigne
extern void raise_softirq(unsigned int nr);
extern void softirq_check_pending_idle(void);

-DECLARE_PER_CPU(struct task_struct *, ksoftirqd);
-
-static inline struct task_struct *this_cpu_ksoftirqd(void)
-{
- return this_cpu_read(ksoftirqd);
-}
+DECLARE_PER_CPU(struct task_struct * [NR_SOFTIRQ_THREADS], ksoftirqd);

/* Tasklets --- multithreaded analogue of BHs.

--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1263,6 +1263,7 @@ struct task_struct {
/* Revert to default priority/policy when forking */
unsigned sched_reset_on_fork:1;
unsigned sched_contributes_to_load:1;
+ unsigned sched_is_softirqd:1;

pid_t pid;
pid_t tgid;
@@ -1678,6 +1679,11 @@ static inline struct pid *task_tgid(stru
return task->group_leader->pids[PIDTYPE_PID].pid;
}

+static inline bool task_is_softirqd(struct task_struct *task)
+{
+ return task->sched_is_softirqd;
+}
+
/*
* Without tasklist or rcu lock it is not safe to dereference
* the result of task_pgrp/task_session even if task == current,
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -68,7 +68,7 @@ void irqtime_account_irq(struct task_str
*/
if (hardirq_count())
__this_cpu_add(cpu_hardirq_time, delta);
- else if (in_serving_softirq() && curr != this_cpu_ksoftirqd())
+ else if (in_serving_softirq() && !task_is_softirqd(curr))
__this_cpu_add(cpu_softirq_time, delta);

irq_time_write_end();
@@ -342,7 +342,7 @@ static void irqtime_account_process_tick
cpustat[CPUTIME_IRQ] += cputime;
} else if (irqtime_account_si_update()) {
cpustat[CPUTIME_SOFTIRQ] += cputime;
- } else if (this_cpu_ksoftirqd() == p) {
+ } else if (task_is_softirqd(p)) {
/*
* ksoftirqd time do not get accounted in cpu_softirq_time.
* So, we have to handle it separately here.
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -56,7 +56,14 @@ EXPORT_SYMBOL(irq_stat);

static struct softirq_action softirq_vec[NR_SOFTIRQS] __cacheline_aligned_in_smp;

-DEFINE_PER_CPU(struct task_struct *, ksoftirqd);
+DEFINE_PER_CPU(struct task_struct * [NR_SOFTIRQ_THREADS], ksoftirqd);
+
+static unsigned int __read_mostly threadsirqs;
+
+static struct task_struct *__this_cpu_ksoftirqd(int nr)
+{
+ return __this_cpu_read(ksoftirqd[nr && threadsirqs ? nr : 0]);
+}

const char * const softirq_to_name[NR_SOFTIRQS] = {
"HI", "TIMER", "NET_TX", "NET_RX", "BLOCK", "BLOCK_IOPOLL",
@@ -161,10 +168,10 @@ static inline void softirq_clr_runner(un
* to the pending events, so lets the scheduler to balance
* the softirq load for us.
*/
-static void wakeup_softirqd(void)
+static void wakeup_softirqd(int nr)
{
/* Interrupts are disabled: no need to stop preemption */
- struct task_struct *tsk = __this_cpu_read(ksoftirqd);
+ struct task_struct *tsk = __this_cpu_ksoftirqd(nr);

if (tsk && tsk->state != TASK_RUNNING)
wake_up_process(tsk);
@@ -413,7 +420,7 @@ asmlinkage void __do_softirq(void)
--max_restart)
goto restart;

- wakeup_softirqd();
+ wakeup_softirqd(0);
}

lockdep_softirq_end(in_hardirq);
@@ -458,7 +465,7 @@ void raise_softirq_irqoff(unsigned int n
* schedule the softirq soon.
*/
if (!in_interrupt())
- wakeup_softirqd();
+ wakeup_softirqd(0);
}

void __raise_softirq_irqoff(unsigned int nr)
@@ -469,8 +476,18 @@ void __raise_softirq_irqoff(unsigned int

static inline void local_bh_disable_nort(void) { local_bh_disable(); }
static inline void _local_bh_enable_nort(void) { _local_bh_enable(); }
-static void ksoftirqd_set_sched_params(unsigned int cpu) { }
-static void ksoftirqd_clr_sched_params(unsigned int cpu, bool online) { }
+static void ksoftirqd_set_sched_params(unsigned int cpu)
+{
+ local_irq_disable();
+ current->sched_is_softirqd = 1;
+ local_irq_enable();
+}
+static void ksoftirqd_clr_sched_params(unsigned int cpu, bool online)
+{
+ local_irq_disable();
+ current->sched_is_softirqd = 0;
+ local_irq_enable();
+}

#else /* !PREEMPT_RT_FULL */

@@ -656,15 +673,15 @@ static void do_raise_softirq_irqoff(unsi

if (!in_irq() && current->softirq_nestcnt)
current->softirqs_raised |= (1U << nr);
- else if (__this_cpu_read(ksoftirqd))
- __this_cpu_read(ksoftirqd)->softirqs_raised |= (1U << nr);
+ else if (__this_cpu_ksoftirqd(nr))
+ __this_cpu_ksoftirqd(nr)->softirqs_raised |= (1U << nr);
}

void __raise_softirq_irqoff(unsigned int nr)
{
do_raise_softirq_irqoff(nr);
if (!in_irq() && !current->softirq_nestcnt)
- wakeup_softirqd();
+ wakeup_softirqd(nr);
}

/*
@@ -691,7 +708,7 @@ void raise_softirq_irqoff(unsigned int n
*
*/
if (!current->softirq_nestcnt)
- wakeup_softirqd();
+ wakeup_softirqd(nr);
}

static inline int ksoftirqd_softirq_pending(void)
@@ -709,6 +726,7 @@ static inline void ksoftirqd_set_sched_p
sched_setscheduler(current, SCHED_FIFO, &param);
/* Take over all pending softirqs when starting */
local_irq_disable();
+ current->sched_is_softirqd = 1;
current->softirqs_raised = local_softirq_pending();
local_irq_enable();
}
@@ -717,9 +735,26 @@ static inline void ksoftirqd_clr_sched_p
{
struct sched_param param = { .sched_priority = 0 };

+ local_irq_disable();
+ current->sched_is_softirqd = 0;
+ current->softirqs_raised = 0;
+ local_irq_enable();
sched_setscheduler(current, SCHED_NORMAL, &param);
}

+static int __init threadsoftirqs(char *str)
+{
+ int thread = 0;
+
+ if (!get_option(&str, &thread))
+ thread = 1;
+
+ threadsirqs = !!thread;
+
+ return 0;
+}
+
+early_param("threadsirqs", threadsoftirqs);
#endif /* PREEMPT_RT_FULL */
/*
* Enter an interrupt context.
@@ -760,15 +795,25 @@ static inline void invoke_softirq(void)
do_softirq_own_stack();
#endif
} else {
- wakeup_softirqd();
+ wakeup_softirqd(0);
}
#else /* PREEMPT_RT_FULL */
+ struct task_struct *tsk;
unsigned long flags;
+ u32 pending, nr;

local_irq_save(flags);
- if (__this_cpu_read(ksoftirqd) &&
- __this_cpu_read(ksoftirqd)->softirqs_raised)
- wakeup_softirqd();
+ pending = local_softirq_pending();
+
+ while (pending) {
+ nr = __ffs(pending);
+ tsk = __this_cpu_ksoftirqd(nr);
+ if (tsk && tsk->softirqs_raised)
+ wakeup_softirqd(nr);
+ if (!threadsirqs)
+ break;
+ pending &= ~(1U << nr);
+ }
local_irq_restore(flags);
#endif
}
@@ -1201,20 +1246,111 @@ static struct notifier_block cpu_nfb = {
.notifier_call = cpu_callback
};

-static struct smp_hotplug_thread softirq_threads = {
- .store = &ksoftirqd,
- .setup = ksoftirqd_set_sched_params,
- .cleanup = ksoftirqd_clr_sched_params,
- .thread_should_run = ksoftirqd_should_run,
- .thread_fn = run_ksoftirqd,
- .thread_comm = "ksoftirqd/%u",
+static struct smp_hotplug_thread softirq_threads[] = {
+ {
+ .store = &ksoftirqd[0],
+ .setup = ksoftirqd_set_sched_params,
+ .cleanup = ksoftirqd_clr_sched_params,
+ .thread_should_run = ksoftirqd_should_run,
+ .thread_fn = run_ksoftirqd,
+ .thread_comm = "ksoftirqd/%u",
+ },
+#ifdef CONFIG_PREEMPT_RT_FULL
+ {
+ .store = &ksoftirqd[HI_SOFTIRQ],
+ .setup = ksoftirqd_set_sched_params,
+ .cleanup = ksoftirqd_clr_sched_params,
+ .thread_should_run = ksoftirqd_should_run,
+ .thread_fn = run_ksoftirqd,
+ .thread_comm = "sirq-high/%u",
+ },
+ {
+ .store = &ksoftirqd[TIMER_SOFTIRQ],
+ .setup = ksoftirqd_set_sched_params,
+ .cleanup = ksoftirqd_clr_sched_params,
+ .thread_should_run = ksoftirqd_should_run,
+ .thread_fn = run_ksoftirqd,
+ .thread_comm = "sirq-timer/%u",
+ },
+ {
+ .store = &ksoftirqd[NET_TX_SOFTIRQ],
+ .setup = ksoftirqd_set_sched_params,
+ .cleanup = ksoftirqd_clr_sched_params,
+ .thread_should_run = ksoftirqd_should_run,
+ .thread_fn = run_ksoftirqd,
+ .thread_comm = "sirq-net-tx/%u",
+ },
+ {
+ .store = &ksoftirqd[NET_RX_SOFTIRQ],
+ .setup = ksoftirqd_set_sched_params,
+ .cleanup = ksoftirqd_clr_sched_params,
+ .thread_should_run = ksoftirqd_should_run,
+ .thread_fn = run_ksoftirqd,
+ .thread_comm = "sirq-net-rx/%u",
+ },
+ {
+ .store = &ksoftirqd[BLOCK_SOFTIRQ],
+ .setup = ksoftirqd_set_sched_params,
+ .cleanup = ksoftirqd_clr_sched_params,
+ .thread_should_run = ksoftirqd_should_run,
+ .thread_fn = run_ksoftirqd,
+ .thread_comm = "sirq-blk/%u",
+ },
+ {
+ .store = &ksoftirqd[BLOCK_IOPOLL_SOFTIRQ],
+ .setup = ksoftirqd_set_sched_params,
+ .cleanup = ksoftirqd_clr_sched_params,
+ .thread_should_run = ksoftirqd_should_run,
+ .thread_fn = run_ksoftirqd,
+ .thread_comm = "sirq-blk-pol/%u",
+ },
+ {
+ .store = &ksoftirqd[TASKLET_SOFTIRQ],
+ .setup = ksoftirqd_set_sched_params,
+ .cleanup = ksoftirqd_clr_sched_params,
+ .thread_should_run = ksoftirqd_should_run,
+ .thread_fn = run_ksoftirqd,
+ .thread_comm = "sirq-tasklet/%u",
+ },
+ {
+ .store = &ksoftirqd[SCHED_SOFTIRQ],
+ .setup = ksoftirqd_set_sched_params,
+ .cleanup = ksoftirqd_clr_sched_params,
+ .thread_should_run = ksoftirqd_should_run,
+ .thread_fn = run_ksoftirqd,
+ .thread_comm = "sirq-sched/%u",
+ },
+ {
+ .store = &ksoftirqd[HRTIMER_SOFTIRQ],
+ .setup = ksoftirqd_set_sched_params,
+ .cleanup = ksoftirqd_clr_sched_params,
+ .thread_should_run = ksoftirqd_should_run,
+ .thread_fn = run_ksoftirqd,
+ .thread_comm = "sirq-hrtimer/%u",
+ },
+ {
+ .store = &ksoftirqd[RCU_SOFTIRQ],
+ .setup = ksoftirqd_set_sched_params,
+ .cleanup = ksoftirqd_clr_sched_params,
+ .thread_should_run = ksoftirqd_should_run,
+ .thread_fn = run_ksoftirqd,
+ .thread_comm = "sirq-rcu/%u",
+ },
+#endif
};

static __init int spawn_ksoftirqd(void)
{
+ struct smp_hotplug_thread *t = &softirq_threads[threadsirqs];
+ int i, threads = NR_SOFTIRQ_THREADS;
+
register_cpu_notifier(&cpu_nfb);

- BUG_ON(smpboot_register_percpu_thread(&softirq_threads));
+ for (i = 0; i < threads; i++, t++) {
+ BUG_ON(smpboot_register_percpu_thread(t));
+ if (!threadsirqs)
+ break;
+ }

return 0;
}



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