Messages in this thread Patch in this message | | | Date | Wed, 21 Sep 2022 01:25:50 +0000 | Subject | [RFC PATCH v3 3/3] softirq: defer softirq processing to ksoftirqd if CPU is busy with RT | From | John Stultz <> |
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From: Pavankumar Kondeti <pkondeti@codeaurora.org>
Defer the softirq processing to ksoftirqd if a RT task is running or queued on the current CPU. This complements the RT task placement algorithm which tries to find a CPU that is not currently busy with softirqs.
Currently NET_TX, NET_RX, BLOCK and TASKLET softirqs are only deferred as they can potentially run for long time.
Additionally, this patch stubs out ksoftirqd_running() logic, in the CONFIG_RT_SOFTIRQ_OPTIMIZATION case, as deferring potentially long-running softirqs will cause the logic to not process shorter-running softirqs immediately. By stubbing it out the potentially long running softirqs are deferred, but the shorter running ones can still run immediately.
This patch includes folded-in fixes by: Lingutla Chandrasekhar <clingutla@codeaurora.org> Satya Durga Srinivasu Prabhala <satyap@codeaurora.org> J. Avila <elavila@google.com>
Cc: John Dias <joaodias@google.com> Cc: Connor O'Brien <connoro@google.com> Cc: Rick Yiu <rickyiu@google.com> Cc: John Kacur <jkacur@redhat.com> Cc: Qais Yousef <qais.yousef@arm.com> Cc: Chris Redpath <chris.redpath@arm.com> Cc: Abhijeet Dharmapurikar <adharmap@quicinc.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Vincent Guittot <vincent.guittot@linaro.org> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: kernel-team@android.com Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org> [satyap@codeaurora.org: trivial merge conflict resolution.] Signed-off-by: Satya Durga Srinivasu Prabhala <satyap@codeaurora.org> [elavila: Port to mainline, squash with bugfix] Signed-off-by: J. Avila <elavila@google.com> [jstultz: Rebase to linus/HEAD, minor rearranging of code, included bug fix Reported-by: Qais Yousef <qais.yousef@arm.com> ] Signed-off-by: John Stultz <jstultz@google.com> --- include/linux/sched.h | 10 ++++++++++ kernel/sched/cpupri.c | 13 +++++++++++++ kernel/softirq.c | 25 +++++++++++++++++++++++-- 3 files changed, 46 insertions(+), 2 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h index e7b2f8a5c711..7f76371cbbb0 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1826,6 +1826,16 @@ current_restore_flags(unsigned long orig_flags, unsigned long flags) extern int cpuset_cpumask_can_shrink(const struct cpumask *cur, const struct cpumask *trial); extern int task_can_attach(struct task_struct *p, const struct cpumask *cs_effective_cpus); + +#ifdef CONFIG_RT_SOFTIRQ_OPTIMIZATION +extern bool cpupri_check_rt(void); +#else +static inline bool cpupri_check_rt(void) +{ + return false; +} +#endif + #ifdef CONFIG_SMP extern void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask); extern int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask); diff --git a/kernel/sched/cpupri.c b/kernel/sched/cpupri.c index fa9ce9d83683..18dc75d16951 100644 --- a/kernel/sched/cpupri.c +++ b/kernel/sched/cpupri.c @@ -64,6 +64,19 @@ static int convert_prio(int prio) return cpupri; } +#ifdef CONFIG_RT_SOFTIRQ_OPTIMIZATION +/* + * cpupri_check_rt - check if CPU has a RT task + * should be called from rcu-sched read section. + */ +bool cpupri_check_rt(void) +{ + int cpu = raw_smp_processor_id(); + + return cpu_rq(cpu)->rd->cpupri.cpu_to_pri[cpu] > CPUPRI_NORMAL; +} +#endif + static inline int __cpupri_find(struct cpupri *cp, struct task_struct *p, struct cpumask *lowest_mask, int idx) { diff --git a/kernel/softirq.c b/kernel/softirq.c index 35ee79dd8786..203a70dc9459 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -87,6 +87,7 @@ static void wakeup_softirqd(void) wake_up_process(tsk); } +#ifndef CONFIG_RT_SOFTIRQ_OPTIMIZATION /* * If ksoftirqd is scheduled, we do not want to process pending softirqs * right now. Let ksoftirqd handle this at its own rate, to get fairness, @@ -101,6 +102,9 @@ static bool ksoftirqd_running(unsigned long pending) return false; return tsk && task_is_running(tsk) && !__kthread_should_park(tsk); } +#else +#define ksoftirqd_running(pending) (false) +#endif /* CONFIG_RT_SOFTIRQ_OPTIMIZATION */ #ifdef CONFIG_TRACE_IRQFLAGS DEFINE_PER_CPU(int, hardirqs_enabled); @@ -532,6 +536,17 @@ static inline bool lockdep_softirq_start(void) { return false; } static inline void lockdep_softirq_end(bool in_hardirq) { } #endif +static __u32 softirq_deferred_for_rt(__u32 *pending) +{ + __u32 deferred = 0; + + if (cpupri_check_rt()) { + deferred = *pending & LONG_SOFTIRQ_MASK; + *pending &= ~LONG_SOFTIRQ_MASK; + } + return deferred; +} + asmlinkage __visible void __softirq_entry __do_softirq(void) { unsigned long end = jiffies + MAX_SOFTIRQ_TIME; @@ -539,6 +554,7 @@ asmlinkage __visible void __softirq_entry __do_softirq(void) int max_restart = MAX_SOFTIRQ_RESTART; struct softirq_action *h; bool in_hardirq; + __u32 deferred; __u32 pending; int softirq_bit; @@ -551,13 +567,15 @@ asmlinkage __visible void __softirq_entry __do_softirq(void) pending = local_softirq_pending(); + deferred = softirq_deferred_for_rt(&pending); softirq_handle_begin(); + in_hardirq = lockdep_softirq_start(); account_softirq_enter(current); restart: /* Reset the pending bitmask before enabling irqs */ - set_softirq_pending(0); + set_softirq_pending(deferred); __this_cpu_write(active_softirqs, pending); local_irq_enable(); @@ -596,13 +614,16 @@ asmlinkage __visible void __softirq_entry __do_softirq(void) local_irq_disable(); pending = local_softirq_pending(); + deferred = softirq_deferred_for_rt(&pending); + if (pending) { if (time_before(jiffies, end) && !need_resched() && --max_restart) goto restart; + } + if (pending | deferred) wakeup_softirqd(); - } account_softirq_exit(current); lockdep_softirq_end(in_hardirq); -- 2.37.3.968.ga6b4b080e4-goog
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