From: jun qian <[email protected]> When get the pending softirqs, it need to process all the pending softirqs in the while loop. If the processing time of each pending softirq is need more than 2 msec in this loop, or one of the softirq will running a long time, according to the original code logic, it will process all the pending softirqs without wakeuping ksoftirqd, which will cause a relatively large scheduling delay on the corresponding CPU, which we do not wish to see. The patch will check the total time to process pending softirq, if the time exceeds 2 ms we need to wakeup the ksofirqd to aviod large sched delay.
Signed-off-by: jun qian <[email protected]> --- kernel/softirq.c | 28 ++++++++++++++++++++-------- 1 file changed, 20 insertions(+), 8 deletions(-) diff --git a/kernel/softirq.c b/kernel/softirq.c index c4201b7f..d572ce4 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -25,6 +25,7 @@ #include <linux/smpboot.h> #include <linux/tick.h> #include <linux/irq.h> +#include <linux/sched/clock.h> #define CREATE_TRACE_POINTS #include <trace/events/irq.h> @@ -200,17 +201,15 @@ void __local_bh_enable_ip(unsigned long ip, unsigned int cnt) /* * We restart softirq processing for at most MAX_SOFTIRQ_RESTART times, * but break the loop if need_resched() is set or after 2 ms. - * The MAX_SOFTIRQ_TIME provides a nice upper bound in most cases, but in - * certain cases, such as stop_machine(), jiffies may cease to - * increment and so we need the MAX_SOFTIRQ_RESTART limit as - * well to make sure we eventually return from this method. + * In the loop, if the processing time of the softirq has exceeded 2 + * milliseconds, we also need to break the loop to wakeup the ksofirqd. * * These limits have been established via experimentation. * The two things to balance is latency against fairness - * we want to handle softirqs as soon as possible, but they * should not be able to lock up the box. */ -#define MAX_SOFTIRQ_TIME msecs_to_jiffies(2) +#define MAX_SOFTIRQ_TIME_NS 2000000 #define MAX_SOFTIRQ_RESTART 10 #ifdef CONFIG_TRACE_IRQFLAGS @@ -248,7 +247,7 @@ static inline void lockdep_softirq_end(bool in_hardirq) { } asmlinkage __visible void __softirq_entry __do_softirq(void) { - unsigned long end = jiffies + MAX_SOFTIRQ_TIME; + u64 end = sched_clock() + MAX_SOFTIRQ_TIME_NS; unsigned long old_flags = current->flags; int max_restart = MAX_SOFTIRQ_RESTART; struct softirq_action *h; @@ -299,6 +298,19 @@ asmlinkage __visible void __softirq_entry __do_softirq(void) } h++; pending >>= softirq_bit; + + /* + * the softirq's action has been running for too much time + * so it may need to wakeup the ksoftirqd + */ + if (need_resched() && sched_clock() > end) { + /* + * Ensure that the remaining pending bits are + * handled. + */ + or_softirq_pending(pending << (vec_nr + 1)); + break; + } } if (__this_cpu_read(ksoftirqd) == current) @@ -307,8 +319,8 @@ asmlinkage __visible void __softirq_entry __do_softirq(void) pending = local_softirq_pending(); if (pending) { - if (time_before(jiffies, end) && !need_resched() && - --max_restart) + if (!need_resched() && --max_restart && + sched_clock() <= end) goto restart; wakeup_softirqd(); -- 1.8.3.1
