Hi Peter & Uladzislau
Are there any issues that have not been considered in this patch? Can
you give me some suggestions on this issue. If the situation I
described is indeed a problem，how about this modification. Thanks a
lot.
On Mon, Jul 20, 2020 at 9:09 PM <qianjun.ker...@gmail.com> wrote:
>
> From: jun qian <qianjun.ker...@gmail.com>
>
> 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 <qianjun.ker...@gmail.com>
> ---
> kernel/softirq.c | 20 +++++++++++++++++---
> 1 file changed, 17 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/softirq.c b/kernel/softirq.c
> index c4201b7f..f8e5be9 100644
> --- a/kernel/softirq.c
> +++ b/kernel/softirq.c
> @@ -210,7 +210,7 @@ void __local_bh_enable_ip(unsigned long ip, unsigned int
> cnt)
> * 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 2000 /* In microseconds */
> #define MAX_SOFTIRQ_RESTART 10
>
> #ifdef CONFIG_TRACE_IRQFLAGS
> @@ -248,7 +248,8 @@ static inline void lockdep_softirq_end(bool in_hardirq) {
> }
>
> asmlinkage __visible void __softirq_entry __do_softirq(void)
> {
> - unsigned long end = jiffies + MAX_SOFTIRQ_TIME;
> + ktime_t end, start;
> + s64 delta;
> unsigned long old_flags = current->flags;
> int max_restart = MAX_SOFTIRQ_RESTART;
> struct softirq_action *h;
> @@ -256,6 +257,8 @@ asmlinkage __visible void __softirq_entry
> __do_softirq(void)
> __u32 pending;
> int softirq_bit;
>
> + start = ktime_get();
> +
> /*
> * Mask out PF_MEMALLOC as the current task context is borrowed for
> the
> * softirq. A softirq handled, such as network RX, might set
> PF_MEMALLOC
> @@ -299,6 +302,15 @@ asmlinkage __visible void __softirq_entry
> __do_softirq(void)
> }
> h++;
> pending >>= softirq_bit;
> +
> + end = ktime_get();
> + delta = ktime_to_us(end - start);
> + /*
> + * the softirq's action has been running for too much time
> + * so it may need to wakeup the ksoftirqd
> + */
> + if (delta > MAX_SOFTIRQ_TIME && need_resched())
> + break;
> }
>
> if (__this_cpu_read(ksoftirqd) == current)
> @@ -307,7 +319,9 @@ asmlinkage __visible void __softirq_entry
> __do_softirq(void)
>
> pending = local_softirq_pending();
> if (pending) {
> - if (time_before(jiffies, end) && !need_resched() &&
> + end = ktime_get();
> + delta = ktime_to_us(end - start);
> + if (delta < MAX_SOFTIRQ_TIME && !need_resched() &&
> --max_restart)
> goto restart;
>
> --
> 1.8.3.1
>
