Re: [PATCH 2/9] softirq: Use sched_clock() based timeout

[Jason Xing]

On Fri, May 5, 2023 at 7:25 PM Liu Jian <liujian56@xxxxxxxxxx> wrote:
>
> From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
>
> Replace the jiffies based timeout with a sched_clock() based one.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> Signed-off-by: Liu Jian <liujian56@xxxxxxxxxx>
> ---
>  kernel/softirq.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/softirq.c b/kernel/softirq.c
> index bff5debf6ce6..59f16a9af5d1 100644
> --- a/kernel/softirq.c
> +++ b/kernel/softirq.c
> @@ -27,6 +27,7 @@
>  #include <linux/tick.h>
>  #include <linux/irq.h>
>  #include <linux/wait_bit.h>
> +#include <linux/sched/clock.h>
>
>  #include <asm/softirq_stack.h>
>
> @@ -489,7 +490,7 @@ asmlinkage __visible void do_softirq(void)
>   * 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       (2 * NSEC_PER_MSEC)

I wonder if it affects those servers that set HZ to some different
values rather than 1000 as default.

Thanks,
Jason

>  #define MAX_SOFTIRQ_RESTART 10
>
>  #ifdef CONFIG_TRACE_IRQFLAGS
> @@ -527,9 +528,9 @@ static inline void lockdep_softirq_end(bool in_hardirq) { }
>
>  asmlinkage __visible void __softirq_entry __do_softirq(void)
>  {
> -       unsigned long end = jiffies + MAX_SOFTIRQ_TIME;
>         unsigned long old_flags = current->flags;
>         int max_restart = MAX_SOFTIRQ_RESTART;
> +       u64 start = sched_clock();
>         struct softirq_action *h;
>         unsigned long pending;
>         unsigned int vec_nr;
> @@ -584,7 +585,7 @@ asmlinkage __visible void __softirq_entry __do_softirq(void)
>
>         pending = local_softirq_pending();
>         if (pending) {
> -               if (time_before(jiffies, end) && !need_resched() &&
> +               if (sched_clock() - start < MAX_SOFTIRQ_TIME && !need_resched() &&
>                     --max_restart)
>                         goto restart;
>
> --
> 2.34.1
>
>