linux-kernel - Re: [PATCH 2/9] softirq: Use sched

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Date:   Mon, 8 May 2023 12:08:04 +0800
From:   Jason Xing <kerneljasonxing@...il.com>
To:     Liu Jian <liujian56@...wei.com>
Cc:     corbet@....net, paulmck@...nel.org, frederic@...nel.org,
        quic_neeraju@...cinc.com, joel@...lfernandes.org,
        josh@...htriplett.org, boqun.feng@...il.com, rostedt@...dmis.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        qiang1.zhang@...el.com, jstultz@...gle.com, tglx@...utronix.de,
        sboyd@...nel.org, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com, peterz@...radead.org,
        frankwoo@...gle.com, Rhinewuwu@...gle.com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        rcu@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 2/9] softirq: Use sched_clock() based timeout

On Fri, May 5, 2023 at 7:25 PM Liu Jian <liujian56@...wei.com> wrote:
>
> From: Peter Zijlstra <peterz@...radead.org>
>
> Replace the jiffies based timeout with a sched_clock() based one.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Signed-off-by: Liu Jian <liujian56@...wei.com>
> ---
>  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
>
>