linux-kernel - Re: [PATCHv5 3/3] watchdog/softlockup: add SOFTLOCKUP_DETECTOR_INTR

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Date: Tue, 6 Feb 2024 13:42:12 -0800
From: Doug Anderson <dianders@...omium.org>
To: Bitao Hu <yaoma@...ux.alibaba.com>
Cc: akpm@...ux-foundation.org, pmladek@...e.com, kernelfans@...il.com, 
	liusong@...ux.alibaba.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv5 3/3] watchdog/softlockup: add SOFTLOCKUP_DETECTOR_INTR_STORM
 Kconfig knob

Hi,

On Tue, Feb 6, 2024 at 1:59 AM Bitao Hu <yaoma@...ux.alibaba.com> wrote:
>
> The interrupt storm detection mechanism we implemented requires a
> considerable amount of global storage space when configured for
> the maximum number of CPUs.
> Therefore, adding a SOFTLOCKUP_DETECTOR_INTR_STORM Kconfig knob that
> defaults to "yes" if the max number of CPUs is <= 128.
>
> Signed-off-by: Bitao Hu <yaoma@...ux.alibaba.com>
> ---
>  kernel/watchdog.c |  2 +-
>  lib/Kconfig.debug | 13 +++++++++++++
>  2 files changed, 14 insertions(+), 1 deletion(-)

IMO this should be squashed into patch #1, though I won't insist.


> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> index 26dc1ad86276..1595e4a94774 100644
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> @@ -338,7 +338,7 @@ __setup("watchdog_thresh=", watchdog_thresh_setup);
>
>  static void __lockup_detector_cleanup(void);
>
> -#ifdef CONFIG_IRQ_TIME_ACCOUNTING
> +#ifdef CONFIG_SOFTLOCKUP_DETECTOR_INTR_STORM
>  #define NUM_STATS_GROUPS       5
>  #define NUM_STATS_PER_GROUP    4
>  enum stats_per_group {
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 975a07f9f1cc..74002ba7c42d 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1029,6 +1029,19 @@ config SOFTLOCKUP_DETECTOR
>           chance to run.  The current stack trace is displayed upon
>           detection and the system will stay locked up.
>
> +config SOFTLOCKUP_DETECTOR_INTR_STORM
> +       bool "Detect Interrupt Storm in Soft Lockups"
> +       depends on SOFTLOCKUP_DETECTOR && IRQ_TIME_ACCOUNTING
> +       default y if NR_CPUS <= 128
> +       help
> +         Say Y here to enable the kernel to detect interrupt storm
> +         during "soft lockups".
> +
> +         "soft lockups" can be caused by a variety of reasons. If one is caused by
> +         an interrupt storm, then the storming interrupts will not be on the
> +         callstack. To detect this case, it is necessary to report the CPU stats
> +         and the interrupt counts during the "soft lockups".

It's probably not terribly important, but I notice that the other help
text in this file is generally wrapped to 80 columns. Even though the
kernel has relaxed the 80 column rule a bit, it still feels like this
could easily be wrapped to 80 columns without sacrificing any
readability.

In any case:

Reviewed-by: Douglas Anderson <dianders@...omium.org>