Re: [PATCH v2] delayacct: add timestamp of delay max

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 15 Jan 2026 23:52:37 +0800 (CST) <wang.yaxin@zte.com.cn> wrote:

> From: Wang Yaxin <wang.yaxin@zte.com.cn>
> Problem
> =======
> Commit 658eb5ab916d ("delayacct: add delay max to record delay peak")
> introduced the delay max for getdelays, which records abnormal latency
> peaks and helps us understand the magnitude of such delays. However,
> the peak latency value alone is insufficient for effective root cause
> analysis. Without the precise timestamp of when the peak occurred, we
> still lack the critical context needed to correlate it with other
> system events.
> 
> Solution
> ========
> To address this, we need to additionally record a precise timestamp
> when the maximum latency occurs. By correlating this timestamp with
> system logs and monitoring metrics, we can identify processes with
> abnormal resource usage at the same moment, which can help us to
> pinpoint root causes.

Seems sensible, thanks.

> Use Case
> ========
> bash-4.4# ./getdelays -d -t 227
> print delayacct stats ON
> TGID    227
> 
> 
> CPU         count     real total  virtual total    delay total  delay average      delay max      delay min      delay max timestamp
>                46      188000000      192348334        4098012          0.089ms     0.429260ms     0.051205ms    2026-01-15 15:06:58

"2026-01-15 15:06:58" isn't very friendly to parsers?  And because it
has a space it's two columns whereas everything else in here is a
single column.  Perhaps there's some more parser-friendly way of
presenting this?

>
> ...
>
> @@ -217,7 +223,8 @@ void __delayacct_freepages_end(void)
>  		      &current->delays->freepages_delay,
>  		      &current->delays->freepages_count,
>  		      &current->delays->freepages_delay_max,
> -		      &current->delays->freepages_delay_min);
> +		      &current->delays->freepages_delay_min,
> +			  &current->delays->freepages_delay_max_ts);
>  }

The whitespacing is inconsistent here.

>  void __delayacct_thrashing_start(bool *in_thrashing)
> @@ -241,7 +248,8 @@ void __delayacct_thrashing_end(bool *in_thrashing)
>  		      &current->delays->thrashing_delay,
>  		      &current->delays->thrashing_count,
>  		      &current->delays->thrashing_delay_max,
> -		      &current->delays->thrashing_delay_min);
> +		      &current->delays->thrashing_delay_min,
> +			  &current->delays->thrashing_delay_max_ts);
>  }

Many more instances of this.