Re: [PATCH] delayacct: Preserve delay extrema when aggregating taskstats

[Bradley Morgan <brads@mainlining.org>]

On 21 October 2026 02:00:22 BST, Hungyu Lin <dennylin0707@gmail.com> wrote:
>delayacct_add_tsk() adds each task's statistics to the accumulated TGID
>statistics, but overwrites the delay maxima, minima and peak timestamps.
>Consequently, the last task determines these fields, and a task with no
>recorded delay can erase an earlier task's peak despite a nonzero total.
>
>Keep the largest maximum and its associated timestamp, and combine the
>minima with min_not_zero() since zero denotes an unrecorded delay. Apply
>this to CPU delay and the seven delay types handled by UPDATE_DELAY().
>Single-task queries still start with zeroed statistics and retain the
>task's values.

Hmm.


>
>Fixes: 658eb5ab916d ("delayacct: add delay max to record delay peak")
>Fixes: f65c64f311ee ("delayacct: add delay min to record delay peak")
>Cc: stable@vger.kernel.org
>Signed-off-by: Hungyu Lin <dennylin0707@gmail.com>
>---
> kernel/delayacct.c | 23 +++++++++++++++--------
> 1 file changed, 15 insertions(+), 8 deletions(-)
>
>diff --git a/kernel/delayacct.c b/kernel/delayacct.c
>index 479e860aff70..ea1424524654 100644
>--- a/kernel/delayacct.c
>+++ b/kernel/delayacct.c
>@@ -12,14 +12,18 @@
> #include <linux/taskstats.h>
> #include <linux/sysctl.h>
> #include <linux/delayacct.h>
>+#include <linux/minmax.h>
> #include <linux/module.h>
> 
> #define UPDATE_DELAY(type) \
> do { \
>-	d->type##_delay_max = tsk->delays->type##_delay_max; \
>-	d->type##_delay_min = tsk->delays->type##_delay_min; \
>-	d->type##_delay_max_ts.tv_sec = tsk->delays->type##_delay_max_ts.tv_sec; \
>-	d->type##_delay_max_ts.tv_nsec = tsk->delays->type##_delay_max_ts.tv_nsec; \
>+	if (tsk->delays->type##_delay_max > d->type##_delay_max) { \
>+		d->type##_delay_max = tsk->delays->type##_delay_max; \
>+		d->type##_delay_max_ts.tv_sec = tsk->delays->type##_delay_max_ts.tv_sec; \
>+		d->type##_delay_max_ts.tv_nsec = tsk->delays->type##_delay_max_ts.tv_nsec; \
>+	} \
>+	d->type##_delay_min = min_not_zero(d->type##_delay_min, \
>+					 tsk->delays->type##_delay_min); \
> 	tmp = d->type##_delay_total + tsk->delays->type##_delay; \
> 	d->type##_delay_total = (tmp < d->type##_delay_total) ? 0 : tmp; \
> 	d->type##_count += tsk->delays->type##_count; \
>@@ -174,10 +178,13 @@ int delayacct_add_tsk(struct taskstats *d, struct task_struct *tsk)
> 
> 	d->cpu_count += t1;
> 
>-	d->cpu_delay_max = tsk->sched_info.max_run_delay;
>-	d->cpu_delay_min = tsk->sched_info.min_run_delay;
>-	d->cpu_delay_max_ts.tv_sec = tsk->sched_info.max_run_delay_ts.tv_sec;
>-	d->cpu_delay_max_ts.tv_nsec = tsk->sched_info.max_run_delay_ts.tv_nsec;
>+	if (tsk->sched_info.max_run_delay > d->cpu_delay_max) {
>+		d->cpu_delay_max = tsk->sched_info.max_run_delay;
>+		d->cpu_delay_max_ts.tv_sec = tsk->sched_info.max_run_delay_ts.tv_sec;
>+		d->cpu_delay_max_ts.tv_nsec = tsk->sched_info.max_run_delay_ts.tv_nsec;
>+	}
>+	d->cpu_delay_min = min_not_zero(d->cpu_delay_min,
>+					tsk->sched_info.min_run_delay);
> 	tmp = (s64)d->cpu_delay_total + t2;

Makes sense, thanks

Reviewed-by: Bradley Morgan <brads@mainlining.org>

> 	d->cpu_delay_total = (tmp < (s64)d->cpu_delay_total) ? 0 : tmp;
> 	tmp = (s64)d->cpu_run_virtual_total + t3;
>


--- Thanks!
"I'm not a very positive person" - Linus torvalds