linux-kernel - Re: [PATCH v2 1/4] PM: freezer: Add retry count statistics for freeze pass iterations

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Message-ID: <CAJZ5v0gLVTe0a8mTRhiDa_4NuFsYw8gPZF9dnLrZzFh3yt424Q@mail.gmail.com>
Date: Thu, 3 Jul 2025 16:38:41 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Zihuan Zhang <zhangzihuan@...inos.cn>
Cc: rafael@...nel.org, pavel@...nel.org, len.brown@...el.com, 
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/4] PM: freezer: Add retry count statistics for freeze
 pass iterations

On Thu, Jun 19, 2025 at 5:54 AM Zihuan Zhang <zhangzihuan@...inos.cn> wrote:
>
> Freezer retry loops during suspend are often triggered by tasks entering
> D-state (TASK_UNINTERRUPTIBLE), which cannot be frozen.  This patch adds
> a simple retry counter to freeze_processes() to help quantify how many
> attempts were required before all tasks entered the frozen state. This
> is useful for performance tuning and debugging unpredictable suspend
> delays.
>
> A new dmesg log is added for visibility:
>
> freeze round: xx, tasks to freeze: xx
>
> This message allows users to correlate freeze instability with system
> state.
>
> Signed-off-by: Zihuan Zhang <zhangzihuan@...inos.cn>
> ---
>  kernel/power/process.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/kernel/power/process.c b/kernel/power/process.c
> index dc0dfc349f22..87616ca710ac 100644
> --- a/kernel/power/process.c
> +++ b/kernel/power/process.c
> @@ -32,6 +32,7 @@ static int try_to_freeze_tasks(bool user_only)
>         struct task_struct *g, *p;
>         unsigned long end_time;
>         unsigned int todo;
> +       unsigned int retry = 0;
>         bool wq_busy = false;
>         ktime_t start, end, elapsed;
>         unsigned int elapsed_msecs;
> @@ -63,6 +64,8 @@ static int try_to_freeze_tasks(bool user_only)
>                         todo += wq_busy;
>                 }
>
> +               pm_pr_dbg("freeze round: %d, task to freeze: %d\n", retry, todo);
> +

This is kind of fine if it is really needed, but it needs to have a
separate on/off switch as far as I'm concerned.

Maybe use pr_debug() for it in which case it would be controlled via
dynamic debug?

>                 if (!todo || time_after(jiffies, end_time))
>                         break;
>
> @@ -79,6 +82,7 @@ static int try_to_freeze_tasks(bool user_only)
>                 usleep_range(sleep_usecs / 2, sleep_usecs);
>                 if (sleep_usecs < 8 * USEC_PER_MSEC)
>                         sleep_usecs *= 2;
> +               retry++;
>         }
>
>         end = ktime_get_boottime();
> --
> 2.25.1
>