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

[Zihuan Zhang]

Hi Rafael,
Thanks for the feedback.

在 2025/7/3 22:38, Rafael J. Wysocki 写道:
> On Thu, Jun 19, 2025 at 5:54 AM Zihuan Zhang <zhangzihuan@xxxxxxxxxx> 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@xxxxxxxxxx>
> > ---
> >   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?
I agree with your suggestion — I’ll switch to pr_debug() in the next 
version so that the message can 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
Best regards,
Zihuan Zhang