Re: [PATCH 1/3] PM: hibernate: Print speed statistics of copy_data_pages()

[Rafael J. Wysocki]

On Mon, May 18, 2026 at 11:34 PM Nícolas F. R. A. Prado
<nfraprado@xxxxxxxxxxxxx> wrote:
>
> copy_data_pages() can take a long (multi-second) time to finish, and
> currently the only indication of that is the timestamp difference
> between print messages right before and right after. The timestamp is
> also immediately reset afterwards to the time before image creation,
> making it even harder to spot this delay. And this function runs in a
> critical section with a single CPU online and syscore suspended, so it
> should be kept as quick as possible to keep the system responsive.
>
> Call into swsusp_show_speed() to report the amount of data, time taken,
> and copy speed of copy_data_pages() to make it easier to spot delays and
> verify performance improvements. The current time is obtained through
> sched_clock() instead of ktime_get() since timekeeping is suspended in
> this region.

Why not use local_clock() for this?

> Signed-off-by: Nícolas F. R. A. Prado <nfraprado@xxxxxxxxxxxxx>
> ---
>  kernel/power/snapshot.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
> index e249e5786fbc..4f452baf31dc 100644
> --- a/kernel/power/snapshot.c
> +++ b/kernel/power/snapshot.c
> @@ -13,6 +13,7 @@
>  #include <linux/version.h>
>  #include <linux/module.h>
>  #include <linux/mm.h>
> +#include <linux/sched/clock.h>
>  #include <linux/suspend.h>
>  #include <linux/delay.h>
>  #include <linux/bitops.h>
> @@ -2109,6 +2110,7 @@ static int swsusp_alloc(struct memory_bitmap *copy_bm,
>  asmlinkage __visible int swsusp_save(void)
>  {
>         unsigned int nr_pages, nr_highmem;
> +       ktime_t start, stop;
>
>         pr_info("Creating image:\n");
>
> @@ -2132,7 +2134,10 @@ asmlinkage __visible int swsusp_save(void)
>          * Kill them.
>          */
>         drain_local_pages(NULL);
> +       start = ns_to_ktime(sched_clock());
>         nr_copy_pages = copy_data_pages(&copy_bm, &orig_bm, &zero_bm);
> +       stop = ns_to_ktime(sched_clock());
> +       swsusp_show_speed(start, stop, nr_copy_pages, "Copied");
>
>         /*
>          * End of critical section. From now on, we can write to memory,
>
> --
> 2.53.0
>