[PATCH v2 08/14] lib: time: hook uthread_schedule() into udelay()

[Ilias Apalodimas]

Hi Jerome,

On Tue, 25 Feb 2025 at 18:35, Jerome Forissier
<jerome.forissier at linaro.org> wrote:
>
> Introduce a uthread scheduling loop into udelay() when CONFIG_UTHREAD
> is enabled. This means that any uthread calling into udelay() may yield
> to uthread and be scheduled again later.
>
> While not strictly necessary since uthread_schedule() is already called
> by schedule(),
> tests show that it is desirable to call it in a tight
> loop instead of calling __usleep(). It gives more opportunities for
> other threads to make progress and results in better performances.

Some examples of timing gains would be nice.

>
> Signed-off-by: Jerome Forissier <jerome.forissier at linaro.org>
> ---
>  lib/time.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/lib/time.c b/lib/time.c
> index d88edafb196..d1a1a66f301 100644
> --- a/lib/time.c
> +++ b/lib/time.c
> @@ -17,6 +17,7 @@
>  #include <asm/global_data.h>
>  #include <asm/io.h>
>  #include <linux/delay.h>
> +#include <uthread.h>
>
>  #ifndef CFG_WD_PERIOD
>  # define CFG_WD_PERIOD (10 * 1000 * 1000)      /* 10 seconds default */
> @@ -197,7 +198,14 @@ void udelay(unsigned long usec)
>         do {
>                 schedule();
>                 kv = usec > CFG_WD_PERIOD ? CFG_WD_PERIOD : usec;
> -               __udelay(kv);
> +               if (CONFIG_IS_ENABLED(UTHREAD)) {
> +                       ulong t0 = timer_get_us();
> +                       while (timer_get_us() < t0 + kv)

Do we make progress by constantly scheduling new tasks? Perhaps we
should at least leave the task running for some time?

Thanks
/Ilias

> +                               uthread_schedule();
> +               } else {
> +                       __udelay(kv);
> +               }
>                 usec -= kv;
>         } while(usec);
> +
>  }
> --
> 2.43.0
>