On 3/4/25 16:24, Jerome Forissier 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. The granunlarity of the
> scheduling loop is defined by CONFIG_UTHREAD_GRANULARITY. The lower the
> value, the tighter the loop. The default value of 10 ms was chosen by
> testing the concurrent initialization of the two USB busses of an
> i.MX93 board (introduced in a later commit). The total time is as
> follows:
>
> UTHREAD_GRANULARITY (us) | "usb start" time (s)
> -------------------------+----------------------
> 0 | 2.426
> 1000 | 2.448
> 10000 | 2.512
> 100000 | 2.992
> 300000 | 3.407
>
> For reference, if uthread_schedule() is not called at all in udelay()
> except once via schedule(), the "usb start" time is 4.377s and without
> UTHREAD it is 4.591 s.
Replying to myself... but I have done some more tests on the i.MX93 and
this UTHREAD_GRANULARITY delay is not good. The console drops characters
as soon as it is greater than 5 microseconds. That's after running
"spawn sleep 10" -- the console becomes buggy during 10 seconds then back
to normal. With UTHREAD_GRANULARITY=0 all is fine.
Therefore I consider dropping UTHREAD_GRANULARITY in v4 and using a tight
loop like in v2 [1].
[1] https://lists.denx.de/pipermail/u-boot/2025-February/581634.html
--
Jerome
>
> Signed-off-by: Jerome Forissier <jerome.foriss...@linaro.org>
> ---
> lib/Kconfig | 8 ++++++++
> lib/time.c | 21 ++++++++++++++++++++-
> 2 files changed, 28 insertions(+), 1 deletion(-)
>
> diff --git a/lib/Kconfig b/lib/Kconfig
> index 8321f20e154..40964f5bb4a 100644
> --- a/lib/Kconfig
> +++ b/lib/Kconfig
> @@ -1276,6 +1276,14 @@ config UTHREAD_STACK_SIZE
> When the stack_sz argument to uthread_create() is zero then this
> value is used.
>
> +config UTHREAD_GRANULARITY
> + int "Scheduling period for uthreads inside udelay()"
> + depends on UTHREAD
> + default 10000
> + help
> + The delay in microseconds between calls to uthread_schedule() inside
> + the udelay() function.
> +
> endmenu
>
> source "lib/fwu_updates/Kconfig"
> diff --git a/lib/time.c b/lib/time.c
> index d88edafb196..7c34424bf64 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 */
> @@ -190,6 +191,23 @@ void __weak __udelay(unsigned long usec)
>
> /* -------------------------------------------------------------------------
> */
>
> +static void do_delay(unsigned long kv)
> +{
> +#if CONFIG_IS_ENABLED(UTHREAD)
> + ulong t0 = timer_get_us();
> + ulong gr = CONFIG_UTHREAD_GRANULARITY;
> +
> + if (kv < CONFIG_UTHREAD_GRANULARITY)
> + gr = kv;
> + while (timer_get_us() - t0 < kv) {
> + uthread_schedule();
> + __udelay(gr);
> + }
> +#else
> + __udelay(kv);
> +#endif
> +}
> +
> void udelay(unsigned long usec)
> {
> ulong kv;
> @@ -197,7 +215,8 @@ void udelay(unsigned long usec)
> do {
> schedule();
> kv = usec > CFG_WD_PERIOD ? CFG_WD_PERIOD : usec;
> - __udelay(kv);
> + do_delay(kv);
> usec -= kv;
> } while(usec);
> +
> }
