On 2/28/25 15:16, Yao Zi wrote:
> On Fri, Feb 28, 2025 at 03:38:22PM +0200, Ilias Apalodimas wrote:
>> Hi Jerome,
>>
>> On Tue, 25 Feb 2025 at 18:35, Jerome Forissier
>> <jerome.foriss...@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.
I'll try to provide numbers in v3.
>>
>>>
>>> Signed-off-by: Jerome Forissier <jerome.foriss...@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?
>
> If I get the point, the UTHREAD is a cooperative framework, which means
> a task yields the control flow only when it considers nothing else could
> be done. And there's no preemption (at least in this revision). Thus I
> don't think it's a problem.
That's correct. Code always executes uninterrupted until it reaches
uthread_schedule().
Thanks,
--
Jerome
>
>> Thanks
>> /Ilias
>
> Best regards,
> Yao Zi
>
>>> + uthread_schedule();
>>> + } else {
>>> + __udelay(kv);
>>> + }
>>> usec -= kv;
>>> } while(usec);
>>> +
>>> }
>>> --
>>> 2.43.0
>>>
