[linux-audio-dev] Re: mini Review: Re: [Jackit-devel] latest CVS commit

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Subject: [linux-audio-dev] Re: mini Review: Re: [Jackit-devel] latest CVS commit
From: Paul Davis (paul_AT_linuxaudiosystems.com)
Date: Tue Dec 02 2003 - 06:16:52 EET


>On Monday 01 December 2003 20.48, Paul Davis wrote:
>
>> i'd appreciate test reports ASAP, so that out trusty release
>> technician (the very wonderful taybin rutkin) can get a new release
>> out in the near future.
>>
>
>alsa_driver.c
>
> driver->period_usecs =3D
> (jack_time_t) floor ((((float) driver->frames_per_cycle) /
> driver->frame_rate) * 1000000.0f);
>
>jackd/engine.c
> poll_timeout =3D (engine->control->real_time =3D=3D 0 ?
> engine->client_timeout_msecs :
> engine->driver->period_usecs/1000);
>
> - - -
>
> if (poll (pfd, 1, poll_timeout) < 0) {
>
>Isn't this dangerous?
>* What happens if period_usecs < 1000?
> Well poll_timeout gets 0 since period_usecs is an uint64_t
> A poll with time out of zero will return immediately.
> OK?

well, there is no alternative really. the kernel has no time
resolution less than 1msec even on modern kernels with HZ=1000. so
setting it lower could be rather risky, given the use of busywaits for
some other SCHED_FIFO delays (see the code for usleep).

but yes, you are right, it is dangerous. we should probably sleep for
max (1msec, period_msecs). agree?


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