Re: Can't sleep less than 20 ms

Rogier Wolff (R.E.Wolff@BitWizard.nl)
Sat, 3 Jul 1999 07:59:12 +0200 (MEST)

Dong Liu wrote:
> Boussard Per wrote:
> >
> > On Fri, 2 Jul 1999, Andrea Arcangeli wrote:
> >
> > >
> > > Set the policy of the scheduler as RT.
> > >
> >
> > This will only work for root, no? The problem is the tv_sec||tv_nsec
> > expression in sys_nanosleep(). I think this must go.
>
> This seems to be correct, I changed
>
> expire = timespec_to_jiffies(&t) + (t.tv_sec || t.tv_nsec);
> to
> expire = timespec_to_jiffies(&t);
>
> in sys_nanosleep(), now I got
>
> usleep ( <=10*1000) sleeps for 10 ms
> usleep ( >10*1000 <= 20*1000) sleeps for 20 ms
> usleep ( >20*1000 <= 30*1000) sleeps for 30 ms

This may be a nice hack for YOU, but in no way should this be in the
standard kernel.

This looks fine:

Clock interrupts + + + + +
App is waken up: * * * *
app calls usleep (9000) ^ ^ ^ ^

but... if the application uses 8ms of CPU time before calling
usleep again:

Clock interrupts + + + + +
App is waken up: * * * *
app calls usleep (9000) ^ ^ ^ ^

it will only sleep for 2ms before getting woken. And the manual states
that the sleep will be -=* at least *=- the number of microseconds
requested, and that you should always be prepared to be woken a little
later due to scheduling overhead or other tasks running.

Roger.

-- 
** R.E.Wolff@BitWizard.nl ** http://www.BitWizard.nl/ ** +31-15-2137555 **
*-- BitWizard writes Linux device drivers for any device you may have! --*
------ Microsoft SELLS you Windows, Linux GIVES you the whole house ------




-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.rutgers.edu
Please read the FAQ at http://www.tux.org/lkml/