Re: [PATCH] pmac_cpufreq msleep cleanup/fixes

Nishanth Aravamudan
2004-10-22T23:46:50Z

On Sat, Oct 23, 2004 at 09:17:33AM +1000, Benjamin Herrenschmidt wrote:
> On Sat, 2004-10-23 at 08:53, Linus Torvalds wrote:
> > On Sat, 23 Oct 2004, Benjamin Herrenschmidt wrote:
> > >
> > > Please revert that change until we have made absolutely sure that msleep(1)
> > > on a HZ=1000 machine will actually sleep at least 1ms, this is really not
> > > clear since it will end up doing schedule_timeout(1) which, afaik, will
> > > only guarantee to sleep up to the next jiffie, which can be a lot shorter
> > > than the actual duration of a jiffie.
> >
> > In that case I'd much prefer to revert the whole previous "cleanup" as
> > well, since it obviously isn't really. Having
> >
> > msleep(1 + jiffy_to_ms(1));
> >
> > is just not a cleanup to me.
>
> This wasn't a cleanup but a bug fix actually ... Oh well, I think we need
> to fix msleep() instead, what do you think ? If we keep Nishanth's latest
> cleanup and fix msleep to add +1 to the delay, that would work and potentially
> fix other users as well ... provided my theory is right in the first place
> and that schedule_timeout(1) will indeed only sleep until the next jiffy and
> not for at least one jiffy...
>
> What about something like this ?
>

Looks good to me... And makes quite a bit of sense, after I thought
about it. Does feel a little hacky, but I don't see a slicker way around
the problem...

Makes sure msleep() sleeps at least the amount provided, since
schedule_timeout() doesn't guarantee a full jiffy.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Nishanth Aravamudan <nacc@us.ibm.com>

===== kernel/timer.c 1.100 vs edited =====
--- 1.100/kernel/timer.c 2004-10-19 19:40:28 +10:00
+++ edited/kernel/timer.c 2004-10-23 09:16:10 +10:00
@@ -1605,7 +1605,7 @@
*/
void msleep(unsigned int msecs)
{
- unsigned long timeout = msecs_to_jiffies(msecs);
+ unsigned long timeout = msecs_to_jiffies(msecs) + 1;

while (timeout) {
set_current_state(TASK_UNINTERRUPTIBLE);
@@ -1621,7 +1621,7 @@
*/
unsigned long msleep_interruptible(unsigned int msecs)
{
- unsigned long timeout = msecs_to_jiffies(msecs);
+ unsigned long timeout = msecs_to_jiffies(msecs) + 1;

while (timeout && !signal_pending(current)) {
set_current_state(TASK_INTERRUPTIBLE);