Messages in this thread | | | Date | Mon, 11 Jan 2016 09:15:25 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [PATCH RFC] timer: drop the unnecessary while loop in msleep |
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On Sat, 9 Jan 2016, Nicholas Mc Guire wrote:
> The while loop in msleep does not seem necessary as > timeout is unsigned long and no larger than MAX_JIFFY_OFFSET (which is > LONG_MAX/2 - 1) so the while-loop condition is always true at the beginning > (msecs_to_jiffies will return >=0 always and with the +1 timeout is >= 1 so > the while condition is always true at the start) and > schedule_timeout_uninterruptible always returns 0, so the while loop always > terminates after the first loop.
Err, no. schedule_timeout_uninterruptible() can return > 0 when there was a non timer wakeup. Thinks spurious wakeups. So we need that loop. > Q: what is the purpose of the + 1 offset to the jiffies here ? > > msleep was introduced in 2.6.7 but without the + 1, so with: > unsigned long timeout = msecs_to_jiffies(msecs); > in 2.6.10-rc2 the msecs_to_jiffies(msecs) + 1; is introduced. > Nishanth Aravamudan <nacc@us.ibm.com> (https://lkml.org/lkml/2004/11/19/294) > seems to be the origin while converting msleep to a macro, but no reason > for the + 1 is given there.
Not really. The +1 was introduced with the following commit:
https://git.kernel.org/cgit/linux/kernel/git/tglx/history.git/commit/kernel/timer.c?id=c259ef842622a5e64418d9dab3b62ee051867edf
Thanks,
tglx
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