Messages in this thread | | | From | Linus Torvalds <> | Date | Mon, 25 Apr 2011 10:34:30 -0700 | Subject | Re: [PATCH 1/3] signal: sys_rt_sigtimedwait: simplify the timeout logic |
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On Mon, Apr 25, 2011 at 10:26 AM, Oleg Nesterov <oleg@redhat.com> wrote: > > If only I knew what this comment could say except > > /* Why do we add (tv_sec || tv_nsec) ? */ > > I'd better send 4/3 which simply removes this (I hope) unneeded code.
It's to guarantee that timeout is at least one tick more than asked for, because the rule is that you really have to wait for AT LEAST the time asked for. With the "zero timeout" being special, since that is "immediate".
Imagine that you ask for one timer tick - but that you're in the _middle_ of the current one. Waiting for the next timer is going to be too short - you'll only get half a timer tick. So we need to ask for "ceiling(nanoseconds / nanosecondspertick) + 1" to make sure that we really wait _longer_ than asked for.
So "+ (tv_sec || tv_nsec)" is just the "+1" for the "not zero timeout" case.
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