Messages in this thread | ![/](/images/icornerl.gif) | | Date | Thu, 23 Jun 2016 12:55:15 -0700 | From | Darren Hart <> | Subject | Re: futex: Allow FUTEX_CLOCK_REALTIME with FUTEX_WAIT op |
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On Thu, Jun 23, 2016 at 08:41:09PM +0200, Michael Kerrisk (man-pages) wrote: > On 06/23/2016 08:28 PM, Darren Hart wrote: > > On Thu, Jun 23, 2016 at 07:26:52PM +0200, Thomas Gleixner wrote: > > > On Thu, 23 Jun 2016, Darren Hart wrote: > > > > On Thu, Jun 23, 2016 at 03:40:36PM +0200, Thomas Gleixner wrote: > > > > In my opinion, we should treat the timeout value as relative for FUTEX_WAIT > > > > regardless of the CLOCK used. > > > > > > Which requires even more changes as you have to select which clock you are > > > using for adding the base time. > > > > Right, something like the following? > > > > > > diff --git a/kernel/futex.c b/kernel/futex.c > > index 33664f7..c39d807 100644 > > --- a/kernel/futex.c > > +++ b/kernel/futex.c > > @@ -3230,8 +3230,12 @@ SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val, > > return -EINVAL; > > > > t = timespec_to_ktime(ts); > > - if (cmd == FUTEX_WAIT) > > - t = ktime_add_safe(ktime_get(), t); > > + if (cmd == FUTEX_WAIT) { > > + if (cmd & FUTEX_CLOCK_REALTIME) > > + t = ktime_add_safe(ktime_get_real(), t); > > + else > > + t = ktime_add_safe(ktime_get(), t); > > + } > > tp = &t; > > } > > /* > > Just in the interests of readability/maintainability, might it not > make some sense to recode the timeout handling for FUTEX_WAIT > within futex_wait(). I think that part of the reason we're in this > mess of inconsistency is that timeout interpretation is being handled > at too many different points in the code.
I agree, that is indeed why I missed it in my original patch.
> > > And as a follow-on, what is the reason for FUTEX_LOCK_PI only using > > CLOCK_REALTIME? It seems reasonable to me that a user may want to wait a > > specific amount of time, regardless of wall time. > > Yes, that's another weird inconsistency. > > Thanks, > > Michael > > > -- > Michael Kerrisk > Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ > Linux/UNIX System Programming Training: http://man7.org/training/ >
-- Darren Hart Intel Open Source Technology Center
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