On Thu, 23 Jun 2016, Michael Kerrisk (man-pages) wrote: > On 06/23/2016 09:18 AM, Thomas Gleixner wrote: > Once upon a time, you told me the following: > > On 15 May 2014 at 16:14, Thomas Gleixner <t...@linutronix.de> wrote: > > On Thu, 15 May 2014, Michael Kerrisk (man-pages) wrote: > > > And that universe would love to have your documentation of > > > FUTEX_WAKE_BITSET and FUTEX_WAIT_BITSET ;-), > > > > I give you almost the full treatment, but I leave REQUEUE_PI to Darren > > and FUTEX_WAKE_OP to Jakub. :) > > [...] > > FUTEX_CLOCK_REALTIME > > > > This option bit can be ored on the futex ops FUTEX_WAIT_BITSET > > and FUTEX_WAIT_REQUEUE_PI > > > > If set the kernel treats the user space supplied timeout as > > absolute time based on CLOCK_REALTIME. > > > > If not set the kernel treats the user space supplied timeout > > as relative time. > Unfortunately, I should have checked the code more carefully...
Me too :) > Looking more carefully at the code, I see understand the situation > is the following: > > FUTEX_LOCK_PI > Always uses CLOCK_REALTIME > 'timeout' is absolute Yes. > FUTEX_WAIT_REQUEUE_PI > Choice of clock (CLOCK_REALTIME vs CLOCK_MONOTONIC) is > determined by presence or absence of > FUTEX_CLOCK_REALTIME flag > 'timeout' is absolute Yes > FUTEX_WAIT_BITSET > Choice of clock (CLOCK_REALTIME vs CLOCK_MONOTONIC) is > determined by presence or absence of > FUTEX_CLOCK_REALTIME flag > 'timeout' is absolute Yes > FUTEX_WAIT > Choice of clock (CLOCK_REALTIME vs CLOCK_MONOTONIC) is > determined by presence or absence of > FUTEX_CLOCK_REALTIME flag > 'timeout' is relative Yes. > I've amended the man page to describe those details. > > > The flag was explicitely added to allow FUTEX_WAIT to hand in absolute time. > > When you say that the "flag was added", which flag do you mean? Or, did you > mean: "applying Matthieu's patch will allow FUTEX_WAIT to hand in absolute > time". I didn't express myself clearly. When Darren added the support for CLOCK_REALTIME to FUTEX_WAIT I think he wanted to add absolute timeout support. Anything else does not make sense. Thanks, tglx