Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1539069

Re: [patch 5/6] [RFD] timekeeping: Provide optional 128bit math

Show all headers | View raw

On Fri, Dec 09, 2016 at 05:08:26AM +0100, Ingo Molnar wrote:
> > +#if defined(CONFIG_ARCH_SUPPORTS_INT128) && defined(__SIZEOF_INT128__)
> > +static inline u64 timekeeping_delta_to_ns(struct tk_read_base *tkr, u64 delta)
> > +{
> > +	unsigned __int128 nsec;
> > +
> > +	nsec = ((unsigned __int128)delta * tkr->mult) + tkr->xtime_nsec;
> > +	return (u64) (nsec >> tkr->shift);
> > +}
> 
> Actually, 128-bit multiplication shouldn't be too horrible - at least on 64-bit 
> architectures. (128-bit division is another matter, but there's no division here.)

IIRC there are 64bit architectures that do not have a 64x64->128 mult,
only a 64x64->64 mult instruction. Its not immediately apparent using
__int128 will generate optimal code for those, nor is it a given GCC
will not require libgcc functions for those.

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[patch 0/6] timekeeping: Cure the signed/unsigned wreckage Thomas Gleixner <tglx@linutronix.de> - 2016-12-08 22:00 +0100
  [patch 5/6] [RFD] timekeeping: Provide optional 128bit math Thomas Gleixner <tglx@linutronix.de> - 2016-12-08 22:00 +0100
    Re: [patch 5/6] [RFD] timekeeping: Provide optional 128bit math Ingo Molnar <mingo@kernel.org> - 2016-12-09 05:10 +0100
      Re: [patch 5/6] [RFD] timekeeping: Provide optional 128bit math Ingo Molnar <mingo@kernel.org> - 2016-12-09 05:30 +0100
        Re: [patch 5/6] [RFD] timekeeping: Provide optional 128bit math John Stultz <john.stultz@linaro.org> - 2016-12-09 05:50 +0100
      Re: [patch 5/6] [RFD] timekeeping: Provide optional 128bit math Peter Zijlstra <peterz@infradead.org> - 2016-12-09 05:50 +0100
        Re: [patch 5/6] [RFD] timekeeping: Provide optional 128bit math Ingo Molnar <mingo@kernel.org> - 2016-12-09 06:30 +0100
          Re: [patch 5/6] [RFD] timekeeping: Provide optional 128bit math Peter Zijlstra <peterz@infradead.org> - 2016-12-09 06:50 +0100
    Re: [patch 5/6] [RFD] timekeeping: Provide optional 128bit math Peter Zijlstra <peterz@infradead.org> - 2016-12-09 06:20 +0100
      Re: [patch 5/6] [RFD] timekeeping: Provide optional 128bit math Peter Zijlstra <peterz@infradead.org> - 2016-12-09 07:10 +0100
    Re: [patch 5/6] [RFD] timekeeping: Provide optional 128bit math Peter Zijlstra <peterz@infradead.org> - 2016-12-09 06:30 +0100
      Re: [patch 5/6] [RFD] timekeeping: Provide optional 128bit math Peter Zijlstra <peterz@infradead.org> - 2016-12-09 07:40 +0100
        Re: [patch 5/6] [RFD] timekeeping: Provide optional 128bit math Peter Zijlstra <peterz@infradead.org> - 2016-12-09 09:40 +0100
          Re: [patch 5/6] [RFD] timekeeping: Provide optional 128bit math Peter Zijlstra <peterz@infradead.org> - 2016-12-09 10:20 +0100
          Re: [patch 5/6] [RFD] timekeeping: Provide optional 128bit math Peter Zijlstra <peterz@infradead.org> - 2016-12-09 11:10 +0100
        Re: [patch 5/6] [RFD] timekeeping: Provide optional 128bit math Peter Zijlstra <peterz@infradead.org> - 2016-12-09 11:20 +0100
  [patch 3/6] timekeeping: Get rid of pointless typecasts Thomas Gleixner <tglx@linutronix.de> - 2016-12-08 22:00 +0100
    Re: [patch 3/6] timekeeping: Get rid of pointless typecasts David Gibson <david@gibson.dropbear.id.au> - 2016-12-09 00:50 +0100
    [tip:timers/core] timekeeping: Get rid of pointless typecasts tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2016-12-09 12:20 +0100
  Re: [patch 0/6] timekeeping: Cure the signed/unsigned wreckage John Stultz <john.stultz@linaro.org> - 2016-12-09 06:00 +0100
  Re: [patch 0/6] timekeeping: Cure the signed/unsigned wreckage Peter Zijlstra <peterz@infradead.org> - 2016-12-09 06:40 +0100

csiph-web