Messages in this thread | | | Date | Sat, 25 Oct 2014 19:32:09 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH v5] timekeeping: Added a function to return tv_sec portion of ktime_get_ts64() |
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On Sat, 25 Oct 2014, Arnd Bergmann wrote: > On Saturday 25 October 2014 17:22:23 Thomas Gleixner wrote: > > Hmm. Thinking more about it. That's actually overkill. For ktime_sec a > > 32bit value is plenty enough unless we care about systems with more > > than 136 years uptime. So if we calculate the seconds value of ktime, > > i.e. CLOCK_MONOTONIC, in the update function, we can read it on both > > 32 and 64bit w/o the seqcount loop. > > Ah, very good point. That opens the question which type that function > should return. I really want to remove all uses of time_t from the > kernel, mostly so we know when we're done with this. However as you > say we know that we only need a 32-bit value here. Some possible > ideas: > > - use time64_t here anyway and accept the slight inefficiency in return > for clarity
Probably the simplest option.
> - introduce a monotonic_time_t (we probably also want a struct > monotonic_timespec if we do that) which is basically the old time_t > but is known to be y2038 safe because we only ever use it to store > monotonic times.
Not sure whether its worth the trouble.
> - return u32 and use the same type in the callers instead of > time_t/time64_t/monotonic_time_t.
Works as well. I have no immediate preference.
> > Where we really need the above readout mechanism is get_seconds() as > > that will break in 2038 on 32bit. So there you need to change the > > return value from unsigned long to time64_t and change the > > implementation as above just xtime_sec instead of ktime_sec. > > Heena already posted a first draft of that patch to the opw internal > mailing list, I found a small issue that needs to be resolved and > then she can post the new version to you for review.
Great!
Thanks,
tglx
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