Messages in this thread | | | Date | Sat, 25 Oct 2014 17:22:23 +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, Thomas Gleixner wrote: > On Sat, 25 Oct 2014, Heena Sirwani wrote: > > +time64_t ktime_get_seconds(void) > > +{ > > + time64_t ts; > > + struct timekeeper *tk = &tk_core.timekeeper; > > + struct timespec64 tomono; > > + s32 nsec; > > + unsigned int seq; > > + > > + WARN_ON(timekeeping_suspended); > > + > > + do { > > + seq = read_seqcount_begin(&tk_core.seq); > > + ts = tk->xtime_sec; > > + nsec = (long)(tk->tkr.xtime_nsec >> tk->tkr.shift); > > + tomono = tk->wall_to_monotonic; > > + > > + } while (read_seqcount_retry(&tk_core.seq, seq)); > > + > > + ts += tomono.tv_sec; > > + if (nsec + tomono.tv_nsec >= NSEC_PER_SEC) > > + ts += 1; > > + return ts; > > I'd rather have an extra field in the timekeeper > > u64 xtime_sec; > + u64 ktime_sec; > > and update this in tk_update_ktime_data() so the readout function > boils down to > > time64_t ktime_get_seconds(void) > { > #if BITS_PER_LONG < 64 > u64 sec; > int seq; > > do { > seq = read_seqcount_begin(&tk_core.seq); > sec = tk->ktime_sec; > } while (read_seqcount_retry(&tk_core.seq, seq)); > > return sec; > #else > return tk->ktime_sec; > #endif > } > > So 64bit can do w/o the seqcount and 32bit avoids all extra math, right?
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.
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.
Thanks,
tglx
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