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Date: Mon, 27 Oct 2014 22:21:12 +0100 (CET) From: Thomas Gleixner <tglx@...utronix.de> To: Arnd Bergmann <arnd@...db.de> cc: Heena Sirwani <heenasirwani@...il.com>, linux-kernel@...r.kernel.org, john.stultz@...aro.org Subject: Re: [PATCH v5] timekeeping: Added a function to return tv_sec portion of ktime_get_ts64() On Sun, 26 Oct 2014, Arnd Bergmann wrote: > On Saturday 25 October 2014 17:12:48 Thomas Gleixner wrote: > > 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? > > > > But where would you set ktime_sec? My first thought was tk_update_ktime_data(), > but would then either be slightly wrong because it doesn't take the current > xtime_nsec + tk->wall_to_monotonic.tv_nsec into account, if we do > > diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c > index ec1791fae965..d72a456c6bd3 100644 > --- a/kernel/time/timekeeping.c > +++ b/kernel/time/timekeeping.c > @@ -426,8 +426,8 @@ static inline void tk_update_ktime_data(struct timekeeper *tk) > * nsec = base_mono + now(); > * ==> base_mono = (xtime_sec + wtm_sec) * 1e9 + wtm_nsec > */ > - nsec = (s64)(tk->xtime_sec + tk->wall_to_monotonic.tv_sec); > - nsec *= NSEC_PER_SEC; > + tk->ktime_sec = (s64)(tk->xtime_sec + tk->wall_to_monotonic.tv_sec); > + nsec = tk->ktime_sec * NSEC_PER_SEC; > nsec += tk->wall_to_monotonic.tv_nsec; > tk->tkr.base_mono = ns_to_ktime(nsec); > > > or we'd have to add an expensive timekeeping_get_ns() call: > > diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c > index ec1791fae965..d4c95b815de6 100644 > --- a/kernel/time/timekeeping.c > +++ b/kernel/time/timekeeping.c > @@ -426,9 +426,11 @@ static inline void tk_update_ktime_data(struct timekeeper *tk) > * nsec = base_mono + now(); > * ==> base_mono = (xtime_sec + wtm_sec) * 1e9 + wtm_nsec > */ > - nsec = (s64)(tk->xtime_sec + tk->wall_to_monotonic.tv_sec); > - nsec *= NSEC_PER_SEC; > - nsec += tk->wall_to_monotonic.tv_nsec; > + tk->ktime_sec = (s64)(tk->xtime_sec + tk->wall_to_monotonic.tv_sec); > + nsec = tk->wall_to_monotonic.tv_nsec; > + if ((nsec + timekeeping_get_ns()) > NSEC_PER_SEC) > + tk->ktime_sec += 1; > + nsec += tk->ktime_sec * NSEC_PER_SEC; > tk->tkr.base_mono = ns_to_ktime(nsec); No. Why would you do that? Look at the math you implemented and just do the same thing in the update function. Thanks, tglx -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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