From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751729AbaJYSso (ORCPT ); Sat, 25 Oct 2014 14:48:44 -0400 Received: from www.linutronix.de ([62.245.132.108]:50855 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751068AbaJYSsn (ORCPT ); Sat, 25 Oct 2014 14:48:43 -0400 Date: Sat, 25 Oct 2014 17:22:23 +0200 (CEST) From: Thomas Gleixner To: Heena Sirwani cc: linux-kernel@vger.kernel.org, john.stultz@linaro.org, arnd@arndb.de Subject: Re: [PATCH v5] timekeeping: Added a function to return tv_sec portion of ktime_get_ts64() In-Reply-To: Message-ID: References: <20141025123406.GA13128@heena.com> User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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