Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756700AbaDHXyg (ORCPT ); Tue, 8 Apr 2014 19:54:36 -0400 Received: from mga09.intel.com ([134.134.136.24]:63930 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756179AbaDHXyf (ORCPT ); Tue, 8 Apr 2014 19:54:35 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.97,820,1389772800"; d="scan'208";a="517110455" From: Tony Luck Date: Tue, 8 Apr 2014 10:32:23 -0700 Subject: [PATCH] time: Provide full featured jiffies_to_nsecs() function To: linux-kernel@vger.kernel.org Cc: Steven Rostedt , Frederic Weisbecker , Ingo Molnar , Mauro Chehab In-Reply-To: <20140408153412.0648fb96@gandalf.local.home> Message-Id: <0286550@agluck-desk.sc.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The "uptime" tracer added in: commit 8aacf017b065a805d27467843490c976835eb4a5 tracing: Add "uptime" trace clock that uses jiffies has wraparound problems when the system has been up more than 1 hour 11 minutes and 34 seconds. It converts jiffies to nanoseconds using: (u64)jiffies_to_usecs(jiffy) * 1000ULL but since jiffies_to_usecs() only returns a 32-bit value, it truncates at 2^32 microseconds. An additional problem on 32-bit systems is that the argument is "unsigned long", so fixing the return value only helps until 2^32 jiffies (49.7 days on a HZ=1000 system). So we provide a full featured jiffies_to_nsec() function that takes a "u64" argument and provides a "u64" result. To avoid cries of rage from the other user of this: scheduler_tick_max_deferment() we check whether the argument is small enough that we can do the calculations in 32-bit operations. Signed-off-by: Tony Luck --- include/linux/jiffies.h | 6 +----- kernel/time.c | 24 ++++++++++++++++++++++++ kernel/timeconst.bc | 12 ++++++++++++ kernel/trace/trace_clock.c | 2 +- 4 files changed, 38 insertions(+), 6 deletions(-) diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h index 1f44466c1e9d..3cf44401055f 100644 --- a/include/linux/jiffies.h +++ b/include/linux/jiffies.h @@ -294,11 +294,7 @@ extern unsigned long preset_lpj; */ extern unsigned int jiffies_to_msecs(const unsigned long j); extern unsigned int jiffies_to_usecs(const unsigned long j); - -static inline u64 jiffies_to_nsecs(const unsigned long j) -{ - return (u64)jiffies_to_usecs(j) * NSEC_PER_USEC; -} +extern u64 jiffies_to_nsecs(const u64 j); extern unsigned long msecs_to_jiffies(const unsigned int m); extern unsigned long usecs_to_jiffies(const unsigned int u); diff --git a/kernel/time.c b/kernel/time.c index 7c7964c33ae7..bbd18b0e5698 100644 --- a/kernel/time.c +++ b/kernel/time.c @@ -273,6 +273,30 @@ unsigned int jiffies_to_usecs(const unsigned long j) } EXPORT_SYMBOL(jiffies_to_usecs); +u64 jiffies_to_nsecs(const u64 jl) +{ + /* can we do this with 32-bit math? */ + if (jl < 4*HZ) { + unsigned long j = jl; +#if !(NSEC_PER_SEC % HZ) + return (NSEC_PER_SEC / HZ) * j; +#else +# if BITS_PER_LONG == 32 + return (HZ_TO_NSEC_MUL32 * j) >> HZ_TO_NSEC_SHR32; +# else + return (j * HZ_TO_NSEC_NUM) / HZ_TO_NSEC_DEN; +# endif +#endif + } else { +#if !(NSEC_PER_SEC % HZ) + return (NSEC_PER_SEC / HZ) * jl; +#else + return (jl * HZ_TO_NSEC_NUM) / HZ_TO_NSEC_DEN; +#endif + } +} +EXPORT_SYMBOL(jiffies_to_nsecs); + /** * timespec_trunc - Truncate timespec to a granularity * @t: Timespec diff --git a/kernel/timeconst.bc b/kernel/timeconst.bc index 511bdf2cafda..6f6e8b285c2b 100644 --- a/kernel/timeconst.bc +++ b/kernel/timeconst.bc @@ -100,6 +100,18 @@ define timeconst(hz) { print "#define USEC_TO_HZ_DEN\t\t", 1000000/cd, "\n" print "\n" + s=fmuls(32,1000000000,hz) + obase=16 + print "#define HZ_TO_NSEC_MUL32\tU64_C(0x", fmul(s,1000000000,hz), ")\n" + obase=10 + print "#define HZ_TO_NSEC_SHR32\t", s, "\n" + + obase=10 + cd=gcd(hz,1000000000) + print "#define HZ_TO_NSEC_NUM\t\t", 1000000000/cd, "\n" + print "#define HZ_TO_NSEC_DEN\t\t", hz/cd, "\n" + print "\n" + print "#endif /* KERNEL_TIMECONST_H */\n" } halt diff --git a/kernel/trace/trace_clock.c b/kernel/trace/trace_clock.c index 26dc348332b7..52470fba1d26 100644 --- a/kernel/trace/trace_clock.c +++ b/kernel/trace/trace_clock.c @@ -65,7 +65,7 @@ u64 notrace trace_clock_jiffies(void) u64 jiffy = jiffies - INITIAL_JIFFIES; /* Return nsecs */ - return (u64)jiffies_to_usecs(jiffy) * 1000ULL; + return jiffies_to_nsecs(jiffy); } /* -- 1.8.4.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/