user/sven/linux.git/include/linux/jiffies.h, branch v3.10.106

jiffies: Fix timeval conversion to jiffies

2014-10-09T19:18:43Z

commit d78c9300c51d6ceed9f6d078d4e9366f259de28c upstream. timeval_to_jiffies tried to round a timeval up to an integral number of jiffies, but the logic for doing so was incorrect: intervals corresponding to exactly N jiffies would become N+1. This manifested itself particularly repeatedly stopping/starting an itimer: setitimer(ITIMER_PROF, &val, NULL); setitimer(ITIMER_PROF, NULL, &val); would add a full tick to val, _even if it was exactly representable in terms of jiffies_ (say, the result of a previous rounding.) Doing this repeatedly would cause unbounded growth in val. So fix the math. Here's what was wrong with the conversion: we essentially computed (eliding seconds) jiffies = usec * (NSEC_PER_USEC/TICK_NSEC) by using scaling arithmetic, which took the best approximation of NSEC_PER_USEC/TICK_NSEC with denominator of 2^USEC_JIFFIE_SC = x/(2^USEC_JIFFIE_SC), and computed: jiffies = (usec * x) >> USEC_JIFFIE_SC and rounded this calculation up in the intermediate form (since we can't necessarily exactly represent TICK_NSEC in usec.) But the scaling arithmetic is a (very slight) *over*approximation of the true value; that is, instead of dividing by (1 usec/ 1 jiffie), we effectively divided by (1 usec/1 jiffie)-epsilon (rounding down). This would normally be fine, but we want to round timeouts up, and we did so by adding 2^USEC_JIFFIE_SC - 1 before the shift; this would be fine if our division was exact, but dividing this by the slightly smaller factor was equivalent to adding just _over_ 1 to the final result (instead of just _under_ 1, as desired.) In particular, with HZ=1000, we consistently computed that 10000 usec was 11 jiffies; the same was true for any exact multiple of TICK_NSEC. We could possibly still round in the intermediate form, adding something less than 2^USEC_JIFFIE_SC - 1, but easier still is to convert usec->nsec, round in nanoseconds, and then convert using time*spec*_to_jiffies. This adds one constant multiplication, and is not observably slower in microbenchmarks on recent x86 hardware. Tested: the following program: int main() { struct itimerval zero = {{0, 0}, {0, 0}}; /* Initially set to 10 ms. */ struct itimerval initial = zero; initial.it_interval.tv_usec = 10000; setitimer(ITIMER_PROF, &initial, NULL); /* Save and restore several times. */ for (size_t i = 0; i < 10; ++i) { struct itimerval prev; setitimer(ITIMER_PROF, &zero, &prev); /* on old kernels, this goes up by TICK_USEC every iteration */ printf("previous value: %ld %ld %ld %ld\n", prev.it_interval.tv_sec, prev.it_interval.tv_usec, prev.it_value.tv_sec, prev.it_value.tv_usec); setitimer(ITIMER_PROF, &prev, NULL); } return 0; } Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Paul Turner Cc: Richard Cochran Cc: Prarit Bhargava Reviewed-by: Paul Turner Reported-by: Aaron Jacobs Signed-off-by: Andrew Hunter [jstultz: Tweaked to apply to 3.17-rc] Signed-off-by: John Stultz [bwh: Backported to 3.16: adjust filename] Signed-off-by: Ben Hutchings Signed-off-by: Greg Kroah-Hartman

jiffies: Avoid undefined behavior from signed overflow

2014-03-24T04:38:20Z

commit 5a581b367b5df0531265311fc681c2abd377e5e6 upstream. According to the C standard 3.4.3p3, overflow of a signed integer results in undefined behavior. This commit therefore changes the definitions of time_after(), time_after_eq(), time_after64(), and time_after_eq64() to avoid this undefined behavior. The trick is that the subtraction is done using unsigned arithmetic, which according to 6.2.5p9 cannot overflow because it is defined as modulo arithmetic. This has the added (though admittedly quite small) benefit of shortening four lines of code by four characters each. Note that the C standard considers the cast from unsigned to signed to be implementation-defined, see 6.3.1.3p3. However, on a two's-complement system, an implementation that defines anything other than a reinterpretation of the bits is free to come to me, and I will be happy to act as a witness for its being committed to an insane asylum. (Although I have nothing against saturating arithmetic or signals in some cases, these things really should not be the default when compiling an operating-system kernel.) Signed-off-by: Paul E. McKenney Cc: John Stultz Cc: "David S. Miller" Cc: Arnd Bergmann Cc: Ingo Molnar Cc: Linus Torvalds Cc: Eric Dumazet Cc: Kevin Easton [ paulmck: Included time_after64() and time_after_eq64(), as suggested by Eric Dumazet, also fixed commit message.] Reviewed-by: Josh Triplett Ruchi Kandoi Signed-off-by: Greg Kroah-Hartman

timekeeping: Make jiffies_lock internal

2013-03-22T23:20:00Z

Nothing outside of the timekeeping core needs that lock. Signed-off-by: Thomas Gleixner Signed-off-by: John Stultz

time: Kill xtime_lock, replacing it with jiffies_lock

2012-11-13T19:08:23Z

Now that timekeeping is protected by its own locks, rename the xtime_lock to jifffies_lock to better describe what it protects. CC: Thomas Gleixner CC: Eric Dumazet CC: Richard Cochran Signed-off-by: John Stultz

Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2012-10-12T13:17:48Z

Pull timer core update from Thomas Gleixner: - Bug fixes (one for a longstanding dead loop issue) - Rework of time related vsyscalls - Alarm timer updates - Jiffies updates to remove compile time dependencies * 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: timekeeping: Cast raw_interval to u64 to avoid shift overflow timers: Fix endless looping between cascade() and internal_add_timer() time/jiffies: bring back unconditional LATCH definition time: Convert x86_64 to using new update_vsyscall time: Only do nanosecond rounding on GENERIC_TIME_VSYSCALL_OLD systems time: Introduce new GENERIC_TIME_VSYSCALL time: Convert CONFIG_GENERIC_TIME_VSYSCALL to CONFIG_GENERIC_TIME_VSYSCALL_OLD time: Move update_vsyscall definitions to timekeeper_internal.h time: Move timekeeper structure to timekeeper_internal.h for vsyscall changes jiffies: Remove compile time assumptions about CLOCK_TICK_RATE jiffies: Kill unused TICK_USEC_TO_NSEC alarmtimer: Rename alarmtimer_remove to alarmtimer_dequeue alarmtimer: Remove unused helpers & defines alarmtimer: Use hrtimer per-alarm instead of per-base alarmtimer: Implement minimum alarm interval for allowing suspend

Merge branch 'arnds-jiffies-fix' into fortglx/3.7/time

2012-09-28T22:00:27Z

Sort out conflict with Arnd's patch that preserves the unconditional LATCH value. Signed-off-by: John Stultz

time/jiffies: bring back unconditional LATCH definition

2012-09-28T21:58:22Z

Patch a7ea3bbf5d "time/jiffies: Allow CLOCK_TICK_RATE to be undefined" breaks the compilation of targets that rely on the LATCH definition, because of recursive header file inclusion not defining CLOCK_TICK_RATE before it is checked here. This fixes the problem by moving LATCH back to where it was, but it seems that there are still cases where SHIFTED_HZ is defined incorrectly because of the same problem. Need to investigate further. Without this patch, building h7201_defconfig results in: arch/arm/mach-h720x/common.c: In function 'h720x_gettimeoffset': arch/arm/mach-h720x/common.c:50:73: error: 'LATCH' undeclared (first use in this function) arch/arm/mach-h720x/common.c:50:73: note: each undeclared identifier is reported only once for each function it appears in arch/arm/mach-h720x/common.c:51:1: warning: control reaches end of non-void function [-Wreturn-type] Signed-off-by: Arnd Bergmann Cc: Catalin Marinas Cc: Richard Cochran Cc: Prarit Bhargava Cc: Andrew Morton Cc: John Stultz Cc: Ingo Molnar Signed-off-by: John Stultz

jiffies: Remove compile time assumptions about CLOCK_TICK_RATE

2012-09-24T16:38:05Z

CLOCK_TICK_RATE is used to accurately caclulate exactly how a tick will be at a given HZ. This is useful, because while we'd expect NSEC_PER_SEC/HZ, the underlying hardware will have some granularity limit, so we won't be able to have exactly HZ ticks per second. This slight error can cause timekeeping quality problems when using the jiffies or other jiffies driven clocksources. Thus we currently use compile time CLOCK_TICK_RATE value to generate SHIFTED_HZ and NSEC_PER_JIFFIES, which we then use to adjust the jiffies clocksource to correct this error. Unfortunately though, since CLOCK_TICK_RATE is a compile time value, and the jiffies clocksource is registered very early during boot, there are a number of cases where there are different possible hardware timers that have different tick rates. This causes problems in cases like ARM where there are numerous different types of hardware, each having their own compile-time CLOCK_TICK_RATE, making it hard to accurately support different hardware with a single kernel. For the most part, this doesn't matter all that much, as not too many systems actually utilize the jiffies or jiffies driven clocksource. Usually there are other highres clocksources who's granularity error is negligable. Even so, we have some complicated calcualtions that we do everywhere to handle these edge cases. This patch removes the compile time SHIFTED_HZ value, and introduces a register_refined_jiffies() function. This results in the default jiffies clock as being assumed a perfect HZ freq, and allows archtectures that care about jiffies accuracy to call register_refined_jiffies() with the tick rate, specified dynamically at boot. This allows us, where necessary, to not have a compile time CLOCK_TICK_RATE constant, simplifies the jiffies code, and still provides a way to have an accurate jiffies clock. NOTE: Since this patch does not add register_refinied_jiffies() calls for every arch, it may cause time quality regressions in some cases. Its likely these will not be noticable, but if they are an issue, adding the following to the end of setup_arch() should resolve the regression: register_refinied_jiffies(CLOCK_TICK_RATE) Cc: Catalin Marinas Cc: Arnd Bergmann Cc: Richard Cochran Cc: Prarit Bhargava Cc: Thomas Gleixner Signed-off-by: John Stultz

jiffies: Kill unused TICK_USEC_TO_NSEC

2012-09-24T16:38:04Z

No one is using TICK_USEC_TO_NSEC, so kill it. Cc: Catalin Marinas Cc: Arnd Bergmann Cc: Richard Cochran Cc: Prarit Bhargava Cc: Thomas Gleixner Signed-off-by: John Stultz

Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net

2012-08-22T21:21:38Z