user/sven/linux.git/include/linux/jiffies.h, branch v3.2.83

jiffies: Fix timeval conversion to jiffies

2014-11-05T20:27:43Z

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 3.2: adjust filename] Signed-off-by: Ben Hutchings

jiffies: Avoid undefined behavior from signed overflow

2014-04-01T23:59:01Z

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 Signed-off-by: Ben Hutchings

time: Change jiffies_to_clock_t() argument type to unsigned long

2011-09-21T08:28:51Z

The parameter's origin type is long. On an i386 architecture, it can easily be larger than 0x80000000, causing this function to convert it to a sign-extended u64 type. Change the type to unsigned long so we get the correct result. Signed-off-by: hank Cc: John Stultz Cc: [ build fix ] Signed-off-by: Andrew Morton Signed-off-by: Thomas Gleixner Signed-off-by: Ingo Molnar

Fix common misspellings

2011-03-31T14:26:23Z

Fixes generated by 'codespell' and manually reviewed. Signed-off-by: Lucas De Marchi

time: Add nsecs_to_cputime64 interface for asm-generic

2011-01-26T11:33:20Z

Add nsecs_to_cputime64 interface. This is used in following patches that updates cpu irq stat based on ns granularity info in IRQ_TIME_ACCOUNTING. Tested-by: Shaun Ruffell Signed-off-by: Venkatesh Pallipadi Signed-off-by: Peter Zijlstra LKML-Reference: <1292980144-28796-3-git-send-email-venki@google.com> Signed-off-by: Ingo Molnar

sched, time: Define nsecs_to_jiffies()

2009-11-26T11:59:20Z

Use of msecs_to_jiffies() for nsecs_to_cputime() have some problems: - The type of msecs_to_jiffies()'s argument is unsigned int, so it cannot convert msecs greater than UINT_MAX = about 49.7 days. - msecs_to_jiffies() returns MAX_JIFFY_OFFSET if MSB of argument is set, assuming that input was negative value. So it cannot convert msecs greater than INT_MAX = about 24.8 days too. This patch defines a new function nsecs_to_jiffies() that can deal greater values, and that can deal all incoming values as unsigned. Signed-off-by: Hidetoshi Seto Acked-by: Peter Zijlstra Cc: Stanislaw Gruszka Cc: Spencer Candland Cc: Oleg Nesterov Cc: Balbir Singh Cc: Amrico Wang Cc: Thomas Gleixner Cc: John Stultz LKML-Reference: <4B0E16E7.5070307@jp.fujitsu.com> Signed-off-by: Ingo Molnar

optimize attribute timeouts for "noac" and "actimeo=0"

2008-12-23T20:21:56Z

Hi. I've been looking at a bugzilla which describes a problem where a customer was advised to use either the "noac" or "actimeo=0" mount options to solve a consistency problem that they were seeing in the file attributes. It turned out that this solution did not work reliably for them because sometimes, the local attribute cache was believed to be valid and not timed out. (With an attribute cache timeout of 0, the cache should always appear to be timed out.) In looking at this situation, it appears to me that the problem is that the attribute cache timeout code has an off-by-one error in it. It is assuming that the cache is valid in the region, [read_cache_jiffies, read_cache_jiffies + attrtimeo]. The cache should be considered valid only in the region, [read_cache_jiffies, read_cache_jiffies + attrtimeo). With this change, the options, "noac" and "actimeo=0", work as originally expected. This problem was previously addressed by special casing the attrtimeo == 0 case. However, since the problem is only an off- by-one error, the cleaner solution is address the off-by-one error and thus, not require the special case. Thanx... ps Signed-off-by: Peter Staubach Signed-off-by: Trond Myklebust

remove div_long_long_rem

2008-05-01T15:03:58Z

x86 is the only arch right now, which provides an optimized for div_long_long_rem and it has the downside that one has to be very careful that the divide doesn't overflow. The API is a little akward, as the arguments for the unsigned divide are signed. The signed version also doesn't handle a negative divisor and produces worse code on 64bit archs. There is little incentive to keep this API alive, so this converts the few users to the new API. Signed-off-by: Roman Zippel Cc: Ralf Baechle Cc: Ingo Molnar Cc: Thomas Gleixner Cc: john stultz Cc: Christoph Lameter Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/juhl/trivial

2008-04-21T23:36:46Z

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/juhl/trivial: (24 commits) DOC: A couple corrections and clarifications in USB doc. Generate a slightly more informative error msg for bad HZ fix typo "is" -> "if" in Makefile ext*: spelling fix prefered -> preferred DOCUMENTATION: Use newer DEFINE_SPINLOCK macro in docs. KEYS: Fix the comment to match the file name in rxrpc-type.h. RAID: remove trailing space from printk line DMA engine: typo fixes Remove unused MAX_NODES_SHIFT MAINTAINERS: Clarify access to OCFS2 development mailing list. V4L: Storage class should be before const qualifier (sn9c102) V4L: Storage class should be before const qualifier sonypi: Storage class should be before const qualifier intel_menlow: Storage class should be before const qualifier DVB: Storage class should be before const qualifier arm: Storage class should be before const qualifier ALSA: Storage class should be before const qualifier acpi: Storage class should be before const qualifier firmware_sample_driver.c: fix coding style MAINTAINERS: Add ati_remote2 driver ... Fixed up trivial conflicts in firmware_sample_driver.c

Generate a slightly more informative error msg for bad HZ

2008-04-21T22:56:14Z

Generate a slightly more informative error msg for bad HZ in include/linux/jiffies.h Signed-off-by: Robert P. J. Day Signed-off-by: Jesper Juhl