* Re: [PATCH] make jiffies wrap 5 min after boot [not found] ` <20030216020808.GF9833@krispykreme.suse.lists.linux.kernel> @ 2003-02-16 6:36 ` Andi Kleen 2003-02-16 6:56 ` Andrew Morton 0 siblings, 1 reply; 12+ messages in thread From: Andi Kleen @ 2003-02-16 6:36 UTC (permalink / raw) To: Anton Blanchard; +Cc: linux-kernel, tim Anton Blanchard <anton@samba.org> writes: > Hi, > > > +#define INITIAL_JIFFIES (0xffffffffUL & (unsigned long)(-300*HZ)) > > In order to make 64bit arches wrap too, you might want to use -1UL here. > Not that jiffies should wrap on a 64bit machine... Seems somewhat pointless. (2^64-1) / (1000 * 3600 * 24 * 365) ~584942417.35507203243911719939 I doubt any system ever will have an uptime of > 584 million years (assuming HZ=1000) and if jiffies wrap will be the least of their problems. -Andi ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] make jiffies wrap 5 min after boot 2003-02-16 6:36 ` [PATCH] make jiffies wrap 5 min after boot Andi Kleen @ 2003-02-16 6:56 ` Andrew Morton 2003-02-16 7:00 ` Andi Kleen 2003-02-16 8:10 ` Tim Schmielau 0 siblings, 2 replies; 12+ messages in thread From: Andrew Morton @ 2003-02-16 6:56 UTC (permalink / raw) To: Andi Kleen; +Cc: anton, linux-kernel, tim Andi Kleen <ak@suse.de> wrote: > > Anton Blanchard <anton@samba.org> writes: > > > Hi, > > > > > +#define INITIAL_JIFFIES (0xffffffffUL & (unsigned long)(-300*HZ)) > > > > In order to make 64bit arches wrap too, you might want to use -1UL here. > > Not that jiffies should wrap on a 64bit machine... > > Seems somewhat pointless. > > (2^64-1) / (1000 * 3600 * 24 * 365) > ~584942417.35507203243911719939 > > I doubt any system ever will have an uptime of > 584 million years > (assuming HZ=1000) and if jiffies wrap will be the least of their > problems. > But the point of this patch is to catch jiffy wrap bugs in generic code as well as in platform-specific code. Doing it for 64-bit platforms as well will give us just that bit more testing coverage, and has no cost. (Well, 8 more bytes of kernel image...) ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] make jiffies wrap 5 min after boot 2003-02-16 6:56 ` Andrew Morton @ 2003-02-16 7:00 ` Andi Kleen 2003-02-16 8:10 ` Tim Schmielau 1 sibling, 0 replies; 12+ messages in thread From: Andi Kleen @ 2003-02-16 7:00 UTC (permalink / raw) To: Andrew Morton; +Cc: Andi Kleen, anton, linux-kernel, tim > But the point of this patch is to catch jiffy wrap bugs in generic code as > well as in platform-specific code. > > Doing it for 64-bit platforms as well will give us just that bit more testing > coverage, and has no cost. (Well, 8 more bytes of kernel image...) The 64bit platforms already have enough problems due to 64bit unclean code. No need to add a new unnecessary ones. Jiffie wrap is purely a 32bit problem, just like highmem. Please keep problems where they belong. -Andi ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] make jiffies wrap 5 min after boot 2003-02-16 6:56 ` Andrew Morton 2003-02-16 7:00 ` Andi Kleen @ 2003-02-16 8:10 ` Tim Schmielau 1 sibling, 0 replies; 12+ messages in thread From: Tim Schmielau @ 2003-02-16 8:10 UTC (permalink / raw) To: Anton Blanchard; +Cc: William Lee Irwin III, Andrew Morton, Andi Kleen, lkml Anton Blanchard <anton@samba.org> writes: > Hi, > > > +#define INITIAL_JIFFIES (0xffffffffUL & (unsigned long)(-300*HZ)) > > In order to make 64bit arches wrap too, you might want to use -1UL here. > Not that jiffies should wrap on a 64bit machine... The whole point of the "0xffffffffUL &" is not to test 64 bit arches, because I know Andi doesn't take jiffies wrap patches. And-ing with -1UL is a no-op, as it is with ~0UL. Tim ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH *] use 64 bit jiffies @ 2003-02-04 17:37 Randy.Dunlap 2003-02-16 1:37 ` [PATCH] make jiffies wrap 5 min after boot Tim Schmielau 0 siblings, 1 reply; 12+ messages in thread From: Randy.Dunlap @ 2003-02-04 17:37 UTC (permalink / raw) To: Denis Vlasenko; +Cc: Matti Aarnio, Tim Schmielau, lkml On Tue, 4 Feb 2003, Denis Vlasenko wrote: | On 3 February 2003 10:28, Matti Aarnio wrote: | > | > You don't need to have 64-bit jiffy for things like internal | > timers, nor for uptime tracking. | > | > Timers have well behaving constructs to use 32-bit jiffy quite | > successfully, and 64-bit values, especially atomicish, in 32-bit | > register-poor machines (i386) are damn difficult. | > | > I do have a number of machines with 100 to 300 day uptimes, all | > with "mere" 32-bit jiffy. With 1000 Hz clock that means at least | > one full wrap-around of jiffy. | | Your processes will show strange start times, CPU times etc. | This will happen in 2.5 pretty soon (after 50 days uptime). | | However, this is a bit cosmetic. There is a much more serious problem: | | Jiffy Wrap Bugs | | There were reports of machines hanging on jiffy wrap. | This is typically a result of incorrect jiffy use in some driver. | Ask Tim - he is hunting those problems regularly, but he is outnumbered | by buggy driver authors. :( | | There is a better solution to ensure correct jiffy wrap handling in | *ALL* kernel code: make jiffy wrap in first five minutes of uptime. | Tim has a patch for such config option. This is almost right. | This MUST NOT be a config option, it MUST be mandatory in every | kernel. Driver writers would be bitten by their own bugs and will | fix it themself. Tim, what do you think? I like it too. We should take advantage of easy-to-force/find/fix problems like this. -- ~Randy ^ permalink raw reply [flat|nested] 12+ messages in thread
* [PATCH] make jiffies wrap 5 min after boot 2003-02-04 17:37 [PATCH *] use 64 bit jiffies Randy.Dunlap @ 2003-02-16 1:37 ` Tim Schmielau 2003-02-16 2:08 ` Anton Blanchard 0 siblings, 1 reply; 12+ messages in thread From: Tim Schmielau @ 2003-02-16 1:37 UTC (permalink / raw) To: lkml; +Cc: Randy.Dunlap, Denis Vlasenko > | There is a better solution to ensure correct jiffy wrap handling in > | *ALL* kernel code: make jiffy wrap in first five minutes of uptime. > | Tim has a patch for such config option. This is almost right. > | This MUST NOT be a config option, it MUST be mandatory in every > | kernel. Driver writers would be bitten by their own bugs and will > | fix it themself. Tim, what do you think? > > I like it too. We should take advantage of easy-to-force/find/fix > problems like this. Ok, I've forward-ported the patch to 2.5. Since 2.5 isn't supposed to be stable anyways, I made it unconditional. Note that it is completely transparent to the user. Tim --- linux-2.5.61/include/linux/time.h Sat Feb 15 11:53:48 2003 +++ linux-2.5.61-jdbg/include/linux/time.h Sun Feb 16 01:42:26 2003 @@ -28,6 +28,12 @@ #include <linux/seqlock.h> /* + * Have the 32 bit jiffies value wrap 5 minutes after boot + * so jiffies wrap bugs show up earlier. + */ +#define INITIAL_JIFFIES (0xffffffffUL & (unsigned long)(-300*HZ)) + +/* * Change timeval to jiffies, trying to avoid the * most obvious overflows.. * --- linux-2.5.61/kernel/timer.c Sat Feb 15 11:53:49 2003 +++ linux-2.5.61-jdbg/kernel/timer.c Sun Feb 16 02:05:38 2003 @@ -755,7 +755,7 @@ } /* jiffies at the most recent update of wall time */ -unsigned long wall_jiffies; +unsigned long wall_jiffies = INITIAL_JIFFIES; /* * This read-write spinlock protects us from races in SMP while @@ -1098,7 +1098,7 @@ do { seq = read_seqbegin(&xtime_lock); - uptime = jiffies_64; + uptime = jiffies_64 - INITIAL_JIFFIES; do_div(uptime, HZ); val.uptime = (unsigned long) uptime; @@ -1174,6 +1174,13 @@ } for (j = 0; j < TVR_SIZE; j++) INIT_LIST_HEAD(base->tv1.vec + j); + + base->timer_jiffies = INITIAL_JIFFIES; + base->tv1.index = INITIAL_JIFFIES & TVR_MASK; + base->tv2.index = (INITIAL_JIFFIES >> TVR_BITS) & TVN_MASK; + base->tv3.index = (INITIAL_JIFFIES >> (TVR_BITS+TVN_BITS)) & TVN_MASK; + base->tv4.index = (INITIAL_JIFFIES >> (TVR_BITS+2*TVN_BITS)) & TVN_MASK; + base->tv5.index = (INITIAL_JIFFIES >> (TVR_BITS+3*TVN_BITS)) & TVN_MASK; } static int __devinit timer_cpu_notify(struct notifier_block *self, --- linux-2.5.61/fs/proc/array.c Sat Feb 15 11:54:54 2003 +++ linux-2.5.61-jdbg/fs/proc/array.c Sun Feb 16 01:58:26 2003 @@ -327,7 +327,8 @@ nice, 0UL /* removed */, jiffies_to_clock_t(task->it_real_value), - (unsigned long long) jiffies_64_to_clock_t(task->start_time), + (unsigned long long) + jiffies_64_to_clock_t(task->start_time - INITIAL_JIFFIES), vsize, mm ? mm->rss : 0, /* you might want to shift this left 3 */ task->rlim[RLIMIT_RSS].rlim_cur, --- linux-2.5.61/fs/proc/proc_misc.c Sat Feb 15 11:53:47 2003 +++ linux-2.5.61-jdbg/fs/proc/proc_misc.c Sun Feb 16 02:01:17 2003 @@ -104,7 +104,7 @@ unsigned long uptime_remainder; int len; - uptime = get_jiffies_64(); + uptime = get_jiffies_64() - INITIAL_JIFFIES; uptime_remainder = (unsigned long) do_div(uptime, HZ); #if HZ!=100 @@ -320,7 +320,7 @@ { int i, len; extern unsigned long total_forks; - u64 jif = get_jiffies_64(); + u64 jif = get_jiffies_64() - INITIAL_JIFFIES; unsigned int sum = 0, user = 0, nice = 0, system = 0, idle = 0, iowait = 0; for (i = 0 ; i < NR_CPUS; i++) { --- linux-2.5.61/arch/alpha/kernel/time.c Sat Feb 15 11:53:34 2003 +++ linux-2.5.61-jdbg/arch/alpha/kernel/time.c Sun Feb 16 01:42:26 2003 @@ -50,7 +50,7 @@ #include "proto.h" #include "irq_impl.h" -u64 jiffies_64; +u64 jiffies_64 = INITIAL_JIFFIES; extern unsigned long wall_jiffies; /* kernel/timer.c */ --- linux-2.5.61/arch/arm/kernel/time.c Sat Feb 15 11:53:34 2003 +++ linux-2.5.61-jdbg/arch/arm/kernel/time.c Sun Feb 16 01:42:26 2003 @@ -32,7 +32,7 @@ #include <asm/irq.h> #include <asm/leds.h> -u64 jiffies_64; +u64 jiffies_64 = INITIAL_JIFFIES; extern unsigned long wall_jiffies; --- linux-2.5.61/arch/cris/kernel/time.c Fri Jan 17 03:22:16 2003 +++ linux-2.5.61-jdbg/arch/cris/kernel/time.c Sun Feb 16 01:42:26 2003 @@ -45,7 +45,7 @@ #include <asm/svinto.h> -u64 jiffies_64; +u64 jiffies_64 = INITIAL_JIFFIES; static int have_rtc; /* used to remember if we have an RTC or not */ --- linux-2.5.61/arch/i386/kernel/time.c Sat Feb 15 11:53:34 2003 +++ linux-2.5.61-jdbg/arch/i386/kernel/time.c Sun Feb 16 01:42:26 2003 @@ -66,7 +66,7 @@ #include "do_timer.h" -u64 jiffies_64; +u64 jiffies_64 = INITIAL_JIFFIES; unsigned long cpu_khz; /* Detected as we calibrate the TSC */ --- linux-2.5.61/arch/ia64/kernel/time.c Sat Feb 15 11:53:35 2003 +++ linux-2.5.61-jdbg/arch/ia64/kernel/time.c Sun Feb 16 01:42:26 2003 @@ -27,7 +27,7 @@ extern unsigned long wall_jiffies; extern unsigned long last_time_offset; -u64 jiffies_64; +u64 jiffies_64 = INITIAL_JIFFIES; #ifdef CONFIG_IA64_DEBUG_IRQ --- linux-2.5.61/arch/m68k/kernel/time.c Sat Feb 15 11:53:35 2003 +++ linux-2.5.61-jdbg/arch/m68k/kernel/time.c Sun Feb 16 01:42:26 2003 @@ -26,7 +26,7 @@ #include <linux/timex.h> #include <linux/profile.h> -u64 jiffies_64; +u64 jiffies_64 = INITIAL_JIFFIES; static inline int set_rtc_mmss(unsigned long nowtime) { --- linux-2.5.61/arch/m68knommu/kernel/time.c Sat Feb 15 11:53:35 2003 +++ linux-2.5.61-jdbg/arch/m68knommu/kernel/time.c Sun Feb 16 01:42:26 2003 @@ -26,7 +26,7 @@ #define TICK_SIZE (tick_nsec / 1000) -u64 jiffies_64; +u64 jiffies_64 = INITIAL_JIFFIES; static inline int set_rtc_mmss(unsigned long nowtime) { --- linux-2.5.61/arch/mips/kernel/time.c Sat Feb 15 11:53:35 2003 +++ linux-2.5.61-jdbg/arch/mips/kernel/time.c Sun Feb 16 01:42:26 2003 @@ -32,7 +32,7 @@ #define USECS_PER_JIFFY (1000000/HZ) #define USECS_PER_JIFFY_FRAC ((1000000ULL << 32) / HZ & 0xffffffff) -u64 jiffies_64; +u64 jiffies_64 = INITIAL_JIFFIES; /* * forward reference --- linux-2.5.61/arch/parisc/kernel/time.c Sat Feb 15 11:53:35 2003 +++ linux-2.5.61-jdbg/arch/parisc/kernel/time.c Sun Feb 16 01:42:26 2003 @@ -32,7 +32,7 @@ #include <linux/timex.h> -u64 jiffies_64; +u64 jiffies_64 = INITIAL_JIFFIES; /* xtime and wall_jiffies keep wall-clock time */ extern unsigned long wall_jiffies; --- linux-2.5.61/arch/ppc/kernel/time.c Sat Feb 15 11:53:35 2003 +++ linux-2.5.61-jdbg/arch/ppc/kernel/time.c Sun Feb 16 01:42:26 2003 @@ -68,7 +68,7 @@ #include <asm/time.h> /* XXX false sharing with below? */ -u64 jiffies_64; +u64 jiffies_64 = INITIAL_JIFFIES; unsigned long disarm_decr[NR_CPUS]; --- linux-2.5.61/arch/ppc64/kernel/time.c Sat Feb 15 11:53:36 2003 +++ linux-2.5.61-jdbg/arch/ppc64/kernel/time.c Sun Feb 16 01:42:26 2003 @@ -65,7 +65,7 @@ void smp_local_timer_interrupt(struct pt_regs *); -u64 jiffies_64; +u64 jiffies_64 = INITIAL_JIFFIES; /* keep track of when we need to update the rtc */ time_t last_rtc_update; --- linux-2.5.61/arch/s390/kernel/time.c Sat Feb 15 11:53:36 2003 +++ linux-2.5.61-jdbg/arch/s390/kernel/time.c Sun Feb 16 01:42:26 2003 @@ -46,7 +46,7 @@ #define TICK_SIZE tick -u64 jiffies_64; +u64 jiffies_64 = INITIAL_JIFFIES; static ext_int_info_t ext_int_info_timer; static uint64_t xtime_cc; --- linux-2.5.61/arch/s390x/kernel/time.c Sat Feb 15 11:53:36 2003 +++ linux-2.5.61-jdbg/arch/s390x/kernel/time.c Sun Feb 16 01:42:26 2003 @@ -45,7 +45,7 @@ #define TICK_SIZE tick -u64 jiffies_64; +u64 jiffies_64 = INITIAL_JIFFIES; static ext_int_info_t ext_int_info_timer; static uint64_t xtime_cc; --- linux-2.5.61/arch/sh/kernel/time.c Sat Feb 15 11:53:36 2003 +++ linux-2.5.61-jdbg/arch/sh/kernel/time.c Sun Feb 16 01:42:26 2003 @@ -70,7 +70,7 @@ #endif /* CONFIG_CPU_SUBTYPE_ST40STB1 */ #endif /* __sh3__ or __SH4__ */ -u64 jiffies_64; +u64 jiffies_64 = INITIAL_JIFFIES; extern unsigned long wall_jiffies; #define TICK_SIZE tick --- linux-2.5.61/arch/sparc/kernel/time.c Sat Feb 15 11:53:36 2003 +++ linux-2.5.61-jdbg/arch/sparc/kernel/time.c Sun Feb 16 01:42:26 2003 @@ -45,7 +45,7 @@ extern unsigned long wall_jiffies; -u64 jiffies_64; +u64 jiffies_64 = INITIAL_JIFFIES; enum sparc_clock_type sp_clock_typ; spinlock_t mostek_lock = SPIN_LOCK_UNLOCKED; --- linux-2.5.61/arch/sparc64/kernel/time.c Sat Feb 15 11:53:36 2003 +++ linux-2.5.61-jdbg/arch/sparc64/kernel/time.c Sun Feb 16 01:42:26 2003 @@ -47,7 +47,7 @@ extern unsigned long wall_jiffies; -u64 jiffies_64; +u64 jiffies_64 = INITIAL_JIFFIES; static unsigned long mstk48t08_regs = 0UL; static unsigned long mstk48t59_regs = 0UL; --- linux-2.5.61/arch/v850/kernel/time.c Sat Feb 15 11:53:37 2003 +++ linux-2.5.61-jdbg/arch/v850/kernel/time.c Sun Feb 16 01:42:26 2003 @@ -25,7 +25,7 @@ #include "mach.h" -u64 jiffies_64; +u64 jiffies_64 = INITIAL_JIFFIES; #define TICK_SIZE (tick_nsec / 1000) --- linux-2.5.61/arch/x86_64/kernel/time.c Sat Feb 15 11:54:51 2003 +++ linux-2.5.61-jdbg/arch/x86_64/kernel/time.c Sun Feb 16 01:42:26 2003 @@ -30,7 +30,7 @@ #include <asm/apic.h> #endif -u64 jiffies_64; +u64 jiffies_64 = INITIAL_JIFFIES; extern int using_apic_timer; ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] make jiffies wrap 5 min after boot 2003-02-16 1:37 ` [PATCH] make jiffies wrap 5 min after boot Tim Schmielau @ 2003-02-16 2:08 ` Anton Blanchard 2003-02-16 2:43 ` William Lee Irwin III 0 siblings, 1 reply; 12+ messages in thread From: Anton Blanchard @ 2003-02-16 2:08 UTC (permalink / raw) To: Tim Schmielau; +Cc: lkml, Randy.Dunlap, Denis Vlasenko Hi, > +#define INITIAL_JIFFIES (0xffffffffUL & (unsigned long)(-300*HZ)) In order to make 64bit arches wrap too, you might want to use -1UL here. Not that jiffies should wrap on a 64bit machine... Anton ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] make jiffies wrap 5 min after boot 2003-02-16 2:08 ` Anton Blanchard @ 2003-02-16 2:43 ` William Lee Irwin III 2003-02-16 2:50 ` Michael Vergoz 2003-02-16 6:37 ` Robert Love 0 siblings, 2 replies; 12+ messages in thread From: William Lee Irwin III @ 2003-02-16 2:43 UTC (permalink / raw) To: Anton Blanchard; +Cc: Tim Schmielau, lkml, Randy.Dunlap, Denis Vlasenko At some point in the past, someone else wrote: >> +#define INITIAL_JIFFIES (0xffffffffUL & (unsigned long)(-300*HZ)) On Sun, Feb 16, 2003 at 01:08:08PM +1100, Anton Blanchard wrote: > In order to make 64bit arches wrap too, you might want to use -1UL here. > Not that jiffies should wrap on a 64bit machine... Can I get a vote for ~0UL instead of -1UL? -- wli ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] make jiffies wrap 5 min after boot 2003-02-16 2:43 ` William Lee Irwin III @ 2003-02-16 2:50 ` Michael Vergoz 2003-02-16 6:37 ` Robert Love 1 sibling, 0 replies; 12+ messages in thread From: Michael Vergoz @ 2003-02-16 2:50 UTC (permalink / raw) To: William Lee Irwin III, Anton Blanchard Cc: Tim Schmielau, lkml, Randy.Dunlap, Denis Vlasenko sure. rdgs Michael V Sent: Sunday, February 16, 2003 3:43 AM Subject: Re: [PATCH] make jiffies wrap 5 min after boot > At some point in the past, someone else wrote: > >> +#define INITIAL_JIFFIES (0xffffffffUL & (unsigned long)(-300*HZ)) > > On Sun, Feb 16, 2003 at 01:08:08PM +1100, Anton Blanchard wrote: > > In order to make 64bit arches wrap too, you might want to use -1UL here. > > Not that jiffies should wrap on a 64bit machine... > > Can I get a vote for ~0UL instead of -1UL? > > -- wli > - > 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/ > ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] make jiffies wrap 5 min after boot 2003-02-16 2:43 ` William Lee Irwin III 2003-02-16 2:50 ` Michael Vergoz @ 2003-02-16 6:37 ` Robert Love 2003-02-16 7:16 ` Muli Ben-Yehuda 1 sibling, 1 reply; 12+ messages in thread From: Robert Love @ 2003-02-16 6:37 UTC (permalink / raw) To: William Lee Irwin III Cc: Anton Blanchard, Tim Schmielau, lkml, Randy.Dunlap, Denis Vlasenko On Sat, 2003-02-15 at 21:43, William Lee Irwin III wrote: > Can I get a vote for ~0UL instead of -1UL? OK, I bite. What is the difference? Aren't both equivalent? Robert Love ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] make jiffies wrap 5 min after boot 2003-02-16 6:37 ` Robert Love @ 2003-02-16 7:16 ` Muli Ben-Yehuda 2003-02-16 11:50 ` Falk Hueffner 0 siblings, 1 reply; 12+ messages in thread From: Muli Ben-Yehuda @ 2003-02-16 7:16 UTC (permalink / raw) To: Robert Love; +Cc: lkml On Sun, Feb 16, 2003 at 01:37:40AM -0500, Robert Love wrote: > On Sat, 2003-02-15 at 21:43, William Lee Irwin III wrote: > > > Can I get a vote for ~0UL instead of -1UL? > > OK, I bite. What is the difference? Aren't both equivalent? I have no idea if that's what wli meant, but -1UL is only "all ones" in a 2's complement binary representation. -- Muli Ben-Yehuda http://www.mulix.org http://syscalltrack.sf.net ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] make jiffies wrap 5 min after boot 2003-02-16 7:16 ` Muli Ben-Yehuda @ 2003-02-16 11:50 ` Falk Hueffner 2003-02-16 12:04 ` William Lee Irwin III 0 siblings, 1 reply; 12+ messages in thread From: Falk Hueffner @ 2003-02-16 11:50 UTC (permalink / raw) To: lkml Muli Ben-Yehuda <mulix@mulix.org> writes: > On Sun, Feb 16, 2003 at 01:37:40AM -0500, Robert Love wrote: > > On Sat, 2003-02-15 at 21:43, William Lee Irwin III wrote: > > > > > Can I get a vote for ~0UL instead of -1UL? > > > > OK, I bite. What is the difference? Aren't both equivalent? > > I have no idea if that's what wli meant, but -1UL is only "all ones" > in a 2's complement binary representation. No. Wraparound of unsigned types is well-defined. -1UL must be the largest possible unsigned long value, which must consist of only 1 bits (except for possible padding bits). Of course, no machines with ones-complement (or padding bits, or integer trap representations, or any of the other ISO braindamages) exist, so this is mostly irrelevant anyway. -- Falk ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] make jiffies wrap 5 min after boot 2003-02-16 11:50 ` Falk Hueffner @ 2003-02-16 12:04 ` William Lee Irwin III 0 siblings, 0 replies; 12+ messages in thread From: William Lee Irwin III @ 2003-02-16 12:04 UTC (permalink / raw) To: Falk Hueffner; +Cc: lkml Muli Ben-Yehuda <mulix@mulix.org> writes: >> I have no idea if that's what wli meant, but -1UL is only "all ones" >> in a 2's complement binary representation. On Sun, Feb 16, 2003 at 12:50:34PM +0100, Falk Hueffner wrote: > No. Wraparound of unsigned types is well-defined. -1UL must be the > largest possible unsigned long value, which must consist of only 1 > bits (except for possible padding bits). > Of course, no machines with ones-complement (or padding bits, or > integer trap representations, or any of the other ISO braindamages) > exist, so this is mostly irrelevant anyway. In the "obvious" sense, -1UL is an oxymoron, as -1 is inherently signed, and the "UL" says "unsigned". It's aesthetic. It's a violation of what I consider good taste to do signed bit twiddling on an unsigned value and/or vice-versa. Regardless of what ISO and/or Linux may or may not support, the habits ingrained in me wrt. portability say the assumption must not be made. YMMV. -- wli ^ permalink raw reply [flat|nested] 12+ messages in thread
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2003-02-16 6:36 ` [PATCH] make jiffies wrap 5 min after boot Andi Kleen
2003-02-16 6:56 ` Andrew Morton
2003-02-16 7:00 ` Andi Kleen
2003-02-16 8:10 ` Tim Schmielau
2003-02-04 17:37 [PATCH *] use 64 bit jiffies Randy.Dunlap
2003-02-16 1:37 ` [PATCH] make jiffies wrap 5 min after boot Tim Schmielau
2003-02-16 2:08 ` Anton Blanchard
2003-02-16 2:43 ` William Lee Irwin III
2003-02-16 2:50 ` Michael Vergoz
2003-02-16 6:37 ` Robert Love
2003-02-16 7:16 ` Muli Ben-Yehuda
2003-02-16 11:50 ` Falk Hueffner
2003-02-16 12:04 ` William Lee Irwin III
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