Messages in this thread | | | Date | Thu, 04 Aug 2005 09:45:55 -0700 | From | George Anzinger <> | Subject | Re: [UPDATE PATCH] push rounding up of relative request to schedule_timeout() |
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Uh... PLEASE tell me you are NOT changing timespec_to_jiffies() (and timeval_to_jiffies() to add 1. This is NOT the right thing to do. For repeating times (see setitimer code) we need the actual time as we KNOW where the jiffies edge is in the repeating case. The +1 is needed ONLY for the initial time, not the repeating time.
See: http://marc.theaimsgroup.com/?l=linux-kernel&m=112208357906156&w=2
George
Nishanth Aravamudan wrote: > On 03.08.2005 [17:51:47 -0700], Nishanth Aravamudan wrote: > >>On 03.08.2005 [16:20:57 +0200], Roman Zippel wrote: >> >>>Hi, >>> >>>On Mon, 1 Aug 2005, Nishanth Aravamudan wrote: >>> >>> >>>>+unsigned int __sched schedule_timeout_msecs(unsigned int timeout_msecs) >>>>+{ >>>>+ unsigned long expire_jifs; >>>>+ >>>>+ if (timeout_msecs == MAX_SCHEDULE_TIMEOUT_MSECS) { >>>>+ expire_jifs = MAX_SCHEDULE_TIMEOUT; >>>>+ } else { >>>>+ /* >>>>+ * msecs_to_jiffies() is a unit conversion, which truncates >>>>+ * (rounds down), so we need to add 1. >>>>+ */ >>>>+ expire_jifs = msecs_to_jiffies(timeout_msecs) + 1; >>>>+ } >>>>+ >>>>+ expire_jifs = schedule_timeout(expire_jifs); >>>>+ >>>>+ /* >>>>+ * don't need to add 1 here, even though there is truncation, >>>>+ * because we will add 1 if/when the value is sent back in >>>>+ */ >>>>+ return jiffies_to_msecs(expire_jifs); >>>>+} >>> >>>As I already mentioned for msleep_interruptible this is a really terrible >>>interface. >>>The "jiffies_to_msecs(msecs_to_jiffies(timeout_msecs) + 1)" case (when the >>>process is immediately woken up again) makes the caller suspectible to >>>timeout manipulations and requires constant reauditing, that no caller >>>gets it wrong, so it's better to avoid this error source completely. >> >>After some thought today, I realized the +1 case is not specific to >>milliseconds. It's just that it's only being done *correctly* in the >>milliseconds case...I think ;) > > > <snip> > >>Description: Ensure that schedule_timeout() requests can not possibly >>expire early in the timeout case, by adding the requested relative jiffy >>value to the next value of jiffies. Currently, by adding to the current >>value of jiffies, we might actually expire a jiffy too early (in a >>corner case). > > > Sorry, I forgot that sys_nanosleep() also always adds 1 to the request > (to account for this same issue, I believe, as POSIX demands no early > return from nanosleep() calls). There are some other locations where > similar > > + (t.tv_sec || t.tv_nsec) > > rounding-ups occur. I'll fix those separately if this patch goes in. I > change the one in sys_nanosleep() below to maintain the same latency as > we currently have. I also screwed up my layout in the previous > submission, sorry about that. > > Description: Ensure that schedule_timeout() requests can not possibly > expire early in the timeout case, by adding the requested relative jiffy > value to the next value of jiffies. Currently, by adding to the current > value of jiffies, we might actually expire a jiffy too early (in a > corner case). Modify the callers of schedule_timeout() in timer.c to not > add 1 themselves. > > Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com> > > --- > > timer.c | 13 +++++++------ > 1 files changed, 7 insertions(+), 6 deletions(-) > > --- 2.6.13-rc4-dev/kernel/timer.c 2005-08-01 12:31:53.000000000 -0700 > +++ 2.6.13-rc5/kernel/timer.c 2005-08-03 22:05:16.000000000 -0700 > @@ -1134,7 +1134,7 @@ fastcall signed long __sched schedule_ti > } > } > > - expire = timeout + jiffies; > + expire = timeout + jiffies + 1; > > init_timer(&timer); > timer.expires = expire; > @@ -1190,9 +1190,10 @@ unsigned int __sched schedule_timeout_ms > } else { > /* > * msecs_to_jiffies() is a unit conversion, which truncates > - * (rounds down), so we need to add 1. > + * (rounds down), so we need to add 1, but this is taken > + * care of by schedule_timeout() now. > */ > - expire_jifs = msecs_to_jiffies(timeout_msecs) + 1; > + expire_jifs = msecs_to_jiffies(timeout_msecs); > } > > expire_jifs = schedule_timeout(expire_jifs); > @@ -1286,7 +1287,7 @@ asmlinkage long sys_nanosleep(struct tim > if ((t.tv_nsec >= 1000000000L) || (t.tv_nsec < 0) || (t.tv_sec < 0)) > return -EINVAL; > > - expire = timespec_to_jiffies(&t) + (t.tv_sec || t.tv_nsec); > + expire = timespec_to_jiffies(&t); > current->state = TASK_INTERRUPTIBLE; > expire = schedule_timeout(expire); > > @@ -1675,7 +1676,7 @@ unregister_time_interpolator(struct time > */ > void msleep(unsigned int msecs) > { > - unsigned long timeout = msecs_to_jiffies(msecs) + 1; > + unsigned long timeout = msecs_to_jiffies(msecs); > > while (timeout) { > set_current_state(TASK_UNINTERRUPTIBLE); > @@ -1691,7 +1692,7 @@ EXPORT_SYMBOL(msleep); > */ > unsigned long msleep_interruptible(unsigned int msecs) > { > - unsigned long timeout = msecs_to_jiffies(msecs) + 1; > + unsigned long timeout = msecs_to_jiffies(msecs); > > while (timeout && !signal_pending(current)) { > set_current_state(TASK_INTERRUPTIBLE); > > - > 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/ >
-- George Anzinger george@mvista.com HRT (High-res-timers): http://sourceforge.net/projects/high-res-timers/ - 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/
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