Messages in this thread | | | Date | Thu, 26 Feb 2004 16:20:43 -0800 | From | George Anzinger <> | Subject | Re: /proc or ps tools bug? 2.6.3, time is off |
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john stultz wrote: > On Thu, 2004-02-26 at 15:06, George Anzinger wrote: > >>john stultz wrote: >> >>>On Wed, 2004-02-25 at 13:10, George Anzinger wrote: >>> >>> >>>>Albert Cahalan wrote: >>>> >>>> >>>>>This is NOT sane. Remeber that procps doesn't get to see HZ. >>>>>Only USER_HZ is available, as the AT_CLKTCK ELF note. >>>>> >>>>>I think the way to fix this is to skip or add a tick >>>>>every now and then, so that the long-term HZ is exact. >>>>> >>>>>Another way is to simply choose between pure old-style >>>>>tick-based timekeeping and pure new-style cycle-based >>>>>(TSC or ACPI) timekeeping. Systems with uncooperative >>>>>hardware have to use the old-style time keeping. This >>>>>should simply the code greatly. >>>> >>>>On checking the code and thinking about this, I would suggest that we change >>>>start_time in the task struct to be the wall time (or monotonic time if that >>>>seems better). I only find two places this is used, in proc and in the >>>>accounting code. Both of these could easily be changed. Of course, even >>>>leaving it as it is, they could be changed to report more correct values by >>>>using the correct conversions to translate the system HZ to USER_HZ. >>> >>> >>>Is this close to what your thinking of? >>>I can't reproduce the issue on my systems, so I'll need someone else to >>>test this. >> >>More or less. I wonder if: > > >>static inline long jiffies_to_clock_t(long x) >>{ >> u64 tmp = (u64)x * TICK_NSEC; >> div64(tmp, (NSEC_PER_SEC / USER_HZ)); >> return (long)x; >>} >>might be better as it addresses the overflow issue. Should be able to toss the >>#if (HZ % USER_HZ)==0 test too. We could get carried away and do scaled math to >>eliminate the div64 but I don't think this path is used enough to justify the >>clarity ;) that would make. > > > Sounds good to me. Would you mind sending the diff so Petri and David > could test it?
Oops, I have been caught :) The above was composed in the email window. I don't have a 2.6.x kernel up at the moment and I don't have any free cycles... Late next week?? >
-- George Anzinger george@mvista.com High-res-timers: http://sourceforge.net/projects/high-res-timers/ Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml
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