Messages in this thread Patch in this message | | | Date | Thu, 26 Feb 2004 15:06:22 -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 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.
-g
> > thanks > -john > > --- 1.5/include/linux/times.h Sun Nov 9 19:26:08 2003 > +++ edited/include/linux/times.h Wed Feb 25 17:39:11 2004 > @@ -7,7 +7,7 @@ > #include <asm/param.h> > > #if (HZ % USER_HZ)==0 > -# define jiffies_to_clock_t(x) ((x) / (HZ / USER_HZ)) > +# define jiffies_to_clock_t(x) (((x*TICK_NSEC*HZ)/NSEC_PER_SEC) / (HZ / USER_HZ)) > #else > # define jiffies_to_clock_t(x) ((clock_t) jiffies_64_to_clock_t((u64) x)) > #endif > > > > >
-- 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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