On Thu, 2004-02-26 at 16:20, George Anzinger wrote:
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
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));
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??
Finally got a chance to go through my work queue and yikes! This is
seriously stale! As neither George or I have come to bat with a patch,
I'll attempt a swing.
Albert/David: Would you mind testing the following to see if it resolves
the issue for you?
George: Mind skimming this to make sure its close enough to what you
diff -Nru a/include/linux/times.h b/include/linux/times.h
--- a/include/linux/times.h Tue Apr 13 15:00:25 2004
+++ b/include/linux/times.h Tue Apr 13 15:00:25 2004
@@ -7,7 +7,12 @@
#if (HZ % USER_HZ)==0
-# define jiffies_to_clock_t(x) ((x) / (HZ / USER_HZ))
+static inline long jiffies_to_clock_t(long x)
+ u64 tmp = (u64)x * TICK_NSEC;
+ x = do_div(tmp, (NSEC_PER_SEC / USER_HZ));
+ return (long)tmp;
# define jiffies_to_clock_t(x) ((clock_t) jiffies_64_to_clock_t((u64) x))