Re: [PATCH 1/3] Updated dynamic tick patches - Fix lost tick calculation in timer_pm.c

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Srivatsa Vaddagiri wrote:

On Wed, Aug 31, 2005 at 10:28:43PM +0530, Srivatsa Vaddagiri wrote:
Following patches related to dynamic tick are posted in separate mails,
for convenience of review. The first patch probably applies w/o dynamic
tick consideration also.

Patch 1/3  -> Fixup lost tick calculation in timer_pm.c

Currently, lost tick calculation in timer_pm.c is based on number
of microseconds that has elapsed since the last tick. Calculating
the number of microseconds is approximated by cyc2us, which
basically does :

	microsec = (cycles * 286) / 1024

Consider 10 ticks lost. This amounts to 14319*10 = 143190 cycles (14319 = PMTMR_EXPECTED_RATE/(CALIBRATE_LATCH/LATCH)). This amount to 39992 microseconds as per the above equation or 39992 / 4000 = 9 lost ticks, which is incorrect.

I feel lost ticks can be based on cycles difference directly
rather than being based on microseconds that has elapsed.

Following patch is in that direction.
With this patch, time had kept up really well on one particular
machine (Intel 4way Pentium 3 box) overnight, while
on another newer machine (Intel 4way Xeon with HT) it didnt do so
well (time sped up after 3 or 4 hours). Hence I consider this
particular patch will need more review/work.


Does this patch help address the issues pointed out here?

http://bugzilla.kernel.org/show_bug.cgi?id=5127
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