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

[Zachary Amsden <zach@vmware.com>]

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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