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