Changing p_swtime and td_slptime to ticks

[Julian Elischer]

Jeff Roberson wrote:
> Enclosed is a patch that fixes swapping with ULE.  ULE has never 
> properly set p_swtime and td_slptime which are used by the 
> swapout/swapin code to select the appropriate thread to swap.

I have not looked at in the depth required, but 2 points that I was unable
to check to my satisfaction before I got called away for work....

1/ the source of the ticks is a monotonically increasing count that never
goes backwards or changes?

2/ nothing that used to be accounted in seconds becomes accounted for in ticks?


> 
> In 4BSD these two variables are increment once per-second as schedcpu() 
> iterates over all threads.  ULE does not have a once per-second loop 
> iterating over all threads.  So I have changed p_swtime to p_swtick and 
> td_slptime to td_slptick.  These record the value of 'ticks' when the 
> thread slept or was last swapped in or out.
> 
> For backwards compatibility I leave the values in kinfo_proc with the 
> legacy meaning by subtracting from ticks and dividing by hz.  I perform 
> a similar transformation in the swapout code to convert to seconds.  
> This change does make it possible to use sub-second granular decisions 
> in the swap code, however I'm not sure if that's really necessary.
> 
> So that I did not disturb the 4BSD mechanism I kept the original 
> td_slptime in the td_sched area.  It should be possible to use 
> td_slptick directly but especially this close to release I did not want 
> to change 4BSD.
> 
> Feedback and testing welcome.
> 
> Thanks,
> Jeff
> 
> 
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