Changing p_swtime and td_slptime to ticks

[Jeff Roberson]

On Tue, 18 Sep 2007, Andre Oppermann wrote:

> Jeff Roberson wrote:
>> On Mon, 17 Sep 2007, Julian Elischer wrote:
>> 
>>> 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?
>> 
>> ticks is incremented each time hardclock() is called.  That's it.
>> 
>>> 
>>> 2/ nothing that used to be accounted in seconds becomes accounted for in 
>>> ticks?
>> 
>> I scale back to seconds where it is required.  Really I think ticks would 
>> be the better metric in vm_glue.c but didn't want to make any drastic 
>> changes.
>
> ticks is 2^31 on x86 and at HZ=1000 is wraps within a reasonable
> short uptime.  You have to make sure that your code handles that
> correctly or you run into lots of strange effects which are almost
> impossible to reproduce.  In TCP we've got bitten by that.

Thanks Andre, this is a good point.  For the td_slptime I don't think it's 
of practical concern.  However, for swtime I think I will convert it then 
to seconds from boot.

Jeff

>
> -- 
> Andre
>