64bit ticks, was Re: Changing p_swtime and td_slptime to ticks

On Tue, 18 Sep 2007, Jeff Roberson wrote:

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.

Is there a good reason for not making ticks 64bit? math involving this value is relatively infrequent. Bruce? Any comments? It'd sure let us forget all of these counter wrapping problems.

Thanks,
Jeff


Jeff


--
Andre

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Relevant Pages

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