Re: Changing p_swtime and td_slptime to ticks

On Mon, Sep 17, 2007 at 05:05:57PM -0700, 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.

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.

Purely cosmetic request: please make the ticks and hz variables in the
libkvm/kvm_proc.c static. Or, even better, move it into the struct __kvm.

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Relevant Pages

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    ... set p_swtime and td_slptime which are used by the swapout/swapin code to select the appropriate thread to swap. ... 1/ the source of the ticks is a monotonically increasing count that never ... ULE does not have a once per-second loop iterating over all threads. ... 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. ...
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    ... properly set p_swtime and td_slptime which are used by the swapout/swapin code to select the appropriate thread to swap. ... 1/ the source of the ticks is a monotonically increasing count that never ... Really I think ticks would be the better metric in vm_glue.c but didn't want to make any drastic changes. ...
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  • Re: Changing p_swtime and td_slptime to ticks
    ... properly set p_swtime and td_slptime which are used by the swapout/swapin code to select the appropriate thread to swap. ... 1/ the source of the ticks is a monotonically increasing count that never ... Really I think ticks would be the better metric in vm_glue.c but didn't want to make any drastic changes. ...
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  • Re: Changing p_swtime and td_slptime to ticks
    ... set p_swtime and td_slptime which are used by the swapout/swapin code to select the appropriate thread to swap. ... 1/ the source of the ticks is a monotonically increasing count that never ... Really I think ticks would be the better metric in vm_glue.c but didn't want to make any drastic changes. ...
    (freebsd-arch)