Very cool!
Can this heuristic be applied to C-State power domains as well?
Bill
On 10/07/08 16:55, Eric Saxe wrote:
> I've just been testing some changes I made to improve the PAD P-state
> transition policy.
>
> Before, PAD would ramp up the max speed as soon as the P-state domain
> went non-idle, and then ramp it back down the instant it goes idle again.
>
> Running this script on that kernel, focusing on an idle CPU:
>
> #!/usr/sbin/dtrace -s
>
> #pragma D option quiet
>
> ::ess_transition
> /curcpu->cpu_id == $1/
> {
> x++;
> }
>
> profile-1s
> /x > 0/
> {
> printf("%d\n", x);
> x = 0;
> }
>
> I would get ~140 transitions per second. With the new changes, we don't
> transition an idle P-state domain up to full speed until the first
> thread that begins running there either makes it through one time
> quantum, or transitions to another non-idle thread. This gets rid of the
> transitions we were doing simply as a result of transient background
> kernel activity, reducing the rate down to 2-4 transitions per
> second...and 0 per second once the domains are busy....
>
> -Eric
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