[Skiboot] [PATCH v2] slw: Modify the power9 stop0_lite latency & residency

Stewart Smith stewart at linux.vnet.ibm.com
Tue Aug 29 18:19:03 AEST 2017

Vaidyanathan Srinivasan <svaidy at linux.vnet.ibm.com> writes:
> From: "Gautham R. Shenoy" <ego at linux.vnet.ibm.com>
> Currently skiboot exposes the exit-latency for stop0_lite as 200ns and
> the target-residency to be 2us.
> However, the kernel cpu-idle infrastructure rounds up the latency to
> microseconds and lists the stop0_lite latency as 0us, putting it on
> par with snooze state. As a result, when the predicted latency is
> small (< 1us), cpuidle will select stop0_lite instead of snooze. The
> difference between these states is that snooze doesn't require an
> interrupt to exit from the state, but stop0_lite does. And the value
> 200ns doesn't include the interrupt latency.
> This shows up in the context_switch2 benchmark
> (http://ozlabs.org/~anton/junkcode/context_switch2.c) where the number
> of context switches per second with the stop0_lite disabled is found
> to be roughly 30% more than with stop0_lite enabled.


Merged to master as of 51974cab7c89504a4ceb6706437665d5e8d2a533.

Let's hope that helps.

Stewart Smith
OPAL Architect, IBM.

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