On 2016-10-28 00:29, Peter Zijlstra wrote:
On Fri, Oct 28, 2016 at 12:10:39AM -0700, Vikram Mulukutla wrote:
We propose Window-Assisted Load Tracking (WALT) as an alternative or
additional
load tracking scheme in lieu of or along with PELT, one that in our
estimation
better tracks task demand and CPU utilization especially for use cases
on
mobile devices. WALT was conceived by Srivatsa Vaddagiri to provide
better
perf-per-watt numbers on asymmetric CPU (frequency and/or IPC)
implementations,
(specifically on Qualcomm Snapgdragon chipsets running Android) and
its metrics
have been used to guide task placement and p-state selection (load
balancing
in CFS still uses PELT statistics). WALT is now present in the
android-common
kernel as well.
And how come we only learn of it after its already shipping? Isn't that
arse backwards?
Yes, but also we were not confident that it would be close to being
acceptable
upstream since it was intricately tied to our HMP scheduler. However now
that
more parties including the folks at ARM are interested, and given that
EAS
exists and schedutil was merged into mainline, we felt it the right time
to try and introduce the concept. In general we are seriously trying to
get
more things upstream and converge.
