[Bug 108700] 2x Media CPU power usage, or 15% perf drop when CPU bound GPU use-case is TDP limited

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=108700

--- Comment #13 from Lakshmi <lakshminarayana.vudum at intel.com> ---
Comments from Rafael J. Wysocki is added here

On 3/7/2019 2:00 PM, Vudum, Lakshminarayana wrote:
> Hi, Can you comment on this bug? Is your commit causing performance issues?

It shouldn't.

That said if reverting it causes the perf numbers to go up, then there is some
impact, but it can only be very indirect.

This commit only affects idle CPUs and what it does is to cause them to spend
less time doing idle polling in one go. Effectively, this may allow them to
enter real idle (non-polling) states more often and spend more time in
non-polling idle states overall.  If they are woken up from those idle states
(instead of just interrupting idle polling), you may see some increased latency
in very specific workloads.  Maybe the workload in question is one of these.

However, if it affects perf adversely, it will also improve energy-efficiency.

To verify, it might be instructive to run the workload under turbostat (as
"turbostat <command>") and compare the results with and without the commit in
question reverted.

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