RE: [PATCH] cpufreq: intel_pstate: Implement passive mode with HWP enabled

From: "Doug Smythies" <dsmythies@telus.net>
To: "'Rafael J. Wysocki'" <rjw@rjwysocki.net>
Cc: "'Linux Documentation'" <linux-doc@vger.kernel.org>,
	"'LKML'" <linux-kernel@vger.kernel.org>,
	"'Peter Zijlstra'" <peterz@infradead.org>,
	"'Srinivas Pandruvada'" <srinivas.pandruvada@linux.intel.com>,
	"'Giovanni Gherdovich'" <ggherdovich@suse.cz>,
	"'Francisco Jerez'" <francisco.jerez.plata@intel.com>,
	"'Linux PM'" <linux-pm@vger.kernel.org>
Subject: RE: [PATCH] cpufreq: intel_pstate: Implement passive mode with HWP enabled
Date: Wed, 15 Jul 2020 13:39:29 -0700	[thread overview]
Message-ID: <000f01d65ae8$0c607990$25216cb0$@net> (raw)
In-Reply-To: <3955470.QvD6XneCf3@kreacher>

On 2020.07.14 11:16 Rafael J. Wysocki wrote:
> 
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
...
> Since the passive mode hasn't worked with HWP at all, and it is not going to
> the default for HWP systems anyway, I don't see any drawbacks related to making
> this change, so I would consider this as 5.9 material unless there are any
> serious objections.

Good point.
Some of the tests I do involve labour intensive post processing of data.
I want to automate some of that work, and it will take time.
We might be into the 5.9-rc series before I have detailed feedback.

However, so far:

Inverse impulse response test [1]:

High level test, i5-9600K, HWP-passive (this patch), ondemand:
3101 tests. 0 failures. (GOOD)

From [1], re-stated:
> . High level: i5-9600K: 2453 tests, 60 failures, 2.45% fail rate. (HWP-active - powersave)
> . Verify acpi-cpufreq/ondemand works fine: i5-9600K: 8975 tests. 0 failures.

My version of that cool Alexander named pipe test [2] serialized workflow:

HWP-passive (this patch), performance: PASS.

From [2], re-stated, and also re-tested.
HWP-disabled passive - performance: FAIL.
Although, I believe the issue to be EPB management, [3].

And yes, I did see the reply to [3] that came earlier,
And have now re-done the test, with the referenced patch added.
It still is FAIL. I reply to the [3] thread, eventually.

[1] https://marc.info/?l=linux-pm&m=159354421400342&w=2
[2] https://marc.info/?l=linux-pm&m=159155067328641&w=2
[3] https://marc.info/?l=linux-pm&m=159438804230744&w=2

Kernel:

b08284a541ad (HEAD -> k58rc5-doug) cpufreq: intel_pstate: Avoid enabling HWP if EPP is not supported
063fd7ccabfe cpufreq: intel_pstate: Implement passive mode with HWP enabled
730ccf5054e9 cpufreq: intel_pstate: Allow raw energy performance preference value
bee36df01c68 cpufreq: intel_pstate: Allow enable/disable energy efficiency
199629d8200e cpufreq: intel_pstate: Fix active mode setting from command line
11ba468877bb (tag: v5.8-rc5, origin/master, origin/HEAD, master) Linux 5.8-rc5

Rules for this work:

. never use x86_energy_perf_policy.
. For HWP disabled: never change from active to passive or via versa, but rather do it via boot.
. after boot always check and reset the various power limit log bits that are set.
. never compile the kernel (well, until after any tests), which will set those bits again.
. never run prime95 high heat torture test, which will set those bits again.
. try to never do anything else that will set those bits again.

To be clear, I do allow changing governors within the context of the above rules.

... Doug