RE: [PATCH v2] cpuidle: poll_state: Add time limit to poll_idle()

From: "Doug Smythies" <dsmythies@telus.net>
To: "'Rik van Riel'" <riel@surriel.com>,
	"'Rafael J. Wysocki'" <rjw@rjwysocki.net>
Cc: "'Linux PM'" <linux-pm@vger.kernel.org>,
	"'Frederic Weisbecker'" <fweisbec@gmail.com>,
	"'Thomas Gleixner'" <tglx@linutronix.de>,
	"'Paul McKenney'" <paulmck@linux.vnet.ibm.com>,
	"'Thomas Ilsche'" <thomas.ilsche@tu-dresden.de>,
	"'Aubrey Li'" <aubrey.li@linux.intel.com>,
	"'Mike Galbraith'" <mgalbraith@suse.de>,
	"'LKML'" <linux-kernel@vger.kernel.org>,
	"'Peter Zijlstra'" <peterz@infradead.org>,
	"Doug Smythies" <dsmythies@telus.net>
Subject: RE: [PATCH v2] cpuidle: poll_state: Add time limit to poll_idle()
Date: Thu, 22 Mar 2018 20:19:24 -0700	[thread overview]
Message-ID: <004c01d3c255$c1f146a0$45d3d3e0$@net> (raw)
In-Reply-To: z5HFe4V4W1Konz5chemDYc

On 2018.03.22 12:12 Doug Smythies wrote: 
>On 2018.03.22 09:32 Rik van Riel wrote:
>> On Wed, 2018-03-14 at 13:04 +0100, Peter Zijlstra wrote:
>>
>>> On x86 we don't have to use that time_check_counter thing,
>>> sched_clock()
>>> is really cheap, not sure if it makes sense on other platforms.
>>
>> Are you sure? I saw a 5-10% increase in CPU use,
>> for a constant query rate to a memcache style
>> workload, with v3 of this patch.
>
> I would very much like to be able to repeat your test results.
> However, I am not sure what you mean by "memcache style workload".
> Is there a test you can point me to? Say a Phoronix type test, for example.
>
> All of my tests with the V3 of this patch have been fine.

What is the difference between sched_clock() talked about herein,
and local_clock() used in the patch?

I'm not sure how good it is but I made a test. I didn't believe
the results, so I did it 3 times.

V7.3 is as from the git branch.
V7.3p is plus the patch adding the counter loop to poll_state.c

The test is a tight loop (about 19600 loops per second) running
on all 8 CPUs. I can not seem to get my system to use Idle State
0, so I disabled Idle States 1 and 2 to force use of Idle State 0.

V7.3 uses a processor package power of 62.5 Watts
V7.3p uses a processor package power of 53.4 Watts, or 14.6% less power.

The loop times do not change.
The Idle state 0 residency per unit time does not change.

... Doug