Re: [RFC v3 0/2] CPU-Idle latency selftest framework

From: Doug Smythies <dsmythies@telus.net>
To: Pratik Rajesh Sampat <psampat@linux.ibm.com>
Cc: rjw@rjwysocki.net, Daniel Lezcano <daniel.lezcano@linaro.org>,
	shuah@kernel.org, ego@linux.vnet.ibm.com, svaidy@linux.ibm.com,
	Linux PM list <linux-pm@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-kselftest@vger.kernel.org, pratik.r.sampat@gmail.com
Subject: Re: [RFC v3 0/2] CPU-Idle latency selftest framework
Date: Thu, 8 Apr 2021 22:23:38 -0700	[thread overview]
Message-ID: <CAAYoRsWaAmyuJU4FCb7gtK0y-ZprdDVvp0vMpy=ZohzoC7YX1Q@mail.gmail.com> (raw)
In-Reply-To: <20210404083354.23060-1-psampat@linux.ibm.com>

Hi Pratik,

I tried V3 on a Intel i5-10600K processor with 6 cores and 12 CPUs.
The core to cpu mappings are:
core 0 has cpus 0 and 6
core 1 has cpus 1 and 7
core 2 has cpus 2 and 8
core 3 has cpus 3 and 9
core 4 has cpus 4 and 10
core 5 has cpus 5 and 11

By default, it will test CPUs 0,2,4,6,10 on cores 0,2,4,0,2,4.
wouldn't it make more sense to test each core once?
With the source CPU always 0, I think the results from the results
from the destination CPUs 0 and 6, on core 0 bias the results, at
least in the deeper idle states. They don't make much difference in
the shallow states. Myself, I wouldn't include them in the results.
Example, where I used the -v option for all CPUs:

--IPI Latency Test---
--Baseline IPI Latency measurement: CPU Busy--
SRC_CPU   DEST_CPU IPI_Latency(ns)
0            0          101
0            1          790
0            2          609
0            3          595
0            4          737
0            5          759
0            6          780
0            7          741
0            8          574
0            9          681
0           10          527
0           11          552
Baseline Avg IPI latency(ns): 620  <<<< suggest 656 here
---Enabling state: 0---
SRC_CPU   DEST_CPU IPI_Latency(ns)
0            0           76
0            1          471
0            2          420
0            3          462
0            4          454
0            5          468
0            6          453
0            7          473
0            8          380
0            9          483
0           10          492
0           11          454
Expected IPI latency(ns): 0
Observed Avg IPI latency(ns) - State 0: 423 <<<<< suggest 456 here
---Enabling state: 1---
SRC_CPU   DEST_CPU IPI_Latency(ns)
0            0          112
0            1          866
0            2          663
0            3          851
0            4         1090
0            5         1314
0            6         1941
0            7         1458
0            8          687
0            9          802
0           10         1041
0           11         1284
Expected IPI latency(ns): 1000
Observed Avg IPI latency(ns) - State 1: 1009 <<<< suggest 1006 here
---Enabling state: 2---
SRC_CPU   DEST_CPU IPI_Latency(ns)
0            0           75
0            1        16362
0            2        16785
0            3        19650
0            4        17356
0            5        17606
0            6         2217
0            7        17958
0            8        17332
0            9        16615
0           10        17382
0           11        17423
Expected IPI latency(ns): 120000
Observed Avg IPI latency(ns) - State 2: 14730 <<<< suggest 17447 here
---Enabling state: 3---
SRC_CPU   DEST_CPU IPI_Latency(ns)
0            0          103
0            1        17416
0            2        17961
0            3        16651
0            4        17867
0            5        17726
0            6         2178
0            7        16620
0            8        20951
0            9        16567
0           10        17131
0           11        17563
Expected IPI latency(ns): 1034000
Observed Avg IPI latency(ns) - State 3: 14894 <<<< suggest 17645 here

Hope this helps.

... Doug