-----Original Message----- From: Dietmar Eggemann [mailto:dietmar.eggemann@arm.com] Sent: Thursday, May 6, 2021 12:30 AM To: Song Bao Hua (Barry Song) <song.bao.hua@hisilicon.com>; Vincent Guittot <vincent.guittot@linaro.org> Cc: tim.c.chen@linux.intel.com; catalin.marinas@arm.com; will@kernel.org; rjw@rjwysocki.net; bp@alien8.de; tglx@linutronix.de; mingo@redhat.com; lenb@kernel.org; peterz@infradead.org; rostedt@goodmis.org; bsegall@google.com; mgorman@suse.de; msys.mizuma@gmail.com; valentin.schneider@arm.com; gregkh@linuxfoundation.org; Jonathan Cameron <jonathan.cameron@huawei.com>; juri.lelli@redhat.com; mark.rutland@arm.com; sudeep.holla@arm.com; aubrey.li@linux.intel.com; linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org; linux-acpi@vger.kernel.org; x86@kernel.org; xuwei (O) <xuwei5@huawei.com>; Zengtao (B) <prime.zeng@hisilicon.com>; guodong.xu@linaro.org; yangyicong <yangyicong@huawei.com>; Liguozhu (Kenneth) <liguozhu@hisilicon.com>; linuxarm@openeuler.org; hpa@zytor.com Subject: Re: [RFC PATCH v6 3/4] scheduler: scan idle cpu in cluster for tasks within one LLC
On 03/05/2021 13:35, Song Bao Hua (Barry Song) wrote:
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From: Song Bao Hua (Barry Song)
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From: Dietmar Eggemann [mailto:dietmar.eggemann@arm.com]
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On 29/04/2021 00:41, Song Bao Hua (Barry Song) wrote:
-----Original Message----- From: Dietmar Eggemann [mailto:dietmar.eggemann@arm.com]
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>>> From: Dietmar Eggemann [mailto:dietmar.eggemann@arm.com]
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>>> On 20/04/2021 02:18, Barry Song wrote:
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On the other hand, according to "sched: Implement smarter wake-affine logic"
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/ ?id=62470419
Proper factor in wake_wide is mainly beneficial of 1:n tasks like
postgresql/pgbench.
So using the smaller cluster size as factor might help make wake_affine false so improve pgbench.
From the commit log, while clients = 2*cpus, the commit made the biggest improvement. In my case, It should be clients=48 for a machine whose LLC size is 24.
In Linux, I created a 240MB database and ran "pgbench -c 48 -S -T 20 pgbench" under two different scenarios: 1. page cache always hit, so no real I/O for database read 2. echo 3 > /proc/sys/vm/drop_caches
For case 1, using cluster_size and using llc_size will result in similar tps= ~108000, all of 24 cpus have 100% cpu utilization.
For case 2, using llc_size still shows better performance.
tps for each test round(cluster size as factor in wake_wide): 1398.450887 1275.020401 1632.542437 1412.241627 1611.095692 1381.354294 1539.877146 avg tps = 1464
tps for each test round(llc size as factor in wake_wide): 1718.402983 1443.169823 1502.353823 1607.415861 1597.396924 1745.651814 1876.802168 avg tps = 1641 (+12%)
so it seems using cluster_size as factor in "slave >= factor && master >= slave * factor" isn't a good choice for my machine at least.
So SD size = 4 (instead of 24) seems to be too small for `-c 48`.
Just curious, have you seen the benefit of using wake wide on SD size = 24 (LLC) compared to not using it at all?
At least in my benchmark made today, I have not seen any benefit to use llc_size. Always returning 0 in wake_wide() seems to be much better. postgres@ubuntu:$pgbench -i pgbench postgres@pgbench:$ pgbench -T 120 -c 48 pgbench using llc_size, it got to 123tps always returning 0 in wake_wide(), it got to 158tps actually, I really couldn't reproduce the performance improvement the commit "sched: Implement smarter wake-affine logic" mentioned. on the other hand, the commit log didn't present the pgbench command parameter used. I guess the benchmark result will highly depend on the command parameter and disk I/O speed. Thanks Barry