linux-kernel - Re: [RFC PATCH] sched/fair: Make tg->load

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Date:   Wed, 29 Mar 2023 14:36:44 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Aaron Lu <aaron.lu@...el.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Tim Chen <tim.c.chen@...el.com>,
        Nitin Tekchandani <nitin.tekchandani@...el.com>,
        Waiman Long <longman@...hat.com>,
        Yu Chen <yu.c.chen@...el.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] sched/fair: Make tg->load_avg per node

On 28/03/2023 14:56, Aaron Lu wrote:
> Hi Dietmar,
> 
> Thanks for taking a look.
> 
> On Tue, Mar 28, 2023 at 02:09:39PM +0200, Dietmar Eggemann wrote:
>> On 27/03/2023 07:39, Aaron Lu wrote:

[...]

> Did you test with a v6.3-rc based kernel?
> I encountered another problem on those kernels and had to temporarily use
> a v6.2 based kernel, maybe you have to do the same:
> https://lore.kernel.org/lkml/20230327080502.GA570847@ziqianlu-desk2/

No, I'm also on v6.2.

>> Is your postgres/sysbench running in a cgroup with cpu controller
>> attached? Mine isn't.
> 
> Yes, I had postgres and sysbench running in the same cgroup with cpu
> controller enabled. docker created the cgroup directory under
> /sys/fs/cgroup/system.slice/docker-XXX and cgroup.controllers has cpu
> there.

I'm running postgresql service directly on the machine. I boot now with
'cgroup_no_v1=all systemd.unified_cgroup_hierarchy=1' so I can add the
cpu controller to:

  system.slice/system-postgresql.slice/postgresql@...main.service

where the 96 postgres threads run and to

  user.slice/user-1005.slice/session-4.scope

where the 96 sysbench threads run.

Checked with systemd-cgls and `cat /sys/kernel/debug/sched/debug` that
those threads are really running there.

Still not seeing `update_load_avg` or `update_cfs_group` in perf report,
only some very low values for `update_blocked_averages`.

Also added CFS BW throttling to both cgroups. No change.

Then I moved session-4.scope's shell into `postgresql@...main.service`
so that `postgres` and `sysbench` threads run in the same cgroup.

Didn't change much.

>> Maybe I'm doing something else differently?
> 
> Maybe, you didn't mention how you started postgres, if you start it from
> the same session as sysbench and if autogroup is enabled, then all those
> tasks would be in the same autogroup taskgroup then it should have the
> same effect as my setup.

This should be now close to my setup running `postgres` and `sysbench`
in `postgresql@...main.service`.

> Anyway, you can try the following steps to see if you can reproduce this
> problem on your Arm64 server:
> 
> 1 docker pull postgres
> 2 sudo docker run --rm --name postgres-instance -e POSTGRES_PASSWORD=mypass -e POSTGRES_USER=sbtest -d postgres -c shared_buffers=80MB -c max_connections=250
> 3 go inside the container
>   sudo docker exec -it $the_just_started_container_id bash
> 4 install sysbench inside container
>   apt update and apt install sysbench
> 5 prepare
>   root@...tainer:/# sysbench --db-driver=pgsql --pgsql-user=sbtest --pgsql_password=mypass --pgsql-db=sbtest --pgsql-port=5432 --tables=16 --table-size=10000 --threads=224 --time=60 --report-interval=2 /usr/share/sysbench/oltp_read_only.lua prepare
> 6 run
>   root@...tainer:/# sysbench --db-driver=pgsql --pgsql-user=sbtest --pgsql_password=mypass --pgsql-db=sbtest --pgsql-port=5432 --tables=16 --table-size=10000 --threads=224 --time=60 --report-interval=2 /usr/share/sysbench/oltp_read_only.lua run

I would have to find time to learn how to set up docker on my machine
... But I use very similar values for the setup and sysbench test.

> Note that I used 224 threads where this problem is visible. I also tried
> 96 and update_cfs_group() and update_load_avg() cost about 1% cycles then.

True, I was hopping to see at least the 1% ;-)