linux-kernel - /proc/sys/kernel/sched_domain/, isolcpus, CONFIG_CPUMASK

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Date:   Fri, 15 Feb 2019 19:29:13 +0000
From:   "Rantala, Tommi T. (Nokia - FI/Espoo)" <tommi.t.rantala@...ia.com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "mingo@...hat.com" <mingo@...hat.com>
Subject: /proc/sys/kernel/sched_domain/, isolcpus, CONFIG_CPUMASK_OFFSTACK

Hello,

/proc/sys/kernel/sched_domain/ seems to be somewhat broken when kernel
is configured without CONFIG_CPUMASK_OFFSTACK and booting with
isolcpus= option.

Example with 8x CPU.

With CONFIG_CPUMASK_OFFSTACK=y and "isolcpus=2":

# uname -r
5.0.0-0.rc3.git0.1.fc30.x86_64

# ls /proc/sys/kernel/sched_domain/*
/proc/sys/kernel/sched_domain/cpu0:
domain0

/proc/sys/kernel/sched_domain/cpu1:
domain0

/proc/sys/kernel/sched_domain/cpu2:

/proc/sys/kernel/sched_domain/cpu3:
domain0

/proc/sys/kernel/sched_domain/cpu4:
domain0

/proc/sys/kernel/sched_domain/cpu5:
domain0

/proc/sys/kernel/sched_domain/cpu6:
domain0

/proc/sys/kernel/sched_domain/cpu7:
domain0


Another kernel without CONFIG_CPUMASK_OFFSTACK and "isolcpus=2", so
directories missing for CPUs 2-7:

# ls /proc/sys/kernel/sched_domain/
cpu0  cpu1

# ls /proc/sys/kernel/sched_domain/*
/proc/sys/kernel/sched_domain/cpu0:
domain0

/proc/sys/kernel/sched_domain/cpu1:
domain0


-Tommi