cpuset: Add cpuset.isolation_mask file
Add a new cpuset.isolation_mask file in order to be able to modify the
housekeeping cpumask for each individual isolation feature on runtime.
In the future this will include nohz_full, unbound timers,
unbound workqueues, unbound kthreads, managed irqs, etc...
Start with supporting domain exclusion and CPUs passed through
"isolcpus=".
The cpuset.isolation_mask defaults to 0. Setting it to 1 will exclude
the given cpuset from the domains (they will be attached to NULL domain).
As long as a CPU is part of any cpuset with cpuset.isolation_mask set to
1, it will remain isolated even if it overlaps with another cpuset that
has cpuset.isolation_mask set to 0. The same applies to parent and
subdirectories.
If a cpuset is a subset of "isolcpus=", it automatically maps it and
cpuset.isolation_mask will be set to 1. This subset is then cleared from
the initial "isolcpus=" mask. The user is then free to override
cpuset.isolation_mask to 0 in order to revert the effect of "isolcpus=".
Here is an example of use where the CPU 7 has been isolated on boot and
get re-attached to domains later from cpuset:
$ cat /proc/cmdline
isolcpus=7
$ cd /sys/fs/cgroup/cpuset
$ mkdir cpu7
$ cd cpu7
$ cat cpuset.cpus
0-7
$ cat cpuset.isolation_mask
0
$ ls /sys/kernel/debug/domains/cpu7 # empty because isolcpus=7
$ echo 7 > cpuset.cpus
$ cat cpuset.isolation_mask # isolcpus subset automatically mapped
1
$ echo 0 > cpuset.isolation_mask
$ ls /sys/kernel/debug/domains/cpu7/
domain0 domain1
CHECKME: Should we have individual cpuset.isolation.$feature files for
each isolation feature instead of a single mask file?
CHECKME: The scheduler is unhappy when _every_ CPUs are isolated
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Nitesh Lal <nilal@redhat.com>
Cc: Nicolas Saenz <nsaenzju@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Christoph Lameter <cl@gentwo.de>
Cc: Tejun Heo <tj@kernel.org>
Cc: Zefan Li <lizefan.x@bytedance.com>
Cc: Alex Belits <abelits@marvell.com>
1 file changed
