Enable Linux PSI metrics

[jacknagel]

What would you like to be added:
Enable kernel PSI metrics on EKS AMIs.

Why is this needed:
We would like to collect PSI metrics using node-exporter. This feature is present, but not enabled, on the latest EKS AMI:

$ cat /proc/pressure/cpu
cat: /proc/pressure/cpu: Operation not supported
$ uname -a
Linux ip-10-210-10-154.ec2.internal 5.4.110-54.182.amzn2.x86_64 #1 SMP Fri Apr 9 17:56:33 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
$ cat /boot/config-`uname -r` | grep PSI
CONFIG_PSI=y
CONFIG_PSI_DEFAULT_DISABLED=y

[lanxinyuchs]

"CONFIG_PSI_DEFAULT_DISABLED=y" means not enabled by default.

see the code implementation in "kernel/sched/psi.c" file:

#ifdef CONFIG_PSI_DEFAULT_DISABLED
static bool psi_enable;
#else
static bool psi_enable = true;
#endif
static int __init setup_psi(char *str)
{
	return kstrtobool(str, &psi_enable) == 0;
}
__setup("psi=", setup_psi);

Before Linux 5.6 (like 5.4), the proc entries for psi will be created no matter the "psi_enable" varible is true or false, but these entries could not be read or written.

After merging this commit(torvalds/linux@3d81768), the proc entries for psi will be created only when the "psi_enable" is true.

So for this case, you should add "psi=1" to the kernel command line to truly enable this feature, something like this:

grubby --args="psi=1" --update-kernel=/boot/vmlinuz-5.4.110-54.182.amzn2.x86_64

[ellistarn]

+1, this would be super nice for monitoring tools, especially when combined with cgroupsv2

[sidewinder12s]

@cartermckinnon Any update on if this can be enabled out of the box since we should be able to get something on the older kernel the AMI currently uses?

[cartermckinnon]

No concerns from me, tested with 1.24 (on the 5.4 kernel) and seems fine. Opened #1161 .