[PATCH 0/1][N/U] Enable lowlatency settings in the generic kernel

[Jay Vosburgh]

Andrea Righi <andrea.righi at canonical.com> wrote:

[...]
>- CONFIG_NO_HZ_FULL=y: enable access to "Full tickless mode" (shutdown
>  clock tick when possible across all the enabled CPUs if they are
>  either idle or running 1 task - reduce kernel jitter of running tasks
>  due to the periodic clock tick, must be enabled at boot time passing
>  `nohz_full=<cpu_list>`); this can actually help CPU-intensive
>  workloads and it could provide much more benefits than the CONFIG_HZ
>  difference (since it can potentially shutdown any kernel jitter on
>  specific CPUs), this one should really be enabled anyway, considering
>  that it is configurable at boot time

	FYI, we did some testing with CONFIG_NO_HZ_FULL=y as part of LP
1919154 [0].  The testing timed context switches, and did find some
additional overhead on AMD EPYC when NO_HZ_FULL is configured but not
enabled at boot.  This was on the Ubuntu 5.15 kernel, so, not the most
recent, but something to be aware of.  The test program is attached to
the bug.

	-J

[0] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154

---
	-Jay Vosburgh, jay.vosburgh at canonical.com