ACK: [PATCH][M:lowlatency] UBUNTU: [Config] lowlatency: enhance desktop responsiveness

[Dimitri John Ledkov]

Ack, will apply to the upload I am preparing.

On Tue, 6 Jun 2023 at 09:03, Andrea Righi <andrea.righi at canonical.com> wrote:
>
> BugLink: https://bugs.launchpad.net/bugs/2023007
>
> Enable the following kernel configs to make the lowlatency kernel more
> suitable for a desktop-oriented context and give access to additional
> run-time / boot-time user-space settings:
>
>  - 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>`)
>
>  - CONFIG_RCU_NOCB_CPU=y, CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y: move RCU
>    callbacks from softirq context to kthread context (reduce time spent
>    in softirqs with preemption disabled to improve the overall system
>    responsiveness, at the cost of introducing a potential performance
>    penalty, because RCU callbacks are now processed by kernel threads)
>
>  - CONFIG_RCU_LAZY=y: batch RCU callbacks and then flush them after a
>    timed delay instead of executing them immediately (can provide 5~10%
>    power-savings for idle or lightly-loaded systems, this is extremely
>    useful for laptops / portable devices [1])
>
> [1] https://lore.kernel.org/lkml/20221016162305.2489629-3-joel@joelfernandes.org/
>
> Signed-off-by: Andrea Righi <andrea.righi at canonical.com>
> ---
>  debian.lowlatency/config/annotations | 24 ++++++++++++++++++++++--
>  1 file changed, 22 insertions(+), 2 deletions(-)
>
> diff --git a/debian.lowlatency/config/annotations b/debian.lowlatency/config/annotations
> index fef2202364bc..737a55be4ae2 100644
> --- a/debian.lowlatency/config/annotations
> +++ b/debian.lowlatency/config/annotations
> @@ -15,15 +15,35 @@ CONFIG_HZ_250                                   note<'Override default HZ used i
>  CONFIG_LATENCYTOP                               policy<{'amd64': 'y', 'arm64': 'y'}>
>  CONFIG_LATENCYTOP                               note<'https://lists.ubuntu.com/archives/kernel-team/2014-July/045006.html, LP#1655986'>
>
> +CONFIG_NO_HZ_FULL                               policy<{'amd64': 'y', 'arm64': 'y'}>
> +CONFIG_NO_HZ_FULL                               note<'Enable access to "Full tickless mode" (LP: #2023007)'>
> +
> +CONFIG_NO_HZ_IDLE                               policy<{'amd64': 'n', 'arm64': 'n'}>
> +CONFIG_NO_HZ_IDLE                               note<'Disabled in favor of CONFIG_NO_HZ_FULL (LP: #2023007)'>
> +
>  CONFIG_PREEMPT                                  policy<{'amd64': 'y', 'arm64': 'y'}>
> -CONFIG_PREEMPT                                  note<'Enable fully preemptible kernel'>
> +CONFIG_PREEMPT                                  note<'Enable fully preemptible kernel by default (can be changed at runtime via /sys/kernel/debug/sched/preempt)'>
>
>  CONFIG_PREEMPT_VOLUNTARY                        policy<{'amd64': 'n', 'arm64': 'n'}>
> -CONFIG_PREEMPT_VOLUNTARY                        note<'Disable voluntary preemption model'>
> +CONFIG_PREEMPT_VOLUNTARY                        note<'Disable voluntary preemption model by default (can be changed at runtime via /sys/kernel/debug/sched/preempt)'>
> +
> +CONFIG_RCU_LAZY                                 policy<{'amd64': 'y', 'arm64': 'y'}>
> +CONFIG_RCU_LAZY                                 note<'Batch RCU callbacks and then flush them after a timed delay instead of executing them immediately (LP: #2023007)'>
> +
> +CONFIG_RCU_NOCB_CPU                             policy<{'amd64': 'y', 'arm64': 'y'}>
> +CONFIG_RCU_NOCB_CPU                             note<'Move RCU callbacks from softirq context to kthread context (LP: #2023007)'>
> +
> +CONFIG_RCU_NOCB_CPU_DEFAULT_ALL                 policy<{'amd64': 'y', 'arm64': 'y'}>
> +CONFIG_RCU_NOCB_CPU_DEFAULT_ALL                 note<'Enable CONFIG_RCU_NOCB_CPU across all CPUs by default (LP: #2023007)'>
>
>
>  # ---- Annotations without notes ----
>
>  CONFIG_CC_VERSION_TEXT                          policy<{'amd64': '"x86_64-linux-gnu-gcc-12 (Ubuntu 12.3.0-1ubuntu1) 12.3.0"', 'arm64': '"aarch64-linux-gnu-gcc-12 (Ubuntu 12.3.0-1ubuntu1) 12.3.0"'}>
> +CONFIG_CONTEXT_TRACKING_USER                    policy<{'amd64': 'y', 'arm64': 'y'}>
> +CONFIG_CONTEXT_TRACKING_USER_FORCE              policy<{'amd64': 'n', 'arm64': 'n'}>
>  CONFIG_GCC_VERSION                              policy<{'amd64': '120300', 'arm64': '120300'}>
>  CONFIG_HZ                                       policy<{'amd64': '1000', 'arm64': '1000'}>
> +CONFIG_TICK_CPU_ACCOUNTING                      policy<{'amd64': '-', 'arm64': '-'}>
> +CONFIG_VIRT_CPU_ACCOUNTING                      policy<{'amd64': 'y', 'arm64': 'y'}>
> +CONFIG_VIRT_CPU_ACCOUNTING_GEN                  policy<{'amd64': 'y', 'arm64': 'y'}>
> --
> 2.39.2
>
>
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-- 
okurrr,

Dimitri