** Changed in: linux-lowlatency (Ubuntu Mantic)
Status: New => Fix Committed
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https://bugs.launchpad.net/bugs/2023007
Title:
kernel .config lowlatency improvements
Status in linux-lowlatency package in Ubuntu:
Fix Committed
Status in linux-lowlatency source package in Mantic:
Fix Committed
Bug description:
[Impact]
The lowlatency kernel in Ubuntu is specifically designed to prioritize
high responsiveness, making it ideal for multimedia environments like
DAWs and audio processing platforms, as well as soft real-time
environments.
With the introduction of a real-time kernel, it might be worth
reconsidering the role of the lowlatency kernel and potentially
including it as the default kernel in desktop images, focusing on its
suitability for desktop-oriented usage.
To achieve this, we can enable additional configuration settings and
make it more focused for a low-latency and highly responsive desktop
environment.
Optionally (for the future) provide also an additional user-space
package that would enable specific run-time kernel settings focused at
certain preset workload profiles (e.g, web navigation, gaming, audio
processing, etc.).
[Test case]
Use linux-lowlatency in a desktop environment and measure
responsiveness of interactive applications.
[Fix]
Enable the following additional .config settings to make this kernel
more suitable for a low-latency desktop kernel:
- 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 not 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 -
https://lore.kernel.org/lkml/20221016162305.2489629-3-j...@joelfernandes.org/)
[Regression potential]
Enabling all these settings can introduce a potential performance
regression, but the kernel should result more responsive and make it
more suitable for a desktop/multimedia/gaming/audio processing
context.
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