This bug was fixed in the package linux - 6.8.0-11.11
---------------
linux (6.8.0-11.11) noble; urgency=medium
* noble/linux: 6.8.0-11.11 -proposed tracker (LP: #2053094)
* Miscellaneous Ubuntu changes
- [Packaging] riscv64: disable building unnecessary binary debs
-- Paolo Pisati <paolo.pis...@canonical.com> Wed, 14 Feb 2024 00:04:31
+0100
** Changed in: linux (Ubuntu Noble)
Status: New => Fix Released
** Changed in: linux-lowlatency (Ubuntu Noble)
Status: New => Fix Released
--
You received this bug notification because you are a member of Kernel
Packages, which is subscribed to linux in Ubuntu.
https://bugs.launchpad.net/bugs/2045492
Title:
make lazy RCU a boot time option
Status in linux package in Ubuntu:
Fix Released
Status in linux-lowlatency package in Ubuntu:
Fix Released
Status in linux source package in Noble:
Fix Released
Status in linux-lowlatency source package in Noble:
Fix Released
Bug description:
[Impact]
With LP: #2023007 we have decided to enable CONFIG_RCU_LAZY in the
lowlatency kernel to improve power consumption, but this option can
potentially introduce performance regressions in some cases, due to
the fact that RCU callbacks are now batched and flushed all at once
after a timed delay.
It would be definitely safer to have a way to enable/disable lazy RCUs
at boot time. In this way we could provide a simple kernel command
line option that can be used in all those cases where the lowlatency
kernel is required, but we don't want to risk performance regressions.
[Test case]
In this context providing a single test case is not relevant. After
applying the fix any performance benchmark can be used to evaluate if
lazy RCU feature should be enabled at boot time or not (according to
the specific context where the lowlatency kernel is going to be
used/deployed).
[Fix]
Apply this patch to the *generic* kernel:
https://lore.kernel.org/lkml/20231203011252.233748-1-qyou...@layalina.io/T/#u
We want to apply this to the generic kernel, not just lowlatency,
because in this way *all* derivatives will have the possibility to get
this feature, in case some of them want to enable lazy RCUs (even
generic itself).
Then make sure that lowlatency (or any other kernel with
CONFIG_RCU_LAZY=y) also has CONFIG_RCU_LAZY_DEFAULT_OFF not set (so
that the previous behavior is not changed).
[Regression potential]
We may receive reports of small performance regressions vs power
consumption regressions, depending on the rcutree.enable_rcu_lazy
command line option that is used. In such case we should suggest the
user to test both with lazy RCU disabled or enabled.
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2045492/+subscriptions
--
Mailing list: https://launchpad.net/~kernel-packages
Post to : kernel-packages@lists.launchpad.net
Unsubscribe : https://launchpad.net/~kernel-packages
More help : https://help.launchpad.net/ListHelp
