This is a note to let you know that I've just added the patch titled sched/rt: Disable RT_RUNTIME_SHARE by default to the 5.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: sched-rt-disable-rt_runtime_share-by-default.patch and it can be found in the queue-5.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 2586af1ac187f6b3a50930a4e33497074e81762d Mon Sep 17 00:00:00 2001 From: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx> Date: Mon, 21 Sep 2020 16:39:49 +0200 Subject: sched/rt: Disable RT_RUNTIME_SHARE by default From: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx> commit 2586af1ac187f6b3a50930a4e33497074e81762d upstream. The RT_RUNTIME_SHARE sched feature enables the sharing of rt_runtime between CPUs, allowing a CPU to run a real-time task up to 100% of the time while leaving more space for non-real-time tasks to run on the CPU that lend rt_runtime. The problem is that a CPU can easily borrow enough rt_runtime to allow a spinning rt-task to run forever, starving per-cpu tasks like kworkers, which are non-real-time by design. This patch disables RT_RUNTIME_SHARE by default, avoiding this problem. The feature will still be present for users that want to enable it, though. Signed-off-by: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Tested-by: Wei Wang <wvw@xxxxxxxxxx> Link: https://lkml.kernel.org/r/b776ab46817e3db5d8ef79175fa0d71073c051c7.1600697903.git.bristot@xxxxxxxxxx Signed-off-by: Mark-PK Tsai <mark-pk.tsai@xxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- kernel/sched/features.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/kernel/sched/features.h +++ b/kernel/sched/features.h @@ -77,7 +77,7 @@ SCHED_FEAT(WARN_DOUBLE_CLOCK, false) SCHED_FEAT(RT_PUSH_IPI, true) #endif -SCHED_FEAT(RT_RUNTIME_SHARE, true) +SCHED_FEAT(RT_RUNTIME_SHARE, false) SCHED_FEAT(LB_MIN, false) SCHED_FEAT(ATTACH_AGE_LOAD, true) Patches currently in stable-queue which might be from bristot@xxxxxxxxxx are queue-5.4/sched-rt-disable-rt_runtime_share-by-default.patch