[PATCH v4 0/2] rcu/nocb: Delete local variable 'need_rcu_nocb_mask' in rcu_init_nohz()

From: Zhen Lei
Date: Tue Aug 16 2022 - 21:43:37 EST


v3 --> v4:
Fix a build warning.
- struct cpumask *cpumask = NULL;
+ const struct cpumask *cpumask = NULL;

v2 --> v3:
1. Eliminate rcu_state.nocb_is_setup
2. Update the code based on the above patch and commit b37a667c6242
("rcu/nocb: Add an option to offload all CPUs on boot").

Test cases and test results as below:

----------------------------------------------------------------------
| CONFIG_NO_HZ_FULL | CONFIG_RCU_NOCB_CPU_DEFAULT_ALL | cmdline |
----------------------------------------------------------------------
1) N | N | none |
2) N | N | rcu_nocbs=1-2 |
3) Y | N | nohz_full=1-2 |
4) Y | Y | none |
----------------------------------------------------------------------

1)
[ 1085.691770] rcu-torture:--- End of test: SUCCESS: (default)
root@genericarmv8:~# dmesg | grep "Offload RCU callbacks"
[ 0.000000] rcu: Offload RCU callbacks from CPUs: (none).
root@genericarmv8:~# zcat /proc/config.gz | grep NOCB
CONFIG_RCU_NOCB_CPU=y
# CONFIG_RCU_NOCB_CPU_DEFAULT_ALL is not set
root@genericarmv8:~# zcat /proc/config.gz | grep NO_HZ_FULL
# CONFIG_NO_HZ_FULL is not set
root@genericarmv8:~# cat /proc/cmdline
console=ttyAMA0 root=/dev/vda2 crashkernel=256M@ee000000

2)
[ 1022.532198] rcu-torture:--- End of test: SUCCESS: (default)
root@genericarmv8:~# dmesg | grep "Offload RCU callbacks"
[ 0.000000] rcu: Offload RCU callbacks from CPUs: 1-2.
root@genericarmv8:~# zcat /proc/config.gz | grep NOCB
CONFIG_RCU_NOCB_CPU=y
# CONFIG_RCU_NOCB_CPU_DEFAULT_ALL is not set
root@genericarmv8:~# zcat /proc/config.gz | grep NO_HZ_FULL
# CONFIG_NO_HZ_FULL is not set
root@genericarmv8:~# cat /proc/cmdline
console=ttyAMA0 root=/dev/vda2 crashkernel=256M@ee000000 rcu_nocbs=1-2

3)
[ 1011.714712] rcu-torture:--- End of test: SUCCESS: (default)
root@genericarmv8:~# dmesg | grep "Offload RCU callbacks"
[ 0.000000] rcu: Offload RCU callbacks from CPUs: 1-2.
root@genericarmv8:~# zcat /proc/config.gz | grep NOCB
CONFIG_RCU_NOCB_CPU=y
# CONFIG_RCU_NOCB_CPU_DEFAULT_ALL is not set
root@genericarmv8:~# zcat /proc/config.gz | grep NO_HZ_FULL
CONFIG_NO_HZ_FULL=y
root@genericarmv8:~# cat /proc/cmdline
console=ttyAMA0 root=/dev/vda2 crashkernel=256M@ee000000 nohz_full=1-2

4)
[ 1031.047094] rcu-torture:--- End of test: SUCCESS: (default)
root@genericarmv8:~# dmesg | grep "Offload RCU callbacks"
[ 0.000000] rcu: Offload RCU callbacks from CPUs: 0-3.
root@genericarmv8:~# zcat /proc/config.gz | grep NOCB
CONFIG_RCU_NOCB_CPU=y
CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y
root@genericarmv8:~# zcat /proc/config.gz | grep NO_HZ_FULL
CONFIG_NO_HZ_FULL=y
root@genericarmv8:~# cat /proc/cmdline
console=ttyAMA0 root=/dev/vda2 crashkernel=256M@ee000000


v1 --> v2:
Update commit message.

Zhen Lei (2):
rcu: Eliminate rcu_state.nocb_is_setup
rcu: Simplify the code logic of rcu_init_nohz()

kernel/rcu/tree.h | 1 -
kernel/rcu/tree_nocb.h | 38 +++++++++++---------------------------
2 files changed, 11 insertions(+), 28 deletions(-)

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2.25.1