* [PATCH v6 0/2] rcu/nocb: Delete local variable 'need_rcu_nocb_mask' in rcu_init_nohz()
@ 2022-09-01 13:14 Zhen Lei
2022-09-01 13:14 ` [PATCH v6 1/2] rcu: Simplify rcu_init_nohz() cpumask handling Zhen Lei
2022-09-01 13:14 ` [PATCH v6 2/2] rcu: Offload callback processing from all CPUs in the absence of rcu_nocbs= Zhen Lei
0 siblings, 2 replies; 7+ messages in thread
From: Zhen Lei @ 2022-09-01 13:14 UTC (permalink / raw)
To: Paul E . McKenney, Frederic Weisbecker, Neeraj Upadhyay,
Josh Triplett, Steven Rostedt, Mathieu Desnoyers, Lai Jiangshan,
Joel Fernandes, rcu, linux-kernel
Cc: Zhen Lei
v5 --> v6:
1. Frist, update patch 1/2, so that, CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y takes
effect only when there are no 'rcu_nocbs=' and 'nohz_full='. Retain the same
semantics as the original.
2. Then, add patch 2/2, so that, CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y takes effect
as long as there is no "rcu_nocbs=" boot parameter. This is suggested by
Frederic Weisbecker.
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=2-3 |
4) Y | N | rcu_nocbs=1 nohz_full=3 |
5) Y | Y | none |
6) Y | Y | rcu_nocbs=1-2 |
7) Y | Y | nohz_full=2-3 |
8) Y | Y | rcu_nocbs=1 nohz_full=3 |
----------------------------------------------------------------------
dmesg | grep "Offload RCU callbacks"
1) none
2) Offload RCU callbacks from CPUs: 1-2.
3) Offload RCU callbacks from CPUs: 2-3.
4) Offload RCU callbacks from CPUs: 1,3.
5) Offload RCU callbacks from CPUs: 0-3.
6) Offload RCU callbacks from CPUs: 1-2.
7) Offload RCU callbacks from CPUs: 0-3.
8) Offload RCU callbacks from CPUs: 1,3.
v4 --> v5:
1. Cancel eliminate rcu_state.nocb_is_setup. It is useful for case 1) below.
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)
[ 1018.082417] rcu-torture:--- End of test: SUCCESS (default)
root@genericarmv8:~# dmesg | grep "Offload RCU callbacks"
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=ttyS0 earlyprintk=serial root=/dev/sda rw
2) 3) 4)
The same to v4.
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: Simplify rcu_init_nohz() cpumask handling
rcu: Offload callback processing from all CPUs in the absence of
rcu_nocbs=
kernel/rcu/Kconfig | 4 ++--
kernel/rcu/tree_nocb.h | 35 ++++++++++++-----------------------
2 files changed, 14 insertions(+), 25 deletions(-)
--
2.25.1
^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH v6 1/2] rcu: Simplify rcu_init_nohz() cpumask handling
2022-09-01 13:14 [PATCH v6 0/2] rcu/nocb: Delete local variable 'need_rcu_nocb_mask' in rcu_init_nohz() Zhen Lei
@ 2022-09-01 13:14 ` Zhen Lei
2022-09-01 13:25 ` Leizhen (ThunderTown)
2022-09-07 11:04 ` Frederic Weisbecker
2022-09-01 13:14 ` [PATCH v6 2/2] rcu: Offload callback processing from all CPUs in the absence of rcu_nocbs= Zhen Lei
1 sibling, 2 replies; 7+ messages in thread
From: Zhen Lei @ 2022-09-01 13:14 UTC (permalink / raw)
To: Paul E . McKenney, Frederic Weisbecker, Neeraj Upadhyay,
Josh Triplett, Steven Rostedt, Mathieu Desnoyers, Lai Jiangshan,
Joel Fernandes, rcu, linux-kernel
Cc: Zhen Lei
In kernels built with either CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y or
CONFIG_NO_HZ_FULL=y, additional CPUs must be added to rcu_nocb_mask.
Except that kernels booted without the rcu_nocbs= will not have
allocated rcu_nocb_mask. And the current rcu_init_nohz() function uses
its need_rcu_nocb_mask and offload_all local variables to track the
rcu_nocb and nohz_full state.
But there is a much simpler approach, namely creating a cpumask pointer
to track the default and then using cpumask_available() to check the
rcu_nocb_mask state. This commit takes this approach, thereby simplifying
and shortening the rcu_init_nohz() function.
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
kernel/rcu/tree_nocb.h | 35 ++++++++++++-----------------------
1 file changed, 12 insertions(+), 23 deletions(-)
diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index 0a5f0ef41484518..8b6dceeabde0b4d 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -1210,45 +1210,34 @@ EXPORT_SYMBOL_GPL(rcu_nocb_cpu_offload);
void __init rcu_init_nohz(void)
{
int cpu;
- bool need_rcu_nocb_mask = false;
- bool offload_all = false;
struct rcu_data *rdp;
-
-#if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL)
- if (!rcu_state.nocb_is_setup) {
- need_rcu_nocb_mask = true;
- offload_all = true;
- }
-#endif /* #if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL) */
+ const struct cpumask *cpumask = NULL;
#if defined(CONFIG_NO_HZ_FULL)
- if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask)) {
- need_rcu_nocb_mask = true;
- offload_all = false; /* NO_HZ_FULL has its own mask. */
- }
-#endif /* #if defined(CONFIG_NO_HZ_FULL) */
+ if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask))
+ cpumask = tick_nohz_full_mask;
+#endif
+
+#if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL)
+ if (!rcu_state.nocb_is_setup && !cpumask)
+ cpumask = cpu_possible_mask;
+#endif
- if (need_rcu_nocb_mask) {
+ if (cpumask) {
if (!cpumask_available(rcu_nocb_mask)) {
if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
return;
}
}
+
+ cpumask_or(rcu_nocb_mask, rcu_nocb_mask, cpumask);
rcu_state.nocb_is_setup = true;
}
if (!rcu_state.nocb_is_setup)
return;
-#if defined(CONFIG_NO_HZ_FULL)
- if (tick_nohz_full_running)
- cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
-#endif /* #if defined(CONFIG_NO_HZ_FULL) */
-
- if (offload_all)
- cpumask_setall(rcu_nocb_mask);
-
if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n");
cpumask_and(rcu_nocb_mask, cpu_possible_mask,
--
2.25.1
^ permalink raw reply related [flat|nested] 7+ messages in thread
* [PATCH v6 2/2] rcu: Offload callback processing from all CPUs in the absence of rcu_nocbs=
2022-09-01 13:14 [PATCH v6 0/2] rcu/nocb: Delete local variable 'need_rcu_nocb_mask' in rcu_init_nohz() Zhen Lei
2022-09-01 13:14 ` [PATCH v6 1/2] rcu: Simplify rcu_init_nohz() cpumask handling Zhen Lei
@ 2022-09-01 13:14 ` Zhen Lei
1 sibling, 0 replies; 7+ messages in thread
From: Zhen Lei @ 2022-09-01 13:14 UTC (permalink / raw)
To: Paul E . McKenney, Frederic Weisbecker, Neeraj Upadhyay,
Josh Triplett, Steven Rostedt, Mathieu Desnoyers, Lai Jiangshan,
Joel Fernandes, rcu, linux-kernel
Cc: Zhen Lei
Offload callback processing from all CPUs as long as there is no
"rcu_nocbs=" boot parameter. This also means: whether
CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y takes effect does not depend on
the absence of "nohz_full=".
Suggested-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
---
kernel/rcu/Kconfig | 4 ++--
kernel/rcu/tree_nocb.h | 2 +-
2 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig
index d471d22a5e21b43..35b94f5f6767f00 100644
--- a/kernel/rcu/Kconfig
+++ b/kernel/rcu/Kconfig
@@ -270,8 +270,8 @@ config RCU_NOCB_CPU_DEFAULT_ALL
default n
help
Use this option to offload callback processing from all CPUs
- by default, in the absence of the rcu_nocbs or nohz_full boot
- parameter. This also avoids the need to use any boot parameters
+ by default, in the absence of the rcu_nocbs boot parameter.
+ This also avoids the need to use any boot parameters
to achieve the effect of offloading all CPUs on boot.
Say Y here if you want offload all CPUs by default on boot.
diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index 8b6dceeabde0b4d..cfbdd78d6c33158 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -1219,7 +1219,7 @@ void __init rcu_init_nohz(void)
#endif
#if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL)
- if (!rcu_state.nocb_is_setup && !cpumask)
+ if (!rcu_state.nocb_is_setup)
cpumask = cpu_possible_mask;
#endif
--
2.25.1
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH v6 1/2] rcu: Simplify rcu_init_nohz() cpumask handling
2022-09-01 13:14 ` [PATCH v6 1/2] rcu: Simplify rcu_init_nohz() cpumask handling Zhen Lei
@ 2022-09-01 13:25 ` Leizhen (ThunderTown)
2022-09-01 16:54 ` Paul E. McKenney
2022-09-07 11:04 ` Frederic Weisbecker
1 sibling, 1 reply; 7+ messages in thread
From: Leizhen (ThunderTown) @ 2022-09-01 13:25 UTC (permalink / raw)
To: Paul E . McKenney, Frederic Weisbecker, Neeraj Upadhyay,
Josh Triplett, Steven Rostedt, Mathieu Desnoyers, Lai Jiangshan,
Joel Fernandes, rcu, linux-kernel
On 2022/9/1 21:14, Zhen Lei wrote:
> In kernels built with either CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y or
> CONFIG_NO_HZ_FULL=y, additional CPUs must be added to rcu_nocb_mask.
> Except that kernels booted without the rcu_nocbs= will not have
> allocated rcu_nocb_mask. And the current rcu_init_nohz() function uses
> its need_rcu_nocb_mask and offload_all local variables to track the
> rcu_nocb and nohz_full state.
>
> But there is a much simpler approach, namely creating a cpumask pointer
> to track the default and then using cpumask_available() to check the
> rcu_nocb_mask state. This commit takes this approach, thereby simplifying
> and shortening the rcu_init_nohz() function.
>
> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Sorry, I forgot remove this "Signed-off-by".
> Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> ---
> kernel/rcu/tree_nocb.h | 35 ++++++++++++-----------------------
> 1 file changed, 12 insertions(+), 23 deletions(-)
>
> diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
> index 0a5f0ef41484518..8b6dceeabde0b4d 100644
> --- a/kernel/rcu/tree_nocb.h
> +++ b/kernel/rcu/tree_nocb.h
> @@ -1210,45 +1210,34 @@ EXPORT_SYMBOL_GPL(rcu_nocb_cpu_offload);
> void __init rcu_init_nohz(void)
> {
> int cpu;
> - bool need_rcu_nocb_mask = false;
> - bool offload_all = false;
> struct rcu_data *rdp;
> -
> -#if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL)
> - if (!rcu_state.nocb_is_setup) {
> - need_rcu_nocb_mask = true;
> - offload_all = true;
> - }
> -#endif /* #if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL) */
> + const struct cpumask *cpumask = NULL;
>
> #if defined(CONFIG_NO_HZ_FULL)
> - if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask)) {
> - need_rcu_nocb_mask = true;
> - offload_all = false; /* NO_HZ_FULL has its own mask. */
> - }
> -#endif /* #if defined(CONFIG_NO_HZ_FULL) */
> + if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask))
> + cpumask = tick_nohz_full_mask;
> +#endif
> +
> +#if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL)
> + if (!rcu_state.nocb_is_setup && !cpumask)
> + cpumask = cpu_possible_mask;
> +#endif
>
> - if (need_rcu_nocb_mask) {
> + if (cpumask) {
> if (!cpumask_available(rcu_nocb_mask)) {
> if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
> pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
> return;
> }
> }
> +
> + cpumask_or(rcu_nocb_mask, rcu_nocb_mask, cpumask);
> rcu_state.nocb_is_setup = true;
> }
>
> if (!rcu_state.nocb_is_setup)
> return;
>
> -#if defined(CONFIG_NO_HZ_FULL)
> - if (tick_nohz_full_running)
> - cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
> -#endif /* #if defined(CONFIG_NO_HZ_FULL) */
> -
> - if (offload_all)
> - cpumask_setall(rcu_nocb_mask);
> -
> if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
> pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n");
> cpumask_and(rcu_nocb_mask, cpu_possible_mask,
>
--
Regards,
Zhen Lei
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v6 1/2] rcu: Simplify rcu_init_nohz() cpumask handling
2022-09-01 13:25 ` Leizhen (ThunderTown)
@ 2022-09-01 16:54 ` Paul E. McKenney
0 siblings, 0 replies; 7+ messages in thread
From: Paul E. McKenney @ 2022-09-01 16:54 UTC (permalink / raw)
To: Leizhen (ThunderTown)
Cc: Frederic Weisbecker, Neeraj Upadhyay, Josh Triplett,
Steven Rostedt, Mathieu Desnoyers, Lai Jiangshan, Joel Fernandes,
rcu, linux-kernel
On Thu, Sep 01, 2022 at 09:25:06PM +0800, Leizhen (ThunderTown) wrote:
>
>
> On 2022/9/1 21:14, Zhen Lei wrote:
> > In kernels built with either CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y or
> > CONFIG_NO_HZ_FULL=y, additional CPUs must be added to rcu_nocb_mask.
> > Except that kernels booted without the rcu_nocbs= will not have
> > allocated rcu_nocb_mask. And the current rcu_init_nohz() function uses
> > its need_rcu_nocb_mask and offload_all local variables to track the
> > rcu_nocb and nohz_full state.
> >
> > But there is a much simpler approach, namely creating a cpumask pointer
> > to track the default and then using cpumask_available() to check the
> > rcu_nocb_mask state. This commit takes this approach, thereby simplifying
> > and shortening the rcu_init_nohz() function.
> >
> > Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
> > Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
>
> Sorry, I forgot remove this "Signed-off-by".
Not a problem, especially given that in view of my oversight on the
previous version, I am going to let Frederic take first crack at this
version. ;-)
Thanx, Paul
> > Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> > ---
> > kernel/rcu/tree_nocb.h | 35 ++++++++++++-----------------------
> > 1 file changed, 12 insertions(+), 23 deletions(-)
> >
> > diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
> > index 0a5f0ef41484518..8b6dceeabde0b4d 100644
> > --- a/kernel/rcu/tree_nocb.h
> > +++ b/kernel/rcu/tree_nocb.h
> > @@ -1210,45 +1210,34 @@ EXPORT_SYMBOL_GPL(rcu_nocb_cpu_offload);
> > void __init rcu_init_nohz(void)
> > {
> > int cpu;
> > - bool need_rcu_nocb_mask = false;
> > - bool offload_all = false;
> > struct rcu_data *rdp;
> > -
> > -#if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL)
> > - if (!rcu_state.nocb_is_setup) {
> > - need_rcu_nocb_mask = true;
> > - offload_all = true;
> > - }
> > -#endif /* #if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL) */
> > + const struct cpumask *cpumask = NULL;
> >
> > #if defined(CONFIG_NO_HZ_FULL)
> > - if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask)) {
> > - need_rcu_nocb_mask = true;
> > - offload_all = false; /* NO_HZ_FULL has its own mask. */
> > - }
> > -#endif /* #if defined(CONFIG_NO_HZ_FULL) */
> > + if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask))
> > + cpumask = tick_nohz_full_mask;
> > +#endif
> > +
> > +#if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL)
> > + if (!rcu_state.nocb_is_setup && !cpumask)
> > + cpumask = cpu_possible_mask;
> > +#endif
> >
> > - if (need_rcu_nocb_mask) {
> > + if (cpumask) {
> > if (!cpumask_available(rcu_nocb_mask)) {
> > if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
> > pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
> > return;
> > }
> > }
> > +
> > + cpumask_or(rcu_nocb_mask, rcu_nocb_mask, cpumask);
> > rcu_state.nocb_is_setup = true;
> > }
> >
> > if (!rcu_state.nocb_is_setup)
> > return;
> >
> > -#if defined(CONFIG_NO_HZ_FULL)
> > - if (tick_nohz_full_running)
> > - cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
> > -#endif /* #if defined(CONFIG_NO_HZ_FULL) */
> > -
> > - if (offload_all)
> > - cpumask_setall(rcu_nocb_mask);
> > -
> > if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
> > pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n");
> > cpumask_and(rcu_nocb_mask, cpu_possible_mask,
> >
>
> --
> Regards,
> Zhen Lei
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v6 1/2] rcu: Simplify rcu_init_nohz() cpumask handling
2022-09-01 13:14 ` [PATCH v6 1/2] rcu: Simplify rcu_init_nohz() cpumask handling Zhen Lei
2022-09-01 13:25 ` Leizhen (ThunderTown)
@ 2022-09-07 11:04 ` Frederic Weisbecker
2022-09-13 1:46 ` Leizhen (ThunderTown)
1 sibling, 1 reply; 7+ messages in thread
From: Frederic Weisbecker @ 2022-09-07 11:04 UTC (permalink / raw)
To: Zhen Lei
Cc: Paul E . McKenney, Neeraj Upadhyay, Josh Triplett,
Steven Rostedt, Mathieu Desnoyers, Lai Jiangshan, Joel Fernandes,
rcu, linux-kernel
On Thu, Sep 01, 2022 at 09:14:35PM +0800, Zhen Lei wrote:
> In kernels built with either CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y or
> CONFIG_NO_HZ_FULL=y, additional CPUs must be added to rcu_nocb_mask.
> Except that kernels booted without the rcu_nocbs= will not have
> allocated rcu_nocb_mask. And the current rcu_init_nohz() function uses
> its need_rcu_nocb_mask and offload_all local variables to track the
> rcu_nocb and nohz_full state.
>
> But there is a much simpler approach, namely creating a cpumask pointer
> to track the default and then using cpumask_available() to check the
> rcu_nocb_mask state. This commit takes this approach, thereby simplifying
> and shortening the rcu_init_nohz() function.
>
> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> ---
> kernel/rcu/tree_nocb.h | 35 ++++++++++++-----------------------
> 1 file changed, 12 insertions(+), 23 deletions(-)
>
> diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
> index 0a5f0ef41484518..8b6dceeabde0b4d 100644
> --- a/kernel/rcu/tree_nocb.h
> +++ b/kernel/rcu/tree_nocb.h
> @@ -1210,45 +1210,34 @@ EXPORT_SYMBOL_GPL(rcu_nocb_cpu_offload);
> void __init rcu_init_nohz(void)
> {
> int cpu;
> - bool need_rcu_nocb_mask = false;
> - bool offload_all = false;
> struct rcu_data *rdp;
> -
> -#if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL)
> - if (!rcu_state.nocb_is_setup) {
> - need_rcu_nocb_mask = true;
> - offload_all = true;
> - }
> -#endif /* #if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL) */
> + const struct cpumask *cpumask = NULL;
>
> #if defined(CONFIG_NO_HZ_FULL)
> - if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask)) {
> - need_rcu_nocb_mask = true;
> - offload_all = false; /* NO_HZ_FULL has its own mask. */
> - }
> -#endif /* #if defined(CONFIG_NO_HZ_FULL) */
> + if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask))
> + cpumask = tick_nohz_full_mask;
> +#endif
> +
> +#if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL)
> + if (!rcu_state.nocb_is_setup && !cpumask)
> + cpumask = cpu_possible_mask;
> +#endif
Good, and it can even use a simple condition:
if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL) &&
!rcu_state.nocb_is_setup && !cpumask)
cpumask = cpu_possible_mask;
Acked-by: Frederic Weisbecker <frederic@kernel.org>
>
> - if (need_rcu_nocb_mask) {
> + if (cpumask) {
> if (!cpumask_available(rcu_nocb_mask)) {
> if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
> pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
> return;
> }
> }
> +
> + cpumask_or(rcu_nocb_mask, rcu_nocb_mask, cpumask);
> rcu_state.nocb_is_setup = true;
> }
>
> if (!rcu_state.nocb_is_setup)
> return;
>
> -#if defined(CONFIG_NO_HZ_FULL)
> - if (tick_nohz_full_running)
> - cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
> -#endif /* #if defined(CONFIG_NO_HZ_FULL) */
> -
> - if (offload_all)
> - cpumask_setall(rcu_nocb_mask);
> -
> if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
> pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n");
> cpumask_and(rcu_nocb_mask, cpu_possible_mask,
> --
> 2.25.1
>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v6 1/2] rcu: Simplify rcu_init_nohz() cpumask handling
2022-09-07 11:04 ` Frederic Weisbecker
@ 2022-09-13 1:46 ` Leizhen (ThunderTown)
0 siblings, 0 replies; 7+ messages in thread
From: Leizhen (ThunderTown) @ 2022-09-13 1:46 UTC (permalink / raw)
To: Frederic Weisbecker
Cc: Paul E . McKenney, Neeraj Upadhyay, Josh Triplett,
Steven Rostedt, Mathieu Desnoyers, Lai Jiangshan, Joel Fernandes,
rcu, linux-kernel
On 2022/9/7 19:04, Frederic Weisbecker wrote:
> On Thu, Sep 01, 2022 at 09:14:35PM +0800, Zhen Lei wrote:
>> In kernels built with either CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y or
>> CONFIG_NO_HZ_FULL=y, additional CPUs must be added to rcu_nocb_mask.
>> Except that kernels booted without the rcu_nocbs= will not have
>> allocated rcu_nocb_mask. And the current rcu_init_nohz() function uses
>> its need_rcu_nocb_mask and offload_all local variables to track the
>> rcu_nocb and nohz_full state.
>>
>> But there is a much simpler approach, namely creating a cpumask pointer
>> to track the default and then using cpumask_available() to check the
>> rcu_nocb_mask state. This commit takes this approach, thereby simplifying
>> and shortening the rcu_init_nohz() function.
>>
>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
>> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
>> Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
>> ---
>> kernel/rcu/tree_nocb.h | 35 ++++++++++++-----------------------
>> 1 file changed, 12 insertions(+), 23 deletions(-)
>>
>> diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
>> index 0a5f0ef41484518..8b6dceeabde0b4d 100644
>> --- a/kernel/rcu/tree_nocb.h
>> +++ b/kernel/rcu/tree_nocb.h
>> @@ -1210,45 +1210,34 @@ EXPORT_SYMBOL_GPL(rcu_nocb_cpu_offload);
>> void __init rcu_init_nohz(void)
>> {
>> int cpu;
>> - bool need_rcu_nocb_mask = false;
>> - bool offload_all = false;
>> struct rcu_data *rdp;
>> -
>> -#if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL)
>> - if (!rcu_state.nocb_is_setup) {
>> - need_rcu_nocb_mask = true;
>> - offload_all = true;
>> - }
>> -#endif /* #if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL) */
>> + const struct cpumask *cpumask = NULL;
>>
>> #if defined(CONFIG_NO_HZ_FULL)
>> - if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask)) {
>> - need_rcu_nocb_mask = true;
>> - offload_all = false; /* NO_HZ_FULL has its own mask. */
>> - }
>> -#endif /* #if defined(CONFIG_NO_HZ_FULL) */
>> + if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask))
>> + cpumask = tick_nohz_full_mask;
>> +#endif
>> +
>> +#if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL)
>> + if (!rcu_state.nocb_is_setup && !cpumask)
>> + cpumask = cpu_possible_mask;
>> +#endif
>
> Good, and it can even use a simple condition:
>
> if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL) &&
> !rcu_state.nocb_is_setup && !cpumask)
> cpumask = cpu_possible_mask;
Okay, I'll revise it in v7.
>
>
> Acked-by: Frederic Weisbecker <frederic@kernel.org>
>
>
>>
>> - if (need_rcu_nocb_mask) {
>> + if (cpumask) {
>> if (!cpumask_available(rcu_nocb_mask)) {
>> if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
>> pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
>> return;
>> }
>> }
>> +
>> + cpumask_or(rcu_nocb_mask, rcu_nocb_mask, cpumask);
>> rcu_state.nocb_is_setup = true;
>> }
>>
>> if (!rcu_state.nocb_is_setup)
>> return;
>>
>> -#if defined(CONFIG_NO_HZ_FULL)
>> - if (tick_nohz_full_running)
>> - cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
>> -#endif /* #if defined(CONFIG_NO_HZ_FULL) */
>> -
>> - if (offload_all)
>> - cpumask_setall(rcu_nocb_mask);
>> -
>> if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
>> pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n");
>> cpumask_and(rcu_nocb_mask, cpu_possible_mask,
>> --
>> 2.25.1
>>
> .
>
--
Regards,
Zhen Lei
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2022-09-13 1:47 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-09-01 13:14 [PATCH v6 0/2] rcu/nocb: Delete local variable 'need_rcu_nocb_mask' in rcu_init_nohz() Zhen Lei
2022-09-01 13:14 ` [PATCH v6 1/2] rcu: Simplify rcu_init_nohz() cpumask handling Zhen Lei
2022-09-01 13:25 ` Leizhen (ThunderTown)
2022-09-01 16:54 ` Paul E. McKenney
2022-09-07 11:04 ` Frederic Weisbecker
2022-09-13 1:46 ` Leizhen (ThunderTown)
2022-09-01 13:14 ` [PATCH v6 2/2] rcu: Offload callback processing from all CPUs in the absence of rcu_nocbs= Zhen Lei
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