From: Joel Fernandes <[email protected]>
On systems with CONFIG_RCU_NOCB_CPU=y, there is no default mask provided
which ends up not offloading any CPU. This patch removes a dependency
from the bootloader having to know about RCU and about how to provide
the mask.
With the new option enabled, all CPUs will be offloaded on boot unless
rcu_nocbs= or rcu_nohz_full= kernel parameters provide a CPU list.
Signed-off-by: Joel Fernandes <[email protected]>
---
v4: Rebased on rcu/dev, fixed conflict with Frederick's patch changing
location of nocb_is_setup variable.
Documentation/admin-guide/kernel-parameters.txt | 6 ++++++
kernel/rcu/Kconfig | 13 +++++++++++++
kernel/rcu/tree_nocb.h | 13 +++++++++++++
3 files changed, 32 insertions(+)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 789ef586009b..1e82ecb7a649 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3572,6 +3572,9 @@
just as if they had also been called out in the
rcu_nocbs= boot parameter.
+ Note that this argument takes precedence over
+ the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
+
noiotrap [SH] Disables trapped I/O port accesses.
noirqdebug [X86-32] Disables the code which attempts to detect and
@@ -4475,6 +4478,9 @@
no-callback mode from boot but the mode may be
toggled at runtime via cpusets.
+ Note that this argument takes precedence over
+ the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
+
rcu_nocb_poll [KNL]
Rather than requiring that offloaded CPUs
(specified by rcu_nocbs= above) explicitly
diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig
index 1c630e573548..27aab870ae4c 100644
--- a/kernel/rcu/Kconfig
+++ b/kernel/rcu/Kconfig
@@ -262,6 +262,19 @@ config RCU_NOCB_CPU
Say Y here if you need reduced OS jitter, despite added overhead.
Say N here if you are unsure.
+config RCU_NOCB_CPU_DEFAULT_ALL
+ bool "Offload RCU callback processing from all CPUs by default"
+ depends on RCU_NOCB_CPU
+ 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
+ to achieve the effect of offloading all CPUs on boot.
+
+ Say Y here if you want offload all CPUs by default on boot.
+ Say N here if you are unsure.
+
config TASKS_TRACE_RCU_READ_MB
bool "Tasks Trace RCU readers use memory barriers in user and idle"
depends on RCU_EXPERT && TASKS_TRACE_RCU
diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index 4cf9a29bba79..9f29f25a0cbc 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -1197,11 +1197,21 @@ 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) */
+
#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 (need_rcu_nocb_mask) {
@@ -1222,6 +1232,9 @@ void __init rcu_init_nohz(void)
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,
--
2.36.0.rc0.470.gd361397f0d-goog
On Tue, Apr 19, 2022 at 04:10:33PM -0400, Joel Fernandes wrote:
> On Tue, Apr 19, 2022 at 4:08 PM Joel Fernandes (Google)
> <[email protected]> wrote:
> >
> > From: Joel Fernandes <[email protected]>
> >
> > On systems with CONFIG_RCU_NOCB_CPU=y, there is no default mask provided
> > which ends up not offloading any CPU. This patch removes a dependency
> > from the bootloader having to know about RCU and about how to provide
> > the mask.
> >
> > With the new option enabled, all CPUs will be offloaded on boot unless
> > rcu_nocbs= or rcu_nohz_full= kernel parameters provide a CPU list.
> >
> > Signed-off-by: Joel Fernandes <[email protected]>
>
> Oops, forgot to add Reviewed-by tags:
> Reviewed-by: Uladzislau Rezki (Sony) <[email protected]>
> Reviewed-by: Kalesh Singh <[email protected]>
>
> Paul, would you mind doing so, so I don't have to resend? Apologies.
OK, but only because it passed an allmodconfig build this time. ;-)
Thanx, Paul
> Thanks,
>
> Joel
>
>
> > ---
> > v4: Rebased on rcu/dev, fixed conflict with Frederick's patch changing
> > location of nocb_is_setup variable.
> >
> > Documentation/admin-guide/kernel-parameters.txt | 6 ++++++
> > kernel/rcu/Kconfig | 13 +++++++++++++
> > kernel/rcu/tree_nocb.h | 13 +++++++++++++
> > 3 files changed, 32 insertions(+)
> >
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index 789ef586009b..1e82ecb7a649 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -3572,6 +3572,9 @@
> > just as if they had also been called out in the
> > rcu_nocbs= boot parameter.
> >
> > + Note that this argument takes precedence over
> > + the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
> > +
> > noiotrap [SH] Disables trapped I/O port accesses.
> >
> > noirqdebug [X86-32] Disables the code which attempts to detect and
> > @@ -4475,6 +4478,9 @@
> > no-callback mode from boot but the mode may be
> > toggled at runtime via cpusets.
> >
> > + Note that this argument takes precedence over
> > + the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
> > +
> > rcu_nocb_poll [KNL]
> > Rather than requiring that offloaded CPUs
> > (specified by rcu_nocbs= above) explicitly
> > diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig
> > index 1c630e573548..27aab870ae4c 100644
> > --- a/kernel/rcu/Kconfig
> > +++ b/kernel/rcu/Kconfig
> > @@ -262,6 +262,19 @@ config RCU_NOCB_CPU
> > Say Y here if you need reduced OS jitter, despite added overhead.
> > Say N here if you are unsure.
> >
> > +config RCU_NOCB_CPU_DEFAULT_ALL
> > + bool "Offload RCU callback processing from all CPUs by default"
> > + depends on RCU_NOCB_CPU
> > + 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
> > + to achieve the effect of offloading all CPUs on boot.
> > +
> > + Say Y here if you want offload all CPUs by default on boot.
> > + Say N here if you are unsure.
> > +
> > config TASKS_TRACE_RCU_READ_MB
> > bool "Tasks Trace RCU readers use memory barriers in user and idle"
> > depends on RCU_EXPERT && TASKS_TRACE_RCU
> > diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
> > index 4cf9a29bba79..9f29f25a0cbc 100644
> > --- a/kernel/rcu/tree_nocb.h
> > +++ b/kernel/rcu/tree_nocb.h
> > @@ -1197,11 +1197,21 @@ 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) */
> > +
> > #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 (need_rcu_nocb_mask) {
> > @@ -1222,6 +1232,9 @@ void __init rcu_init_nohz(void)
> > 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,
> > --
> > 2.36.0.rc0.470.gd361397f0d-goog
> >
On Tue, Apr 19, 2022 at 4:08 PM Joel Fernandes (Google)
<[email protected]> wrote:
>
> From: Joel Fernandes <[email protected]>
>
> On systems with CONFIG_RCU_NOCB_CPU=y, there is no default mask provided
> which ends up not offloading any CPU. This patch removes a dependency
> from the bootloader having to know about RCU and about how to provide
> the mask.
>
> With the new option enabled, all CPUs will be offloaded on boot unless
> rcu_nocbs= or rcu_nohz_full= kernel parameters provide a CPU list.
>
> Signed-off-by: Joel Fernandes <[email protected]>
Oops, forgot to add Reviewed-by tags:
Reviewed-by: Uladzislau Rezki (Sony) <[email protected]>
Reviewed-by: Kalesh Singh <[email protected]>
Paul, would you mind doing so, so I don't have to resend? Apologies.
Thanks,
Joel
> ---
> v4: Rebased on rcu/dev, fixed conflict with Frederick's patch changing
> location of nocb_is_setup variable.
>
> Documentation/admin-guide/kernel-parameters.txt | 6 ++++++
> kernel/rcu/Kconfig | 13 +++++++++++++
> kernel/rcu/tree_nocb.h | 13 +++++++++++++
> 3 files changed, 32 insertions(+)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 789ef586009b..1e82ecb7a649 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -3572,6 +3572,9 @@
> just as if they had also been called out in the
> rcu_nocbs= boot parameter.
>
> + Note that this argument takes precedence over
> + the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
> +
> noiotrap [SH] Disables trapped I/O port accesses.
>
> noirqdebug [X86-32] Disables the code which attempts to detect and
> @@ -4475,6 +4478,9 @@
> no-callback mode from boot but the mode may be
> toggled at runtime via cpusets.
>
> + Note that this argument takes precedence over
> + the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
> +
> rcu_nocb_poll [KNL]
> Rather than requiring that offloaded CPUs
> (specified by rcu_nocbs= above) explicitly
> diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig
> index 1c630e573548..27aab870ae4c 100644
> --- a/kernel/rcu/Kconfig
> +++ b/kernel/rcu/Kconfig
> @@ -262,6 +262,19 @@ config RCU_NOCB_CPU
> Say Y here if you need reduced OS jitter, despite added overhead.
> Say N here if you are unsure.
>
> +config RCU_NOCB_CPU_DEFAULT_ALL
> + bool "Offload RCU callback processing from all CPUs by default"
> + depends on RCU_NOCB_CPU
> + 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
> + to achieve the effect of offloading all CPUs on boot.
> +
> + Say Y here if you want offload all CPUs by default on boot.
> + Say N here if you are unsure.
> +
> config TASKS_TRACE_RCU_READ_MB
> bool "Tasks Trace RCU readers use memory barriers in user and idle"
> depends on RCU_EXPERT && TASKS_TRACE_RCU
> diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
> index 4cf9a29bba79..9f29f25a0cbc 100644
> --- a/kernel/rcu/tree_nocb.h
> +++ b/kernel/rcu/tree_nocb.h
> @@ -1197,11 +1197,21 @@ 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) */
> +
> #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 (need_rcu_nocb_mask) {
> @@ -1222,6 +1232,9 @@ void __init rcu_init_nohz(void)
> 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,
> --
> 2.36.0.rc0.470.gd361397f0d-goog
>
On Tue, Apr 19, 2022 at 04:56:26PM -0700, Paul E. McKenney wrote:
> On Tue, Apr 19, 2022 at 04:10:33PM -0400, Joel Fernandes wrote:
> > On Tue, Apr 19, 2022 at 4:08 PM Joel Fernandes (Google)
> > <[email protected]> wrote:
> > >
> > > From: Joel Fernandes <[email protected]>
> > >
> > > On systems with CONFIG_RCU_NOCB_CPU=y, there is no default mask provided
> > > which ends up not offloading any CPU. This patch removes a dependency
> > > from the bootloader having to know about RCU and about how to provide
> > > the mask.
> > >
> > > With the new option enabled, all CPUs will be offloaded on boot unless
> > > rcu_nocbs= or rcu_nohz_full= kernel parameters provide a CPU list.
> > >
> > > Signed-off-by: Joel Fernandes <[email protected]>
> >
> > Oops, forgot to add Reviewed-by tags:
> > Reviewed-by: Uladzislau Rezki (Sony) <[email protected]>
> > Reviewed-by: Kalesh Singh <[email protected]>
> >
> > Paul, would you mind doing so, so I don't have to resend? Apologies.
>
> OK, but only because it passed an allmodconfig build this time. ;-)
But the rcutorture TASKS03 scenario failed to build. Kernel test robot
saw similar issues here:
https://lore.kernel.org/all/[email protected]/
Next version! ;-)
Thanx, Paul
> > Thanks,
> >
> > Joel
> >
> >
> > > ---
> > > v4: Rebased on rcu/dev, fixed conflict with Frederick's patch changing
> > > location of nocb_is_setup variable.
> > >
> > > Documentation/admin-guide/kernel-parameters.txt | 6 ++++++
> > > kernel/rcu/Kconfig | 13 +++++++++++++
> > > kernel/rcu/tree_nocb.h | 13 +++++++++++++
> > > 3 files changed, 32 insertions(+)
> > >
> > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > > index 789ef586009b..1e82ecb7a649 100644
> > > --- a/Documentation/admin-guide/kernel-parameters.txt
> > > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > > @@ -3572,6 +3572,9 @@
> > > just as if they had also been called out in the
> > > rcu_nocbs= boot parameter.
> > >
> > > + Note that this argument takes precedence over
> > > + the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
> > > +
> > > noiotrap [SH] Disables trapped I/O port accesses.
> > >
> > > noirqdebug [X86-32] Disables the code which attempts to detect and
> > > @@ -4475,6 +4478,9 @@
> > > no-callback mode from boot but the mode may be
> > > toggled at runtime via cpusets.
> > >
> > > + Note that this argument takes precedence over
> > > + the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
> > > +
> > > rcu_nocb_poll [KNL]
> > > Rather than requiring that offloaded CPUs
> > > (specified by rcu_nocbs= above) explicitly
> > > diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig
> > > index 1c630e573548..27aab870ae4c 100644
> > > --- a/kernel/rcu/Kconfig
> > > +++ b/kernel/rcu/Kconfig
> > > @@ -262,6 +262,19 @@ config RCU_NOCB_CPU
> > > Say Y here if you need reduced OS jitter, despite added overhead.
> > > Say N here if you are unsure.
> > >
> > > +config RCU_NOCB_CPU_DEFAULT_ALL
> > > + bool "Offload RCU callback processing from all CPUs by default"
> > > + depends on RCU_NOCB_CPU
> > > + 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
> > > + to achieve the effect of offloading all CPUs on boot.
> > > +
> > > + Say Y here if you want offload all CPUs by default on boot.
> > > + Say N here if you are unsure.
> > > +
> > > config TASKS_TRACE_RCU_READ_MB
> > > bool "Tasks Trace RCU readers use memory barriers in user and idle"
> > > depends on RCU_EXPERT && TASKS_TRACE_RCU
> > > diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
> > > index 4cf9a29bba79..9f29f25a0cbc 100644
> > > --- a/kernel/rcu/tree_nocb.h
> > > +++ b/kernel/rcu/tree_nocb.h
> > > @@ -1197,11 +1197,21 @@ 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) */
> > > +
> > > #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 (need_rcu_nocb_mask) {
> > > @@ -1222,6 +1232,9 @@ void __init rcu_init_nohz(void)
> > > 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,
> > > --
> > > 2.36.0.rc0.470.gd361397f0d-goog
> > >