* [PATCH rcu 0/7] Callback-offload (nocb) updates for v6.1
@ 2022-08-31 18:10 Paul E. McKenney
2022-08-31 18:10 ` [PATCH rcu 1/3] rcu/nocb: Choose the right rcuog/rcuop kthreads to output Paul E. McKenney
` (2 more replies)
0 siblings, 3 replies; 9+ messages in thread
From: Paul E. McKenney @ 2022-08-31 18:10 UTC (permalink / raw)
To: rcu; +Cc: linux-kernel, kernel-team, rostedt
Hello!
This series provides NOCB-CPU updates:
1. Choose the right rcuog/rcuop kthreads to output, courtesy
of Zqiang.
2. Add CPU number to CPU-{,de}offload failure messages.
3. Simplify rcu_init_nohz() cpumask handling, courtesy of Zhen Lei.
Thanx, Paul
------------------------------------------------------------------------
b/kernel/rcu/tree_nocb.h | 6 +++---
kernel/rcu/tree_nocb.h | 36 +++++++++++-------------------------
2 files changed, 14 insertions(+), 28 deletions(-)
^ permalink raw reply [flat|nested] 9+ messages in thread
* [PATCH rcu 1/3] rcu/nocb: Choose the right rcuog/rcuop kthreads to output
2022-08-31 18:10 [PATCH rcu 0/7] Callback-offload (nocb) updates for v6.1 Paul E. McKenney
@ 2022-08-31 18:10 ` Paul E. McKenney
2022-08-31 18:10 ` [PATCH rcu 2/3] rcu/nocb: Add CPU number to CPU-{,de}offload failure messages Paul E. McKenney
2022-08-31 18:10 ` [PATCH rcu 3/3] rcu: Simplify rcu_init_nohz() cpumask handling Paul E. McKenney
2 siblings, 0 replies; 9+ messages in thread
From: Paul E. McKenney @ 2022-08-31 18:10 UTC (permalink / raw)
To: rcu; +Cc: linux-kernel, kernel-team, rostedt, Zqiang, Paul E . McKenney
From: Zqiang <qiang1.zhang@intel.com>
The show_rcu_nocb_gp_state() function is supposed to dump out the rcuog
kthread and the show_rcu_nocb_state() function is supposed to dump out
the rcuo[ps] kthread. Currently, both do a mixture, which is not optimal
for debugging, even though it does not affect functionality.
This commit therefore adjusts these two functions to focus on their
respective kthreads.
Signed-off-by: Zqiang <qiang1.zhang@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/tree_nocb.h | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index a8f574d8850d2..f20aec4f4394b 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -1452,8 +1452,8 @@ static void show_rcu_nocb_gp_state(struct rcu_data *rdp)
(long)rdp->nocb_gp_seq,
rnp->grplo, rnp->grphi, READ_ONCE(rdp->nocb_gp_loops),
rdp->nocb_gp_kthread ? task_state_to_char(rdp->nocb_gp_kthread) : '.',
- rdp->nocb_cb_kthread ? (int)task_cpu(rdp->nocb_gp_kthread) : -1,
- show_rcu_should_be_on_cpu(rdp->nocb_cb_kthread));
+ rdp->nocb_gp_kthread ? (int)task_cpu(rdp->nocb_gp_kthread) : -1,
+ show_rcu_should_be_on_cpu(rdp->nocb_gp_kthread));
}
/* Dump out nocb kthread state for the specified rcu_data structure. */
@@ -1497,7 +1497,7 @@ static void show_rcu_nocb_state(struct rcu_data *rdp)
".B"[!!rcu_cblist_n_cbs(&rdp->nocb_bypass)],
rcu_segcblist_n_cbs(&rdp->cblist),
rdp->nocb_cb_kthread ? task_state_to_char(rdp->nocb_cb_kthread) : '.',
- rdp->nocb_cb_kthread ? (int)task_cpu(rdp->nocb_gp_kthread) : -1,
+ rdp->nocb_cb_kthread ? (int)task_cpu(rdp->nocb_cb_kthread) : -1,
show_rcu_should_be_on_cpu(rdp->nocb_cb_kthread));
/* It is OK for GP kthreads to have GP state. */
--
2.31.1.189.g2e36527f23
^ permalink raw reply related [flat|nested] 9+ messages in thread
* [PATCH rcu 2/3] rcu/nocb: Add CPU number to CPU-{,de}offload failure messages
2022-08-31 18:10 [PATCH rcu 0/7] Callback-offload (nocb) updates for v6.1 Paul E. McKenney
2022-08-31 18:10 ` [PATCH rcu 1/3] rcu/nocb: Choose the right rcuog/rcuop kthreads to output Paul E. McKenney
@ 2022-08-31 18:10 ` Paul E. McKenney
2022-08-31 18:10 ` [PATCH rcu 3/3] rcu: Simplify rcu_init_nohz() cpumask handling Paul E. McKenney
2 siblings, 0 replies; 9+ messages in thread
From: Paul E. McKenney @ 2022-08-31 18:10 UTC (permalink / raw)
To: rcu
Cc: linux-kernel, kernel-team, rostedt, Paul E. McKenney,
Frederic Weisbecker
Offline CPUs cannot be offloaded or deoffloaded. Any attempt to offload
or deoffload an offline CPU causes a message to be printed on the console,
which is good, but this message does not contain the CPU number, which
is bad. Such a CPU number can be helpful when debugging, as it gives a
clear indication that the CPU in question is in fact offline. This commit
therefore adds the CPU number to the CPU-{,de}offload failure messages.
Cc: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/tree_nocb.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index f20aec4f4394b..0a5f0ef414845 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -1111,7 +1111,7 @@ int rcu_nocb_cpu_deoffload(int cpu)
if (!ret)
cpumask_clear_cpu(cpu, rcu_nocb_mask);
} else {
- pr_info("NOCB: Can't CB-deoffload an offline CPU\n");
+ pr_info("NOCB: Cannot CB-deoffload offline CPU %d\n", rdp->cpu);
ret = -EINVAL;
}
}
@@ -1196,7 +1196,7 @@ int rcu_nocb_cpu_offload(int cpu)
if (!ret)
cpumask_set_cpu(cpu, rcu_nocb_mask);
} else {
- pr_info("NOCB: Can't CB-offload an offline CPU\n");
+ pr_info("NOCB: Cannot CB-offload offline CPU %d\n", rdp->cpu);
ret = -EINVAL;
}
}
--
2.31.1.189.g2e36527f23
^ permalink raw reply related [flat|nested] 9+ messages in thread
* [PATCH rcu 3/3] rcu: Simplify rcu_init_nohz() cpumask handling
2022-08-31 18:10 [PATCH rcu 0/7] Callback-offload (nocb) updates for v6.1 Paul E. McKenney
2022-08-31 18:10 ` [PATCH rcu 1/3] rcu/nocb: Choose the right rcuog/rcuop kthreads to output Paul E. McKenney
2022-08-31 18:10 ` [PATCH rcu 2/3] rcu/nocb: Add CPU number to CPU-{,de}offload failure messages Paul E. McKenney
@ 2022-08-31 18:10 ` Paul E. McKenney
2022-09-01 9:15 ` Frederic Weisbecker
2 siblings, 1 reply; 9+ messages in thread
From: Paul E. McKenney @ 2022-08-31 18:10 UTC (permalink / raw)
To: rcu
Cc: linux-kernel, kernel-team, rostedt, Zhen Lei, Paul E . McKenney,
Joel Fernandes
From: Zhen Lei <thunder.leizhen@huawei.com>
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 | 32 +++++++++-----------------------
1 file changed, 9 insertions(+), 23 deletions(-)
diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index 0a5f0ef414845..c8167be2288fa 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -1210,45 +1210,31 @@ 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;
+ const struct cpumask *cpumask = NULL;
#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) */
+ cpumask = cpu_possible_mask;
+#elif defined(CONFIG_NO_HZ_FULL)
+ if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask))
+ cpumask = tick_nohz_full_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,
--
2.31.1.189.g2e36527f23
^ permalink raw reply related [flat|nested] 9+ messages in thread
* Re: [PATCH rcu 3/3] rcu: Simplify rcu_init_nohz() cpumask handling
2022-08-31 18:10 ` [PATCH rcu 3/3] rcu: Simplify rcu_init_nohz() cpumask handling Paul E. McKenney
@ 2022-09-01 9:15 ` Frederic Weisbecker
2022-09-01 10:25 ` Paul E. McKenney
0 siblings, 1 reply; 9+ messages in thread
From: Frederic Weisbecker @ 2022-09-01 9:15 UTC (permalink / raw)
To: Paul E. McKenney
Cc: rcu, linux-kernel, kernel-team, rostedt, Zhen Lei, Joel Fernandes
On Wed, Aug 31, 2022 at 11:10:44AM -0700, Paul E. McKenney wrote:
> From: Zhen Lei <thunder.leizhen@huawei.com>
>
> 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 | 32 +++++++++-----------------------
> 1 file changed, 9 insertions(+), 23 deletions(-)
>
> diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
> index 0a5f0ef414845..c8167be2288fa 100644
> --- a/kernel/rcu/tree_nocb.h
> +++ b/kernel/rcu/tree_nocb.h
> @@ -1210,45 +1210,31 @@ 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;
> + const struct cpumask *cpumask = NULL;
>
> #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) */
> + cpumask = cpu_possible_mask;
You're missing the rcu_state.nocb_is_setup check, so
CONFIG_RCU_NOCB_CPU_DEFAULT_ALL will now always override the rcu_nocbs=
parameter (should be the other way around).
> +#elif defined(CONFIG_NO_HZ_FULL)
> + if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask))
> + cpumask = tick_nohz_full_mask;
> +#endif
A subtle behaviour difference here too: CONFIG_RCU_NOCB_CPU_DEFAULT_ALL will
now override nohz_full=
I don't mind, it's probably what we want in the end, but the changelog should
tell about it, or even better, this should be a separate change.
Thanks.
>
> - 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,
> --
> 2.31.1.189.g2e36527f23
>
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH rcu 3/3] rcu: Simplify rcu_init_nohz() cpumask handling
2022-09-01 9:15 ` Frederic Weisbecker
@ 2022-09-01 10:25 ` Paul E. McKenney
2022-09-01 11:11 ` Frederic Weisbecker
0 siblings, 1 reply; 9+ messages in thread
From: Paul E. McKenney @ 2022-09-01 10:25 UTC (permalink / raw)
To: Frederic Weisbecker
Cc: rcu, linux-kernel, kernel-team, rostedt, Zhen Lei, Joel Fernandes
On Thu, Sep 01, 2022 at 11:15:57AM +0200, Frederic Weisbecker wrote:
> On Wed, Aug 31, 2022 at 11:10:44AM -0700, Paul E. McKenney wrote:
> > From: Zhen Lei <thunder.leizhen@huawei.com>
> >
> > 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 | 32 +++++++++-----------------------
> > 1 file changed, 9 insertions(+), 23 deletions(-)
> >
> > diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
> > index 0a5f0ef414845..c8167be2288fa 100644
> > --- a/kernel/rcu/tree_nocb.h
> > +++ b/kernel/rcu/tree_nocb.h
> > @@ -1210,45 +1210,31 @@ 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;
> > + const struct cpumask *cpumask = NULL;
> >
> > #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) */
> > + cpumask = cpu_possible_mask;
>
> You're missing the rcu_state.nocb_is_setup check, so
> CONFIG_RCU_NOCB_CPU_DEFAULT_ALL will now always override the rcu_nocbs=
> parameter (should be the other way around).
This is indeed a problem, so especially thank you for looking this over!
I will revert this patch.
> > +#elif defined(CONFIG_NO_HZ_FULL)
> > + if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask))
> > + cpumask = tick_nohz_full_mask;
> > +#endif
>
> A subtle behaviour difference here too: CONFIG_RCU_NOCB_CPU_DEFAULT_ALL will
> now override nohz_full=
>
> I don't mind, it's probably what we want in the end, but the changelog should
> tell about it, or even better, this should be a separate change.
Good point. Perhaps the key point is that if there is nohz_full=,
rcu_nocbs=, and CONFIG_RCU_NOCB_CPU_DEFAULT_ALL, we still need rcu_nocbs=
to include at least those bits set by nohz_full=.
Are there any other constraints?
Zhen Lei, please feel free to submit an updated patch.
Thanx, Paul
> Thanks.
>
> >
> > - 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,
> > --
> > 2.31.1.189.g2e36527f23
> >
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH rcu 3/3] rcu: Simplify rcu_init_nohz() cpumask handling
2022-09-01 10:25 ` Paul E. McKenney
@ 2022-09-01 11:11 ` Frederic Weisbecker
2022-09-01 11:36 ` Leizhen (ThunderTown)
2022-09-01 13:31 ` Paul E. McKenney
0 siblings, 2 replies; 9+ messages in thread
From: Frederic Weisbecker @ 2022-09-01 11:11 UTC (permalink / raw)
To: Paul E. McKenney
Cc: rcu, linux-kernel, kernel-team, rostedt, Zhen Lei, Joel Fernandes
On Thu, Sep 01, 2022 at 03:25:20AM -0700, Paul E. McKenney wrote:
> On Thu, Sep 01, 2022 at 11:15:57AM +0200, Frederic Weisbecker wrote:
> > > +#elif defined(CONFIG_NO_HZ_FULL)
> > > + if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask))
> > > + cpumask = tick_nohz_full_mask;
> > > +#endif
> >
> > A subtle behaviour difference here too: CONFIG_RCU_NOCB_CPU_DEFAULT_ALL will
> > now override nohz_full=
> >
> > I don't mind, it's probably what we want in the end, but the changelog should
> > tell about it, or even better, this should be a separate change.
>
> Good point. Perhaps the key point is that if there is nohz_full=,
> rcu_nocbs=, and CONFIG_RCU_NOCB_CPU_DEFAULT_ALL, we still need rcu_nocbs=
> to include at least those bits set by nohz_full=.
Not sure I get what you mean. nohz_full= should in any case always force
rcu_nocbs at least on the nohz_full CPUs.
For example assuming the following combination: rcu_nocbs=6, nohz_full=7 AND
CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y, then the result should be:
NOCB CPUs = 6,7
NOHZ_FULL CPUs = 7
(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y is overriden by rcu_nocbs=6).
Now if we have nohz_full=7 AND CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y, then the
result is expected to be either:
NOCB CPUs = 7 (upstream behaviour)
NOHZ_FULL CPUs = 7
or
NOCB CPUs = all
NOHZ_FULL CPUs = 7
The second makes more sense IMHO but that should be in a separate change.
Thanks.
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH rcu 3/3] rcu: Simplify rcu_init_nohz() cpumask handling
2022-09-01 11:11 ` Frederic Weisbecker
@ 2022-09-01 11:36 ` Leizhen (ThunderTown)
2022-09-01 13:31 ` Paul E. McKenney
1 sibling, 0 replies; 9+ messages in thread
From: Leizhen (ThunderTown) @ 2022-09-01 11:36 UTC (permalink / raw)
To: Frederic Weisbecker, Paul E. McKenney
Cc: rcu, linux-kernel, kernel-team, rostedt, Joel Fernandes
On 2022/9/1 19:11, Frederic Weisbecker wrote:
> On Thu, Sep 01, 2022 at 03:25:20AM -0700, Paul E. McKenney wrote:
>> On Thu, Sep 01, 2022 at 11:15:57AM +0200, Frederic Weisbecker wrote:
>>>> +#elif defined(CONFIG_NO_HZ_FULL)
>>>> + if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask))
>>>> + cpumask = tick_nohz_full_mask;
>>>> +#endif
>>>
>>> A subtle behaviour difference here too: CONFIG_RCU_NOCB_CPU_DEFAULT_ALL will
>>> now override nohz_full=
>>>
>>> I don't mind, it's probably what we want in the end, but the changelog should
>>> tell about it, or even better, this should be a separate change.
>>
>> Good point. Perhaps the key point is that if there is nohz_full=,
>> rcu_nocbs=, and CONFIG_RCU_NOCB_CPU_DEFAULT_ALL, we still need rcu_nocbs=
>> to include at least those bits set by nohz_full=.
>
> Not sure I get what you mean. nohz_full= should in any case always force
> rcu_nocbs at least on the nohz_full CPUs.
>
> For example assuming the following combination: rcu_nocbs=6, nohz_full=7 AND
> CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y, then the result should be:
>
> NOCB CPUs = 6,7
> NOHZ_FULL CPUs = 7
>
> (CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y is overriden by rcu_nocbs=6).
>
> Now if we have nohz_full=7 AND CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y, then the
> result is expected to be either:
>
> NOCB CPUs = 7 (upstream behaviour)
> NOHZ_FULL CPUs = 7
OK, I got it. CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y takes effect only when there
are no 'rcu_nocbs=' and 'nohz_full='.
>
> or
>
> NOCB CPUs = all
> NOHZ_FULL CPUs = 7
>
> The second makes more sense IMHO but that should be in a separate change.
OK, in this case, CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y takes effect only when there
is no 'rcu_nocbs='.
>
> Thanks.
> .
>
--
Regards,
Zhen Lei
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH rcu 3/3] rcu: Simplify rcu_init_nohz() cpumask handling
2022-09-01 11:11 ` Frederic Weisbecker
2022-09-01 11:36 ` Leizhen (ThunderTown)
@ 2022-09-01 13:31 ` Paul E. McKenney
1 sibling, 0 replies; 9+ messages in thread
From: Paul E. McKenney @ 2022-09-01 13:31 UTC (permalink / raw)
To: Frederic Weisbecker
Cc: rcu, linux-kernel, kernel-team, rostedt, Zhen Lei, Joel Fernandes
On Thu, Sep 01, 2022 at 01:11:14PM +0200, Frederic Weisbecker wrote:
> On Thu, Sep 01, 2022 at 03:25:20AM -0700, Paul E. McKenney wrote:
> > On Thu, Sep 01, 2022 at 11:15:57AM +0200, Frederic Weisbecker wrote:
> > > > +#elif defined(CONFIG_NO_HZ_FULL)
> > > > + if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask))
> > > > + cpumask = tick_nohz_full_mask;
> > > > +#endif
> > >
> > > A subtle behaviour difference here too: CONFIG_RCU_NOCB_CPU_DEFAULT_ALL will
> > > now override nohz_full=
> > >
> > > I don't mind, it's probably what we want in the end, but the changelog should
> > > tell about it, or even better, this should be a separate change.
> >
> > Good point. Perhaps the key point is that if there is nohz_full=,
> > rcu_nocbs=, and CONFIG_RCU_NOCB_CPU_DEFAULT_ALL, we still need rcu_nocbs=
> > to include at least those bits set by nohz_full=.
>
> Not sure I get what you mean. nohz_full= should in any case always force
> rcu_nocbs at least on the nohz_full CPUs.
>
> For example assuming the following combination: rcu_nocbs=6, nohz_full=7 AND
> CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y, then the result should be:
>
> NOCB CPUs = 6,7
> NOHZ_FULL CPUs = 7
>
> (CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y is overriden by rcu_nocbs=6).
>
> Now if we have nohz_full=7 AND CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y, then the
> result is expected to be either:
>
> NOCB CPUs = 7 (upstream behaviour)
> NOHZ_FULL CPUs = 7
>
> or
>
> NOCB CPUs = all
> NOHZ_FULL CPUs = 7
>
> The second makes more sense IMHO but that should be in a separate change.
Your examples are consistent with what I was trying to say. ;-)
Thanx, Paul
^ permalink raw reply [flat|nested] 9+ messages in thread
end of thread, other threads:[~2022-09-01 13:34 UTC | newest]
Thread overview: 9+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-08-31 18:10 [PATCH rcu 0/7] Callback-offload (nocb) updates for v6.1 Paul E. McKenney
2022-08-31 18:10 ` [PATCH rcu 1/3] rcu/nocb: Choose the right rcuog/rcuop kthreads to output Paul E. McKenney
2022-08-31 18:10 ` [PATCH rcu 2/3] rcu/nocb: Add CPU number to CPU-{,de}offload failure messages Paul E. McKenney
2022-08-31 18:10 ` [PATCH rcu 3/3] rcu: Simplify rcu_init_nohz() cpumask handling Paul E. McKenney
2022-09-01 9:15 ` Frederic Weisbecker
2022-09-01 10:25 ` Paul E. McKenney
2022-09-01 11:11 ` Frederic Weisbecker
2022-09-01 11:36 ` Leizhen (ThunderTown)
2022-09-01 13:31 ` Paul E. McKenney
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