Currently, If the 'rcu_nocb_poll' bootargs is enable, all rcuog kthreads
enter polling mode. however, due to only insert CPU's rdp which belong to
rcu_nocb_mask to 'nocb_head_rdp' list or all CPU's rdp served by rcuog
kthread have been de-offloaded, these cause the 'nocb_head_rdp' list
served by rcuog kthread is empty, when the 'nocb_head_rdp' is empty,
the rcuog kthread in polling mode not actually do anything. fix it by
exiting polling mode when the 'nocb_head_rdp'list is empty, otherwise
entering polling mode.
Signed-off-by: Zqiang <[email protected]>
---
v1->v2:
Move rcu_nocb_poll flags check from rdp_offload_toggle() to
rcu_nocb_rdp_offload/deoffload(), avoid unnecessary setting of
rdp_gp->nocb_gp_sleep flags, because when rcu_nocb_poll is set
the rdp_gp->nocb_gp_sleep is not used.
kernel/rcu/tree_nocb.h | 16 ++++++++++------
1 file changed, 10 insertions(+), 6 deletions(-)
diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index fa8e4f82e60c..2a52c9abc681 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -698,10 +698,14 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
TPS("WakeBypassIsDeferred"));
}
if (rcu_nocb_poll) {
- /* Polling, so trace if first poll in the series. */
- if (gotcbs)
- trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
- schedule_timeout_idle(1);
+ if (list_empty(&my_rdp->nocb_head_rdp)) {
+ rcu_wait(READ_ONCE(my_rdp->nocb_toggling_rdp));
+ } else {
+ /* Polling, so trace if first poll in the series. */
+ if (gotcbs)
+ trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
+ schedule_timeout_idle(1);
+ }
} else if (!needwait_gp) {
/* Wait for callbacks to appear. */
trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Sleep"));
@@ -1030,7 +1034,7 @@ static long rcu_nocb_rdp_deoffload(void *arg)
mutex_lock(&rdp_gp->nocb_gp_kthread_mutex);
if (rdp_gp->nocb_gp_kthread) {
- if (wake_gp)
+ if (wake_gp || rcu_nocb_poll)
wake_up_process(rdp_gp->nocb_gp_kthread);
/*
@@ -1152,7 +1156,7 @@ static long rcu_nocb_rdp_offload(void *arg)
* rcu_nocb_unlock() rcu_nocb_unlock()
*/
wake_gp = rdp_offload_toggle(rdp, true, flags);
- if (wake_gp)
+ if (wake_gp || rcu_nocb_poll)
wake_up_process(rdp_gp->nocb_gp_kthread);
swait_event_exclusive(rdp->nocb_state_wq,
rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB) &&
--
2.25.1
On Tue, Jun 07, 2022 at 03:50:57PM +0800, Zqiang wrote:
> Currently, If the 'rcu_nocb_poll' bootargs is enable, all rcuog kthreads
> enter polling mode. however, due to only insert CPU's rdp which belong to
> rcu_nocb_mask to 'nocb_head_rdp' list or all CPU's rdp served by rcuog
> kthread have been de-offloaded, these cause the 'nocb_head_rdp' list
> served by rcuog kthread is empty, when the 'nocb_head_rdp' is empty,
> the rcuog kthread in polling mode not actually do anything. fix it by
> exiting polling mode when the 'nocb_head_rdp'list is empty, otherwise
> entering polling mode.
>
> Signed-off-by: Zqiang <[email protected]>
This looks a bit more plausible, but what have you done to test this?
Thanx, Paul
> ---
> v1->v2:
> Move rcu_nocb_poll flags check from rdp_offload_toggle() to
> rcu_nocb_rdp_offload/deoffload(), avoid unnecessary setting of
> rdp_gp->nocb_gp_sleep flags, because when rcu_nocb_poll is set
> the rdp_gp->nocb_gp_sleep is not used.
>
> kernel/rcu/tree_nocb.h | 16 ++++++++++------
> 1 file changed, 10 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
> index fa8e4f82e60c..2a52c9abc681 100644
> --- a/kernel/rcu/tree_nocb.h
> +++ b/kernel/rcu/tree_nocb.h
> @@ -698,10 +698,14 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
> TPS("WakeBypassIsDeferred"));
> }
> if (rcu_nocb_poll) {
> - /* Polling, so trace if first poll in the series. */
> - if (gotcbs)
> - trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
> - schedule_timeout_idle(1);
> + if (list_empty(&my_rdp->nocb_head_rdp)) {
> + rcu_wait(READ_ONCE(my_rdp->nocb_toggling_rdp));
> + } else {
> + /* Polling, so trace if first poll in the series. */
> + if (gotcbs)
> + trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
> + schedule_timeout_idle(1);
> + }
> } else if (!needwait_gp) {
> /* Wait for callbacks to appear. */
> trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Sleep"));
> @@ -1030,7 +1034,7 @@ static long rcu_nocb_rdp_deoffload(void *arg)
>
> mutex_lock(&rdp_gp->nocb_gp_kthread_mutex);
> if (rdp_gp->nocb_gp_kthread) {
> - if (wake_gp)
> + if (wake_gp || rcu_nocb_poll)
> wake_up_process(rdp_gp->nocb_gp_kthread);
>
> /*
> @@ -1152,7 +1156,7 @@ static long rcu_nocb_rdp_offload(void *arg)
> * rcu_nocb_unlock() rcu_nocb_unlock()
> */
> wake_gp = rdp_offload_toggle(rdp, true, flags);
> - if (wake_gp)
> + if (wake_gp || rcu_nocb_poll)
> wake_up_process(rdp_gp->nocb_gp_kthread);
> swait_event_exclusive(rdp->nocb_state_wq,
> rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB) &&
> --
> 2.25.1
>
On Wed, Jun 08, 2022 at 12:41:28AM +0000, Zhang, Qiang1 wrote:
> On Tue, Jun 07, 2022 at 03:50:57PM +0800, Zqiang wrote:
> > Currently, If the 'rcu_nocb_poll' bootargs is enable, all rcuog
> > kthreads enter polling mode. however, due to only insert CPU's rdp
> > which belong to rcu_nocb_mask to 'nocb_head_rdp' list or all CPU's rdp
> > served by rcuog kthread have been de-offloaded, these cause the
> > 'nocb_head_rdp' list served by rcuog kthread is empty, when the
> > 'nocb_head_rdp' is empty, the rcuog kthread in polling mode not
> > actually do anything. fix it by exiting polling mode when the
> > 'nocb_head_rdp'list is empty, otherwise entering polling mode.
> >
> > Signed-off-by: Zqiang <[email protected]>
> >
> >This looks a bit more plausible, but what have you done to test this?
>
> Yes , I have only tested as follows and I added two trace events.
>
> + trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("EnterNoPoll"));
> rcu_wait(READ_ONCE(my_rdp->nocb_toggling_rdp));
> + trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("ExitNoPoll"));
>
> runqemu kvm slirp nographic qemuparams="-m 2048 -smp 4" bootparams="rcu_nocbs=2,3 rcutree.dump_tree=1 rcu_nocb_poll rcutorture.nocbs_nthreads=4 rcutorture.test_boost=0" -d
To exercise your change, could you please also add an appropriate value
for the rcutorture.nocbs_nthreads kernel boot parameter? Without that
boot parameter, your kernel will not actually offload or deoffload
any CPUs.
An alternative approach is to run rcutorture scenario TREE01.
Thanx, Paul
> Thanks
> Zqiang
>
> >
> > Thanx, Paul
> >
> > ---
> > v1->v2:
> > Move rcu_nocb_poll flags check from rdp_offload_toggle() to
> > rcu_nocb_rdp_offload/deoffload(), avoid unnecessary setting of
> > rdp_gp->nocb_gp_sleep flags, because when rcu_nocb_poll is set the
> > rdp_gp->nocb_gp_sleep is not used.
> >
> > kernel/rcu/tree_nocb.h | 16 ++++++++++------
> > 1 file changed, 10 insertions(+), 6 deletions(-)
> >
> > diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index
> > fa8e4f82e60c..2a52c9abc681 100644
> > --- a/kernel/rcu/tree_nocb.h
> > +++ b/kernel/rcu/tree_nocb.h
> > @@ -698,10 +698,14 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
> > TPS("WakeBypassIsDeferred"));
> > }
> > if (rcu_nocb_poll) {
> > - /* Polling, so trace if first poll in the series. */
> > - if (gotcbs)
> > - trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
> > - schedule_timeout_idle(1);
> > + if (list_empty(&my_rdp->nocb_head_rdp)) {
> > + rcu_wait(READ_ONCE(my_rdp->nocb_toggling_rdp));
> > + } else {
> > + /* Polling, so trace if first poll in the series. */
> > + if (gotcbs)
> > + trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
> > + schedule_timeout_idle(1);
> > + }
> > } else if (!needwait_gp) {
> > /* Wait for callbacks to appear. */
> > trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Sleep")); @@ -1030,7
> > +1034,7 @@ static long rcu_nocb_rdp_deoffload(void *arg)
> >
> > mutex_lock(&rdp_gp->nocb_gp_kthread_mutex);
> > if (rdp_gp->nocb_gp_kthread) {
> > - if (wake_gp)
> > + if (wake_gp || rcu_nocb_poll)
> > wake_up_process(rdp_gp->nocb_gp_kthread);
> >
> > /*
> > @@ -1152,7 +1156,7 @@ static long rcu_nocb_rdp_offload(void *arg)
> > * rcu_nocb_unlock() rcu_nocb_unlock()
> > */
> > wake_gp = rdp_offload_toggle(rdp, true, flags);
> > - if (wake_gp)
> > + if (wake_gp || rcu_nocb_poll)
> > wake_up_process(rdp_gp->nocb_gp_kthread);
> > swait_event_exclusive(rdp->nocb_state_wq,
> > rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB) &&
> > --
> > 2.25.1
> >
On Tue, Jun 07, 2022 at 03:50:57PM +0800, Zqiang wrote:
> Currently, If the 'rcu_nocb_poll' bootargs is enable, all rcuog
> kthreads enter polling mode. however, due to only insert CPU's rdp
> which belong to rcu_nocb_mask to 'nocb_head_rdp' list or all CPU's rdp
> served by rcuog kthread have been de-offloaded, these cause the
> 'nocb_head_rdp' list served by rcuog kthread is empty, when the
> 'nocb_head_rdp' is empty, the rcuog kthread in polling mode not
> actually do anything. fix it by exiting polling mode when the
> 'nocb_head_rdp'list is empty, otherwise entering polling mode.
>
> Signed-off-by: Zqiang <[email protected]>
>
>This looks a bit more plausible, but what have you done to test this?
Yes , I have only tested as follows and I added two trace events.
+ trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("EnterNoPoll"));
rcu_wait(READ_ONCE(my_rdp->nocb_toggling_rdp));
+ trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("ExitNoPoll"));
runqemu kvm slirp nographic qemuparams="-m 2048 -smp 4" bootparams="rcu_nocbs=2,3 rcutree.dump_tree=1 rcu_nocb_poll rcutorture.nocbs_nthreads=4 rcutorture.test_boost=0" -d
Thanks
Zqiang
>
> Thanx, Paul
>
> ---
> v1->v2:
> Move rcu_nocb_poll flags check from rdp_offload_toggle() to
> rcu_nocb_rdp_offload/deoffload(), avoid unnecessary setting of
> rdp_gp->nocb_gp_sleep flags, because when rcu_nocb_poll is set the
> rdp_gp->nocb_gp_sleep is not used.
>
> kernel/rcu/tree_nocb.h | 16 ++++++++++------
> 1 file changed, 10 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index
> fa8e4f82e60c..2a52c9abc681 100644
> --- a/kernel/rcu/tree_nocb.h
> +++ b/kernel/rcu/tree_nocb.h
> @@ -698,10 +698,14 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
> TPS("WakeBypassIsDeferred"));
> }
> if (rcu_nocb_poll) {
> - /* Polling, so trace if first poll in the series. */
> - if (gotcbs)
> - trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
> - schedule_timeout_idle(1);
> + if (list_empty(&my_rdp->nocb_head_rdp)) {
> + rcu_wait(READ_ONCE(my_rdp->nocb_toggling_rdp));
> + } else {
> + /* Polling, so trace if first poll in the series. */
> + if (gotcbs)
> + trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
> + schedule_timeout_idle(1);
> + }
> } else if (!needwait_gp) {
> /* Wait for callbacks to appear. */
> trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Sleep")); @@ -1030,7
> +1034,7 @@ static long rcu_nocb_rdp_deoffload(void *arg)
>
> mutex_lock(&rdp_gp->nocb_gp_kthread_mutex);
> if (rdp_gp->nocb_gp_kthread) {
> - if (wake_gp)
> + if (wake_gp || rcu_nocb_poll)
> wake_up_process(rdp_gp->nocb_gp_kthread);
>
> /*
> @@ -1152,7 +1156,7 @@ static long rcu_nocb_rdp_offload(void *arg)
> * rcu_nocb_unlock() rcu_nocb_unlock()
> */
> wake_gp = rdp_offload_toggle(rdp, true, flags);
> - if (wake_gp)
> + if (wake_gp || rcu_nocb_poll)
> wake_up_process(rdp_gp->nocb_gp_kthread);
> swait_event_exclusive(rdp->nocb_state_wq,
> rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB) &&
> --
> 2.25.1
>
On Wed, Jun 08, 2022 at 01:01:31AM +0000, Zhang, Qiang1 wrote:
> On Wed, Jun 08, 2022 at 12:41:28AM +0000, Zhang, Qiang1 wrote:
> > On Tue, Jun 07, 2022 at 03:50:57PM +0800, Zqiang wrote:
> > > Currently, If the 'rcu_nocb_poll' bootargs is enable, all rcuog
> > > kthreads enter polling mode. however, due to only insert CPU's rdp
> > > which belong to rcu_nocb_mask to 'nocb_head_rdp' list or all CPU's
> > > rdp served by rcuog kthread have been de-offloaded, these cause the
> > > 'nocb_head_rdp' list served by rcuog kthread is empty, when the
> > > 'nocb_head_rdp' is empty, the rcuog kthread in polling mode not
> > > actually do anything. fix it by exiting polling mode when the
> > > 'nocb_head_rdp'list is empty, otherwise entering polling mode.
> > >
> > > Signed-off-by: Zqiang <[email protected]>
> > >
> > >This looks a bit more plausible, but what have you done to test this?
> >
> > Yes , I have only tested as follows and I added two trace events.
> >
> > + trace_rcu_nocb_wake(rcu_state.name, cpu,
> > + TPS("EnterNoPoll"));
> >
> > rcu_wait(READ_ONCE(my_rdp->nocb_toggling_rdp));
> > + trace_rcu_nocb_wake(rcu_state.name, cpu,
> > + TPS("ExitNoPoll"));
> >
> > runqemu kvm slirp nographic qemuparams="-m 2048 -smp 4"
> > bootparams="rcu_nocbs=2,3 rcutree.dump_tree=1 rcu_nocb_poll
> > rcutorture.nocbs_nthreads=4 rcutorture.test_boost=0" -d
>
> >To exercise your change, could you please also add an appropriate value for the rcutorture.nocbs_nthreads kernel boot parameter? Without that boot parameter, your kernel will not actually offload or deoffload any CPUs.
>
> I have set ' rcutorture.nocbs_nthreads=4 ' in bootargs.
I see it now, apologies for my confusion!
Thanx, Paul
> >An alternative approach is to run rcutorture scenario TREE01.
>
> I will also use TREE01 for testing
>
> Thanks
> Zqiang
>
> >
> > Thanx, Paul
>
> > Thanks
> > Zqiang
> >
> > >
> > > Thanx, Paul
> > >
> > > ---
> > > v1->v2:
> > > Move rcu_nocb_poll flags check from rdp_offload_toggle() to
> > > rcu_nocb_rdp_offload/deoffload(), avoid unnecessary setting of
> > > rdp_gp->nocb_gp_sleep flags, because when rcu_nocb_poll is set the
> > > rdp_gp->nocb_gp_sleep is not used.
> > >
> > > kernel/rcu/tree_nocb.h | 16 ++++++++++------
> > > 1 file changed, 10 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index
> > > fa8e4f82e60c..2a52c9abc681 100644
> > > --- a/kernel/rcu/tree_nocb.h
> > > +++ b/kernel/rcu/tree_nocb.h
> > > @@ -698,10 +698,14 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
> > > TPS("WakeBypassIsDeferred"));
> > > }
> > > if (rcu_nocb_poll) {
> > > - /* Polling, so trace if first poll in the series. */
> > > - if (gotcbs)
> > > - trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
> > > - schedule_timeout_idle(1);
> > > + if (list_empty(&my_rdp->nocb_head_rdp)) {
> > > + rcu_wait(READ_ONCE(my_rdp->nocb_toggling_rdp));
> > > + } else {
> > > + /* Polling, so trace if first poll in the series. */
> > > + if (gotcbs)
> > > + trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
> > > + schedule_timeout_idle(1);
> > > + }
> > > } else if (!needwait_gp) {
> > > /* Wait for callbacks to appear. */
> > > trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Sleep")); @@
> > > -1030,7
> > > +1034,7 @@ static long rcu_nocb_rdp_deoffload(void *arg)
> > >
> > > mutex_lock(&rdp_gp->nocb_gp_kthread_mutex);
> > > if (rdp_gp->nocb_gp_kthread) {
> > > - if (wake_gp)
> > > + if (wake_gp || rcu_nocb_poll)
> > > wake_up_process(rdp_gp->nocb_gp_kthread);
> > >
> > > /*
> > > @@ -1152,7 +1156,7 @@ static long rcu_nocb_rdp_offload(void *arg)
> > > * rcu_nocb_unlock() rcu_nocb_unlock()
> > > */
> > > wake_gp = rdp_offload_toggle(rdp, true, flags);
> > > - if (wake_gp)
> > > + if (wake_gp || rcu_nocb_poll)
> > > wake_up_process(rdp_gp->nocb_gp_kthread);
> > > swait_event_exclusive(rdp->nocb_state_wq,
> > > rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB) &&
> > > --
> > > 2.25.1
> > >
On Wed, Jun 08, 2022 at 01:01:31AM +0000, Zhang, Qiang1 wrote:
> On Wed, Jun 08, 2022 at 12:41:28AM +0000, Zhang, Qiang1 wrote:
> > On Tue, Jun 07, 2022 at 03:50:57PM +0800, Zqiang wrote:
> > > Currently, If the 'rcu_nocb_poll' bootargs is enable, all rcuog
> > > kthreads enter polling mode. however, due to only insert CPU's rdp
> > > which belong to rcu_nocb_mask to 'nocb_head_rdp' list or all CPU's
> > > rdp served by rcuog kthread have been de-offloaded, these cause
> > > the 'nocb_head_rdp' list served by rcuog kthread is empty, when
> > > the 'nocb_head_rdp' is empty, the rcuog kthread in polling mode
> > > not actually do anything. fix it by exiting polling mode when the
> > > 'nocb_head_rdp'list is empty, otherwise entering polling mode.
> > >
> > > Signed-off-by: Zqiang <[email protected]>
> > >
> > >This looks a bit more plausible, but what have you done to test this?
> >
> > Yes , I have only tested as follows and I added two trace events.
> >
> > + trace_rcu_nocb_wake(rcu_state.name, cpu,
> > + TPS("EnterNoPoll"));
> >
> > rcu_wait(READ_ONCE(my_rdp->nocb_toggling_rdp));
> > + trace_rcu_nocb_wake(rcu_state.name, cpu,
> > + TPS("ExitNoPoll"));
> >
> > runqemu kvm slirp nographic qemuparams="-m 2048 -smp 4"
> > bootparams="rcu_nocbs=2,3 rcutree.dump_tree=1 rcu_nocb_poll
> > rcutorture.nocbs_nthreads=4 rcutorture.test_boost=0" -d
Hi Paul, The test trace log is as follows:
rcuog/0-19 [003] ..... 169.400494: rcu_nocb_wake: rcu_preempt 0 EnterNoPoll
rcuog/0-19 [003] ..... 172.592072: rcu_nocb_wake: rcu_preempt 0 ExitNoPoll
rcuog/2-36 [002] ..... 173.553717: rcu_nocb_wake: rcu_preempt 2 EnterNoPoll
rcuog/2-36 [002] ..... 173.750084: rcu_nocb_wake: rcu_preempt 2 ExitNoPoll
Thanks
Zqiang
>
> >To exercise your change, could you please also add an appropriate value for the rcutorture.nocbs_nthreads kernel boot parameter? Without that boot parameter, your kernel will not actually offload or deoffload any CPUs.
>
> I have set ' rcutorture.nocbs_nthreads=4 ' in bootargs.
>
>I see it now, apologies for my confusion!
>
> Thanx, Paul
>
> >An alternative approach is to run rcutorture scenario TREE01.
>
> I will also use TREE01 for testing
>
> Thanks
> Zqiang
>
> >
> > Thanx, Paul
>
> > Thanks
> > Zqiang
> >
> > >
> > > Thanx, Paul
> > >
> > > ---
> > > v1->v2:
> > > Move rcu_nocb_poll flags check from rdp_offload_toggle() to
> > > rcu_nocb_rdp_offload/deoffload(), avoid unnecessary setting of
> > > rdp_gp->nocb_gp_sleep flags, because when rcu_nocb_poll is set
> > > the rdp_gp->nocb_gp_sleep is not used.
> > >
> > > kernel/rcu/tree_nocb.h | 16 ++++++++++------
> > > 1 file changed, 10 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index
> > > fa8e4f82e60c..2a52c9abc681 100644
> > > --- a/kernel/rcu/tree_nocb.h
> > > +++ b/kernel/rcu/tree_nocb.h
> > > @@ -698,10 +698,14 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
> > > TPS("WakeBypassIsDeferred"));
> > > }
> > > if (rcu_nocb_poll) {
> > > - /* Polling, so trace if first poll in the series. */
> > > - if (gotcbs)
> > > - trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
> > > - schedule_timeout_idle(1);
> > > + if (list_empty(&my_rdp->nocb_head_rdp)) {
> > > + rcu_wait(READ_ONCE(my_rdp->nocb_toggling_rdp));
> > > + } else {
> > > + /* Polling, so trace if first poll in the series. */
> > > + if (gotcbs)
> > > + trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
> > > + schedule_timeout_idle(1);
> > > + }
> > > } else if (!needwait_gp) {
> > > /* Wait for callbacks to appear. */
> > > trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Sleep")); @@
> > > -1030,7
> > > +1034,7 @@ static long rcu_nocb_rdp_deoffload(void *arg)
> > >
> > > mutex_lock(&rdp_gp->nocb_gp_kthread_mutex);
> > > if (rdp_gp->nocb_gp_kthread) {
> > > - if (wake_gp)
> > > + if (wake_gp || rcu_nocb_poll)
> > > wake_up_process(rdp_gp->nocb_gp_kthread);
> > >
> > > /*
> > > @@ -1152,7 +1156,7 @@ static long rcu_nocb_rdp_offload(void *arg)
> > > * rcu_nocb_unlock() rcu_nocb_unlock()
> > > */
> > > wake_gp = rdp_offload_toggle(rdp, true, flags);
> > > - if (wake_gp)
> > > + if (wake_gp || rcu_nocb_poll)
> > > wake_up_process(rdp_gp->nocb_gp_kthread);
> > > swait_event_exclusive(rdp->nocb_state_wq,
> > > rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB)
> > > &&
> > > --
> > > 2.25.1
> > >
On Wed, Jun 08, 2022 at 12:41:28AM +0000, Zhang, Qiang1 wrote:
> On Tue, Jun 07, 2022 at 03:50:57PM +0800, Zqiang wrote:
> > Currently, If the 'rcu_nocb_poll' bootargs is enable, all rcuog
> > kthreads enter polling mode. however, due to only insert CPU's rdp
> > which belong to rcu_nocb_mask to 'nocb_head_rdp' list or all CPU's
> > rdp served by rcuog kthread have been de-offloaded, these cause the
> > 'nocb_head_rdp' list served by rcuog kthread is empty, when the
> > 'nocb_head_rdp' is empty, the rcuog kthread in polling mode not
> > actually do anything. fix it by exiting polling mode when the
> > 'nocb_head_rdp'list is empty, otherwise entering polling mode.
> >
> > Signed-off-by: Zqiang <[email protected]>
> >
> >This looks a bit more plausible, but what have you done to test this?
>
> Yes , I have only tested as follows and I added two trace events.
>
> + trace_rcu_nocb_wake(rcu_state.name, cpu,
> + TPS("EnterNoPoll"));
>
> rcu_wait(READ_ONCE(my_rdp->nocb_toggling_rdp));
> + trace_rcu_nocb_wake(rcu_state.name, cpu,
> + TPS("ExitNoPoll"));
>
> runqemu kvm slirp nographic qemuparams="-m 2048 -smp 4"
> bootparams="rcu_nocbs=2,3 rcutree.dump_tree=1 rcu_nocb_poll
> rcutorture.nocbs_nthreads=4 rcutorture.test_boost=0" -d
>To exercise your change, could you please also add an appropriate value for the rcutorture.nocbs_nthreads kernel boot parameter? Without that boot parameter, your kernel will not actually offload or deoffload any CPUs.
I have set ' rcutorture.nocbs_nthreads=4 ' in bootargs.
>
>An alternative approach is to run rcutorture scenario TREE01.
I will also use TREE01 for testing
Thanks
Zqiang
>
> Thanx, Paul
> Thanks
> Zqiang
>
> >
> > Thanx, Paul
> >
> > ---
> > v1->v2:
> > Move rcu_nocb_poll flags check from rdp_offload_toggle() to
> > rcu_nocb_rdp_offload/deoffload(), avoid unnecessary setting of
> > rdp_gp->nocb_gp_sleep flags, because when rcu_nocb_poll is set the
> > rdp_gp->nocb_gp_sleep is not used.
> >
> > kernel/rcu/tree_nocb.h | 16 ++++++++++------
> > 1 file changed, 10 insertions(+), 6 deletions(-)
> >
> > diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index
> > fa8e4f82e60c..2a52c9abc681 100644
> > --- a/kernel/rcu/tree_nocb.h
> > +++ b/kernel/rcu/tree_nocb.h
> > @@ -698,10 +698,14 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
> > TPS("WakeBypassIsDeferred"));
> > }
> > if (rcu_nocb_poll) {
> > - /* Polling, so trace if first poll in the series. */
> > - if (gotcbs)
> > - trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
> > - schedule_timeout_idle(1);
> > + if (list_empty(&my_rdp->nocb_head_rdp)) {
> > + rcu_wait(READ_ONCE(my_rdp->nocb_toggling_rdp));
> > + } else {
> > + /* Polling, so trace if first poll in the series. */
> > + if (gotcbs)
> > + trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
> > + schedule_timeout_idle(1);
> > + }
> > } else if (!needwait_gp) {
> > /* Wait for callbacks to appear. */
> > trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Sleep")); @@
> > -1030,7
> > +1034,7 @@ static long rcu_nocb_rdp_deoffload(void *arg)
> >
> > mutex_lock(&rdp_gp->nocb_gp_kthread_mutex);
> > if (rdp_gp->nocb_gp_kthread) {
> > - if (wake_gp)
> > + if (wake_gp || rcu_nocb_poll)
> > wake_up_process(rdp_gp->nocb_gp_kthread);
> >
> > /*
> > @@ -1152,7 +1156,7 @@ static long rcu_nocb_rdp_offload(void *arg)
> > * rcu_nocb_unlock() rcu_nocb_unlock()
> > */
> > wake_gp = rdp_offload_toggle(rdp, true, flags);
> > - if (wake_gp)
> > + if (wake_gp || rcu_nocb_poll)
> > wake_up_process(rdp_gp->nocb_gp_kthread);
> > swait_event_exclusive(rdp->nocb_state_wq,
> > rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB) &&
> > --
> > 2.25.1
> >
On Tue, Jun 07, 2022 at 03:50:57PM +0800, Zqiang wrote:
> Currently, If the 'rcu_nocb_poll' bootargs is enable, all rcuog kthreads
> enter polling mode. however, due to only insert CPU's rdp which belong to
> rcu_nocb_mask to 'nocb_head_rdp' list or all CPU's rdp served by rcuog
> kthread have been de-offloaded, these cause the 'nocb_head_rdp' list
> served by rcuog kthread is empty, when the 'nocb_head_rdp' is empty,
> the rcuog kthread in polling mode not actually do anything. fix it by
> exiting polling mode when the 'nocb_head_rdp'list is empty, otherwise
> entering polling mode.
>
> Signed-off-by: Zqiang <[email protected]>
> ---
> v1->v2:
> Move rcu_nocb_poll flags check from rdp_offload_toggle() to
> rcu_nocb_rdp_offload/deoffload(), avoid unnecessary setting of
> rdp_gp->nocb_gp_sleep flags, because when rcu_nocb_poll is set
> the rdp_gp->nocb_gp_sleep is not used.
>
> kernel/rcu/tree_nocb.h | 16 ++++++++++------
> 1 file changed, 10 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
> index fa8e4f82e60c..2a52c9abc681 100644
> --- a/kernel/rcu/tree_nocb.h
> +++ b/kernel/rcu/tree_nocb.h
> @@ -698,10 +698,14 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
> TPS("WakeBypassIsDeferred"));
> }
> if (rcu_nocb_poll) {
> - /* Polling, so trace if first poll in the series. */
> - if (gotcbs)
> - trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
> - schedule_timeout_idle(1);
> + if (list_empty(&my_rdp->nocb_head_rdp)) {
> + rcu_wait(READ_ONCE(my_rdp->nocb_toggling_rdp));
I suspect you have based your patch on upstream tree which doesn't seem
to have this one yet:
"rcu/nocb: Add/del rdp to iterate from rcuog itself"
With this patch you can't wait on changes to my_rdp->nocb_toggling_rdp because
nocb_gp_wait() now performs the list_add/list_del itself.
Please rebase your patch on top of latest rcu:dev from Paul's tree. Then
all you need to do is to change the wait side, something like this (untested):
diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index fa8e4f82e60c..f36d6be4f372 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -584,6 +584,15 @@ static int nocb_gp_toggle_rdp(struct rcu_data *rdp,
return ret;
}
+static void nocb_gp_sleep(struct rdp *my_rdp, int cpu)
+{
+ trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Sleep"));
+ swait_event_interruptible_exclusive(my_rdp->nocb_gp_wq,
+ !READ_ONCE(my_rdp->nocb_gp_sleep));
+ trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("EndSleep"));
+}
+
+
/*
* No-CBs GP kthreads come here to wait for additional callbacks to show up
* or for grace periods to end.
@@ -701,13 +710,19 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
/* Polling, so trace if first poll in the series. */
if (gotcbs)
trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
- schedule_timeout_idle(1);
+ if (list_empty(&my_rdp->nocb_head_rdp)) {
+ raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
+ if (!my_rdp->nocb_toggling_rdp)
+ WRITE_ONCE(my_rdp->nocb_gp_sleep, true);
+ raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
+ /* Wait for any offloading rdp */
+ rdp_gp_sleep(my_rdp, cpu);
+ } else {
+ schedule_timeout_idle(1);
+ }
} else if (!needwait_gp) {
/* Wait for callbacks to appear. */
- trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Sleep"));
- swait_event_interruptible_exclusive(my_rdp->nocb_gp_wq,
- !READ_ONCE(my_rdp->nocb_gp_sleep));
- trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("EndSleep"));
+ rdp_gp_sleep(my_rdp, cpu);
} else {
rnp = my_rdp->mynode;
trace_rcu_this_gp(rnp, my_rdp, wait_gp_seq, TPS("StartWait"));
On Tue, Jun 07, 2022 at 03:50:57PM +0800, Zqiang wrote:
> Currently, If the 'rcu_nocb_poll' bootargs is enable, all rcuog
> kthreads enter polling mode. however, due to only insert CPU's rdp
> which belong to rcu_nocb_mask to 'nocb_head_rdp' list or all CPU's rdp
> served by rcuog kthread have been de-offloaded, these cause the
> 'nocb_head_rdp' list served by rcuog kthread is empty, when the
> 'nocb_head_rdp' is empty, the rcuog kthread in polling mode not
> actually do anything. fix it by exiting polling mode when the
> 'nocb_head_rdp'list is empty, otherwise entering polling mode.
>
> Signed-off-by: Zqiang <[email protected]>
> ---
> v1->v2:
> Move rcu_nocb_poll flags check from rdp_offload_toggle() to
> rcu_nocb_rdp_offload/deoffload(), avoid unnecessary setting of
> rdp_gp->nocb_gp_sleep flags, because when rcu_nocb_poll is set the
> rdp_gp->nocb_gp_sleep is not used.
>
> kernel/rcu/tree_nocb.h | 16 ++++++++++------
> 1 file changed, 10 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index
> fa8e4f82e60c..2a52c9abc681 100644
> --- a/kernel/rcu/tree_nocb.h
> +++ b/kernel/rcu/tree_nocb.h
> @@ -698,10 +698,14 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
> TPS("WakeBypassIsDeferred"));
> }
> if (rcu_nocb_poll) {
> - /* Polling, so trace if first poll in the series. */
> - if (gotcbs)
> - trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
> - schedule_timeout_idle(1);
> + if (list_empty(&my_rdp->nocb_head_rdp)) {
> + rcu_wait(READ_ONCE(my_rdp->nocb_toggling_rdp));
>I suspect you have based your patch on upstream tree which doesn't seem to have this one yet:
>
> "rcu/nocb: Add/del rdp to iterate from rcuog itself"
>
>With this patch you can't wait on changes to my_rdp->nocb_toggling_rdp because
>nocb_gp_wait() now performs the list_add/list_del itself.
>
>Please rebase your patch on top of latest rcu:dev from Paul's tree. Then all you need to do is to change the wait side, something like this (untested):
Hi Frederic thanks for your advice.
This is similar to what I said in my previous email, this change is better, I will test it.
Thanks
Zqiang
>
>diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index fa8e4f82e60c..f36d6be4f372 100644
>--- a/kernel/rcu/tree_nocb.h
>+++ b/kernel/rcu/tree_nocb.h
>@@ -584,6 +584,15 @@ static int nocb_gp_toggle_rdp(struct rcu_data *rdp,
> return ret;
> }
>
>+static void nocb_gp_sleep(struct rdp *my_rdp, int cpu) {
>+ trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Sleep"));
>+ swait_event_interruptible_exclusive(my_rdp->nocb_gp_wq,
>+ !READ_ONCE(my_rdp->nocb_gp_sleep));
>+ trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("EndSleep")); }
>+
>+
> /*
> * No-CBs GP kthreads come here to wait for additional callbacks to show up
> * or for grace periods to end.
>@@ -701,13 +710,19 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
> /* Polling, so trace if first poll in the series. */
> if (gotcbs)
> trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
>- schedule_timeout_idle(1);
>+ if (list_empty(&my_rdp->nocb_head_rdp)) {
>+ raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
>+ if (!my_rdp->nocb_toggling_rdp)
>+ WRITE_ONCE(my_rdp->nocb_gp_sleep, true);
>+ raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
>+ /* Wait for any offloading rdp */
>+ rdp_gp_sleep(my_rdp, cpu);
>+ } else {
>+ schedule_timeout_idle(1);
>+ }
> } else if (!needwait_gp) {
> /* Wait for callbacks to appear. */
>- trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Sleep"));
>- swait_event_interruptible_exclusive(my_rdp->nocb_gp_wq,
>- !READ_ONCE(my_rdp->nocb_gp_sleep));
>- trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("EndSleep"));
>+ rdp_gp_sleep(my_rdp, cpu);
> } else {
> rnp = my_rdp->mynode;
>
> trace_rcu_this_gp(rnp, my_rdp, wait_gp_seq, TPS("StartWait"));