| Message ID | 20220520084155.1745726-1-qiang1.zhang@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] rcu-tasks: Stop RCU Tasks scanning tasks which record on dyntick-idle entry | expand |
On Fri, May 20, 2022 at 04:41:55PM +0800, Zqiang wrote: > When the RCU Tasks scanning on-rq tasks, there is no need to scanning > tasks which record on dyntick-idle entry, at this time, these tasks are > not remain within an RCU Tasks read-side critical section. > > This commit skip scanning tasks which record on dyntick-idle entry in > rcu_tasks_pertask(). > > Reported-by: kernel test robot <lkp@intel.com> > Signed-off-by: Zqiang <qiang1.zhang@intel.com> You lost me with this one. Doesn't the rcu_tasks_pertask() function already exclude the idle tasks that might possibly be running in dyntick-idle state in non-CONFIG_NO_HZ_FULL systems? What am I missing here? Thanx, Paul > --- > v1->v2: > fix build test ERROR due to CONFIG_TASKS_RCU=n > > kernel/rcu/tasks.h | 12 +++++++++--- > 1 file changed, 9 insertions(+), 3 deletions(-) > > diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h > index f6459343e4b6..7cb0f922478e 100644 > --- a/kernel/rcu/tasks.h > +++ b/kernel/rcu/tasks.h > @@ -809,10 +809,17 @@ static void rcu_tasks_pregp_step(struct list_head *hop) > synchronize_rcu(); > } > > +static bool task_is_on_dyntick_idle(struct task_struct *t) > +{ > + return IS_ENABLED(CONFIG_NO_HZ_FULL) && !is_idle_task(t) && > + t->rcu_tasks_idle_cpu >= 0; > +} > + > /* Per-task initial processing. */ > static void rcu_tasks_pertask(struct task_struct *t, struct list_head *hop) > { > - if (t != current && READ_ONCE(t->on_rq) && !is_idle_task(t)) { > + if (t != current && READ_ONCE(t->on_rq) && !is_idle_task(t) && > + !task_is_on_dyntick_idle(t)) { > get_task_struct(t); > t->rcu_tasks_nvcsw = READ_ONCE(t->nvcsw); > WRITE_ONCE(t->rcu_tasks_holdout, true); > @@ -842,8 +849,7 @@ static void check_holdout_task(struct task_struct *t, > if (!READ_ONCE(t->rcu_tasks_holdout) || > t->rcu_tasks_nvcsw != READ_ONCE(t->nvcsw) || > !READ_ONCE(t->on_rq) || > - (IS_ENABLED(CONFIG_NO_HZ_FULL) && > - !is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) { > + task_is_on_dyntick_idle(t)) { > WRITE_ONCE(t->rcu_tasks_holdout, false); > list_del_init(&t->rcu_tasks_holdout_list); > put_task_struct(t); > -- > 2.25.1 >
On Fri, May 20, 2022 at 04:41:55PM +0800, Zqiang wrote: > When the RCU Tasks scanning on-rq tasks, there is no need to scanning > tasks which record on dyntick-idle entry, at this time, these tasks > are not remain within an RCU Tasks read-side critical section. > > This commit skip scanning tasks which record on dyntick-idle entry in > rcu_tasks_pertask(). > > Reported-by: kernel test robot <lkp@intel.com> > Signed-off-by: Zqiang <qiang1.zhang@intel.com> > >You lost me with this one. Doesn't the rcu_tasks_pertask() function already exclude the idle tasks that might possibly be running in dyntick-idle state in non-CONFIG_NO_HZ_FULL systems? > >What am I missing here? Thanks for reply. Yes, the is_idle_task() can remove from task_is_on_dyntick_idle(). And the is_idle_task() can also remove from warnings in check_holdout_task(), because the rcu _tasks_pertask() already exclude the idle tasks. Is my understanding correct? Thanks Zqiang > Thanx, Paul > > --- > v1->v2: > fix build test ERROR due to CONFIG_TASKS_RCU=n > > kernel/rcu/tasks.h | 12 +++++++++--- > 1 file changed, 9 insertions(+), 3 deletions(-) > > diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index > f6459343e4b6..7cb0f922478e 100644 > --- a/kernel/rcu/tasks.h > +++ b/kernel/rcu/tasks.h > @@ -809,10 +809,17 @@ static void rcu_tasks_pregp_step(struct list_head *hop) > synchronize_rcu(); > } > > +static bool task_is_on_dyntick_idle(struct task_struct *t) { > + return IS_ENABLED(CONFIG_NO_HZ_FULL) && !is_idle_task(t) && > + t->rcu_tasks_idle_cpu >= 0; > +} > + > /* Per-task initial processing. */ > static void rcu_tasks_pertask(struct task_struct *t, struct list_head > *hop) { > - if (t != current && READ_ONCE(t->on_rq) && !is_idle_task(t)) { > + if (t != current && READ_ONCE(t->on_rq) && !is_idle_task(t) && > + !task_is_on_dyntick_idle(t)) { > get_task_struct(t); > t->rcu_tasks_nvcsw = READ_ONCE(t->nvcsw); > WRITE_ONCE(t->rcu_tasks_holdout, true); @@ -842,8 +849,7 @@ static > void check_holdout_task(struct task_struct *t, > if (!READ_ONCE(t->rcu_tasks_holdout) || > t->rcu_tasks_nvcsw != READ_ONCE(t->nvcsw) || > !READ_ONCE(t->on_rq) || > - (IS_ENABLED(CONFIG_NO_HZ_FULL) && > - !is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) { > + task_is_on_dyntick_idle(t)) { > WRITE_ONCE(t->rcu_tasks_holdout, false); > list_del_init(&t->rcu_tasks_holdout_list); > put_task_struct(t); > -- > 2.25.1 >
diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index f6459343e4b6..7cb0f922478e 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -809,10 +809,17 @@ static void rcu_tasks_pregp_step(struct list_head *hop) synchronize_rcu(); } +static bool task_is_on_dyntick_idle(struct task_struct *t) +{ + return IS_ENABLED(CONFIG_NO_HZ_FULL) && !is_idle_task(t) && + t->rcu_tasks_idle_cpu >= 0; +} + /* Per-task initial processing. */ static void rcu_tasks_pertask(struct task_struct *t, struct list_head *hop) { - if (t != current && READ_ONCE(t->on_rq) && !is_idle_task(t)) { + if (t != current && READ_ONCE(t->on_rq) && !is_idle_task(t) && + !task_is_on_dyntick_idle(t)) { get_task_struct(t); t->rcu_tasks_nvcsw = READ_ONCE(t->nvcsw); WRITE_ONCE(t->rcu_tasks_holdout, true); @@ -842,8 +849,7 @@ static void check_holdout_task(struct task_struct *t, if (!READ_ONCE(t->rcu_tasks_holdout) || t->rcu_tasks_nvcsw != READ_ONCE(t->nvcsw) || !READ_ONCE(t->on_rq) || - (IS_ENABLED(CONFIG_NO_HZ_FULL) && - !is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) { + task_is_on_dyntick_idle(t)) { WRITE_ONCE(t->rcu_tasks_holdout, false); list_del_init(&t->rcu_tasks_holdout_list); put_task_struct(t);
When the RCU Tasks scanning on-rq tasks, there is no need to scanning tasks which record on dyntick-idle entry, at this time, these tasks are not remain within an RCU Tasks read-side critical section. This commit skip scanning tasks which record on dyntick-idle entry in rcu_tasks_pertask(). Reported-by: kernel test robot <lkp@intel.com> Signed-off-by: Zqiang <qiang1.zhang@intel.com> --- v1->v2: fix build test ERROR due to CONFIG_TASKS_RCU=n kernel/rcu/tasks.h | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-)