Re: [PATCH v2] sched/fair: enqueue_task_fair optimization
On Wed, May 13, 2020 at 03:25:29PM +0200 Vincent Guittot wrote:
> On Wed, 13 May 2020 at 15:18, Phil Auld wrote:
> >
> > On Wed, May 13, 2020 at 03:15:53PM +0200 Vincent Guittot wrote:
> > > On Wed, 13 May 2020 at 15:13, Phil Auld wrote:
> > > >
> > > > On Wed, May 13, 2020 at 03:10:28PM +0200 Vincent Guittot wrote:
> > > > > On Wed, 13 May 2020 at 14:45, Phil Auld wrote:
> > > > > >
> > > > > > Hi Vincent,
> > > > > >
> > > > > > On Wed, May 13, 2020 at 02:33:35PM +0200 Vincent Guittot wrote:
> > > > > > > enqueue_task_fair jumps to enqueue_throttle label when
> > > > > > > cfs_rq_of(se) is
> > > > > > > throttled which means that se can't be NULL and we can skip the
> > > > > > > test.
> > > > > > >
> > > > > >
> > > > > > s/be NULL/be non-NULL/
> > > > > >
> > > > > > I think.
> > > > >
> > > > > This sentence refers to the move of enqueue_throttle and the fact that
> > > > > se can't be null when goto enqueue_throttle and we can jump directly
> > > > > after the if statement, which is now removed in v2 because se is
> > > > > always NULL if we don't use goto enqueue_throttle.
> > > > >
> > > > > I haven't change the commit message for the remove of if statement
> > > > >
> > > >
> > > > Fair enough, it just seems backwards from the intent of the patch now.
> > > >
> > > > There is also an extra } after the update_overutilized_status.
> > >
> > > don't know what I did but it's crap. sorry about that
> > >
> >
> > No worries. I didn't see it when I read it either. The compiler told me :)
>
> Yeah, but i thought that i compiled it which is obviously not true
>
It's that "obviously" correct stuff that bites you every time ;)
> >
> >
> > > Let me prepare a v3
> > >
> > > >
> > > >
> > > > Cheers,
> > > > Phil
> > > >
> > > >
> > > >
> > > > > >
> > > > > > It's more like if it doesn't jump to the label then se must be NULL
> > > > > > for
> > > > > > the loop to terminate. The final loop is a NOP if se is NULL. The
> > > > > > check
> > > > > > wasn't protecting that.
> > > > > >
> > > > > > Otherwise still
> > > > > >
> > > > > > > Reviewed-by: Phil Auld
> > > > > >
> > > > > > Cheers,
> > > > > > Phil
> > > > > >
> > > > > >
> > > > > > > Signed-off-by: Vincent Guittot
> > > > > > > ---
> > > > > > >
> > > > > > > v2 changes:
> > > > > > > - Remove useless if statement
> > > > > > >
> > > > > > > kernel/sched/fair.c | 39 ---
> > > > > > > 1 file changed, 20 insertions(+), 19 deletions(-)
> > > > > > >
> > > > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > > > > > > index a0c690d57430..b51b12d63c39 100644
> > > > > > > --- a/kernel/sched/fair.c
> > > > > > > +++ b/kernel/sched/fair.c
> > > > > > > @@ -5513,28 +5513,29 @@ enqueue_task_fair(struct rq *rq, struct
> > > > > > > task_struct *p, int flags)
> > > > > > > list_add_leaf_cfs_rq(cfs_rq);
> > > > > > > }
> > > > > > >
> > > > > > > -enqueue_throttle:
> > > > > > > - if (!se) {
> > > > > > > - add_nr_running(rq, 1);
> > > > > > > - /*
> > > > > > > - * Since new tasks are assigned an initial util_avg
> > > > > > > equal to
> > > > > > > - * half of the spare capacity of their CPU, tiny
> > > > > > > tasks have the
> > > > > > > - * ability to cross the overutilized threshold,
> > > > > > > which will
> > > > > > > - * result in the load balancer ruining all the task
> > > > > > > placement
> > > > > > > - * done by EAS. As a way to mitigate that effect,
> > > > > > > do not account
> > > > > > > - * for the first enqueue operation of new tasks
> > > > > > > during the
> > > > > > > - * overutilized flag detection.
> > > > > > > - *
> > > > > > > - * A better way of solving this problem would be to
> > > > > > > wait for
> > > > > > > - * the PELT signals of tasks to converge before
> > > > > > > taking them
> > > > > > > - * into account, but that is not straightforward to
> > > > > > > implement,
> > > > > > > - * and the following generally works well enough in
> > > > > > > practice.
> > > > > > > - */
> > > > > > > - if (flags & ENQUEUE_WAKEUP)
> > > > > > > - update_overutilized_status(rq);
> > > > > > > + /* At this point se is NULL and we are at root level*/
> > > > > > > + add_nr_running(rq, 1);
> > > > > > > +
> > > > > > > + /*
> > > > > > > + * Since new tasks are assigned an initial util_avg equal to
> > > > > > > + * half of the spare capacity of their CPU, tiny tasks have
> > > > > > > the
> > > > > > > + * ability to cross the overutilized threshold, which will
> > > > > > > + * result in the load balancer ruining all the task
> > > > > > > placement
> > > > > > > + * done by EAS. As a way to mitigate that effect, do not
> > > > > > > account
> > > > > > > +
Re: [PATCH v2] sched/fair: enqueue_task_fair optimization
On Wed, 13 May 2020 at 15:18, Phil Auld wrote:
>
> On Wed, May 13, 2020 at 03:15:53PM +0200 Vincent Guittot wrote:
> > On Wed, 13 May 2020 at 15:13, Phil Auld wrote:
> > >
> > > On Wed, May 13, 2020 at 03:10:28PM +0200 Vincent Guittot wrote:
> > > > On Wed, 13 May 2020 at 14:45, Phil Auld wrote:
> > > > >
> > > > > Hi Vincent,
> > > > >
> > > > > On Wed, May 13, 2020 at 02:33:35PM +0200 Vincent Guittot wrote:
> > > > > > enqueue_task_fair jumps to enqueue_throttle label when
> > > > > > cfs_rq_of(se) is
> > > > > > throttled which means that se can't be NULL and we can skip the
> > > > > > test.
> > > > > >
> > > > >
> > > > > s/be NULL/be non-NULL/
> > > > >
> > > > > I think.
> > > >
> > > > This sentence refers to the move of enqueue_throttle and the fact that
> > > > se can't be null when goto enqueue_throttle and we can jump directly
> > > > after the if statement, which is now removed in v2 because se is
> > > > always NULL if we don't use goto enqueue_throttle.
> > > >
> > > > I haven't change the commit message for the remove of if statement
> > > >
> > >
> > > Fair enough, it just seems backwards from the intent of the patch now.
> > >
> > > There is also an extra } after the update_overutilized_status.
> >
> > don't know what I did but it's crap. sorry about that
> >
>
> No worries. I didn't see it when I read it either. The compiler told me :)
Yeah, but i thought that i compiled it which is obviously not true
>
>
> > Let me prepare a v3
> >
> > >
> > >
> > > Cheers,
> > > Phil
> > >
> > >
> > >
> > > > >
> > > > > It's more like if it doesn't jump to the label then se must be NULL
> > > > > for
> > > > > the loop to terminate. The final loop is a NOP if se is NULL. The
> > > > > check
> > > > > wasn't protecting that.
> > > > >
> > > > > Otherwise still
> > > > >
> > > > > > Reviewed-by: Phil Auld
> > > > >
> > > > > Cheers,
> > > > > Phil
> > > > >
> > > > >
> > > > > > Signed-off-by: Vincent Guittot
> > > > > > ---
> > > > > >
> > > > > > v2 changes:
> > > > > > - Remove useless if statement
> > > > > >
> > > > > > kernel/sched/fair.c | 39 ---
> > > > > > 1 file changed, 20 insertions(+), 19 deletions(-)
> > > > > >
> > > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > > > > > index a0c690d57430..b51b12d63c39 100644
> > > > > > --- a/kernel/sched/fair.c
> > > > > > +++ b/kernel/sched/fair.c
> > > > > > @@ -5513,28 +5513,29 @@ enqueue_task_fair(struct rq *rq, struct
> > > > > > task_struct *p, int flags)
> > > > > > list_add_leaf_cfs_rq(cfs_rq);
> > > > > > }
> > > > > >
> > > > > > -enqueue_throttle:
> > > > > > - if (!se) {
> > > > > > - add_nr_running(rq, 1);
> > > > > > - /*
> > > > > > - * Since new tasks are assigned an initial util_avg
> > > > > > equal to
> > > > > > - * half of the spare capacity of their CPU, tiny
> > > > > > tasks have the
> > > > > > - * ability to cross the overutilized threshold, which
> > > > > > will
> > > > > > - * result in the load balancer ruining all the task
> > > > > > placement
> > > > > > - * done by EAS. As a way to mitigate that effect, do
> > > > > > not account
> > > > > > - * for the first enqueue operation of new tasks
> > > > > > during the
> > > > > > - * overutilized flag detection.
> > > > > > - *
> > > > > > - * A better way of solving this problem would be to
> > > > > > wait for
> > > > > > - * the PELT signals of tasks to converge before
> > > > > > taking them
> > > > > > - * into account, but that is not straightforward to
> > > > > > implement,
> > > > > > - * and the following generally works well enough in
> > > > > > practice.
> > > > > > - */
> > > > > > - if (flags & ENQUEUE_WAKEUP)
> > > > > > - update_overutilized_status(rq);
> > > > > > + /* At this point se is NULL and we are at root level*/
> > > > > > + add_nr_running(rq, 1);
> > > > > > +
> > > > > > + /*
> > > > > > + * Since new tasks are assigned an initial util_avg equal to
> > > > > > + * half of the spare capacity of their CPU, tiny tasks have
> > > > > > the
> > > > > > + * ability to cross the overutilized threshold, which will
> > > > > > + * result in the load balancer ruining all the task placement
> > > > > > + * done by EAS. As a way to mitigate that effect, do not
> > > > > > account
> > > > > > + * for the first enqueue operation of new tasks during the
> > > > > > + * overutilized flag detection.
> > > > > > + *
> > > > > > + * A better way of solving this problem would be to wait for
> > > > > > + * the PELT signals of tasks to converge before taking them
> > > > > > + * into account, but that is not straightforward to implement,
> > > > > > + * and
Re: [PATCH v2] sched/fair: enqueue_task_fair optimization
On Wed, May 13, 2020 at 03:15:53PM +0200 Vincent Guittot wrote:
> On Wed, 13 May 2020 at 15:13, Phil Auld wrote:
> >
> > On Wed, May 13, 2020 at 03:10:28PM +0200 Vincent Guittot wrote:
> > > On Wed, 13 May 2020 at 14:45, Phil Auld wrote:
> > > >
> > > > Hi Vincent,
> > > >
> > > > On Wed, May 13, 2020 at 02:33:35PM +0200 Vincent Guittot wrote:
> > > > > enqueue_task_fair jumps to enqueue_throttle label when cfs_rq_of(se)
> > > > > is
> > > > > throttled which means that se can't be NULL and we can skip the test.
> > > > >
> > > >
> > > > s/be NULL/be non-NULL/
> > > >
> > > > I think.
> > >
> > > This sentence refers to the move of enqueue_throttle and the fact that
> > > se can't be null when goto enqueue_throttle and we can jump directly
> > > after the if statement, which is now removed in v2 because se is
> > > always NULL if we don't use goto enqueue_throttle.
> > >
> > > I haven't change the commit message for the remove of if statement
> > >
> >
> > Fair enough, it just seems backwards from the intent of the patch now.
> >
> > There is also an extra } after the update_overutilized_status.
>
> don't know what I did but it's crap. sorry about that
>
No worries. I didn't see it when I read it either. The compiler told me :)
> Let me prepare a v3
>
> >
> >
> > Cheers,
> > Phil
> >
> >
> >
> > > >
> > > > It's more like if it doesn't jump to the label then se must be NULL for
> > > > the loop to terminate. The final loop is a NOP if se is NULL. The check
> > > > wasn't protecting that.
> > > >
> > > > Otherwise still
> > > >
> > > > > Reviewed-by: Phil Auld
> > > >
> > > > Cheers,
> > > > Phil
> > > >
> > > >
> > > > > Signed-off-by: Vincent Guittot
> > > > > ---
> > > > >
> > > > > v2 changes:
> > > > > - Remove useless if statement
> > > > >
> > > > > kernel/sched/fair.c | 39 ---
> > > > > 1 file changed, 20 insertions(+), 19 deletions(-)
> > > > >
> > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > > > > index a0c690d57430..b51b12d63c39 100644
> > > > > --- a/kernel/sched/fair.c
> > > > > +++ b/kernel/sched/fair.c
> > > > > @@ -5513,28 +5513,29 @@ enqueue_task_fair(struct rq *rq, struct
> > > > > task_struct *p, int flags)
> > > > > list_add_leaf_cfs_rq(cfs_rq);
> > > > > }
> > > > >
> > > > > -enqueue_throttle:
> > > > > - if (!se) {
> > > > > - add_nr_running(rq, 1);
> > > > > - /*
> > > > > - * Since new tasks are assigned an initial util_avg
> > > > > equal to
> > > > > - * half of the spare capacity of their CPU, tiny tasks
> > > > > have the
> > > > > - * ability to cross the overutilized threshold, which
> > > > > will
> > > > > - * result in the load balancer ruining all the task
> > > > > placement
> > > > > - * done by EAS. As a way to mitigate that effect, do
> > > > > not account
> > > > > - * for the first enqueue operation of new tasks during
> > > > > the
> > > > > - * overutilized flag detection.
> > > > > - *
> > > > > - * A better way of solving this problem would be to
> > > > > wait for
> > > > > - * the PELT signals of tasks to converge before taking
> > > > > them
> > > > > - * into account, but that is not straightforward to
> > > > > implement,
> > > > > - * and the following generally works well enough in
> > > > > practice.
> > > > > - */
> > > > > - if (flags & ENQUEUE_WAKEUP)
> > > > > - update_overutilized_status(rq);
> > > > > + /* At this point se is NULL and we are at root level*/
> > > > > + add_nr_running(rq, 1);
> > > > > +
> > > > > + /*
> > > > > + * Since new tasks are assigned an initial util_avg equal to
> > > > > + * half of the spare capacity of their CPU, tiny tasks have the
> > > > > + * ability to cross the overutilized threshold, which will
> > > > > + * result in the load balancer ruining all the task placement
> > > > > + * done by EAS. As a way to mitigate that effect, do not account
> > > > > + * for the first enqueue operation of new tasks during the
> > > > > + * overutilized flag detection.
> > > > > + *
> > > > > + * A better way of solving this problem would be to wait for
> > > > > + * the PELT signals of tasks to converge before taking them
> > > > > + * into account, but that is not straightforward to implement,
> > > > > + * and the following generally works well enough in practice.
> > > > > + */
> > > > > + if (flags & ENQUEUE_WAKEUP)
> > > > > + update_overutilized_status(rq);
> > > > >
> > > > > }
> > > > >
> > > > > +enqueue_throttle:
> > > > > if (cfs_bandwidth_used()) {
> > > > > /*
> > > > >* When bandwidth control is enabled; the
> > > > > cfs_rq_throttled()
> > > > >
Re: [PATCH v2] sched/fair: enqueue_task_fair optimization
On Wed, 13 May 2020 at 15:13, Phil Auld wrote:
>
> On Wed, May 13, 2020 at 03:10:28PM +0200 Vincent Guittot wrote:
> > On Wed, 13 May 2020 at 14:45, Phil Auld wrote:
> > >
> > > Hi Vincent,
> > >
> > > On Wed, May 13, 2020 at 02:33:35PM +0200 Vincent Guittot wrote:
> > > > enqueue_task_fair jumps to enqueue_throttle label when cfs_rq_of(se) is
> > > > throttled which means that se can't be NULL and we can skip the test.
> > > >
> > >
> > > s/be NULL/be non-NULL/
> > >
> > > I think.
> >
> > This sentence refers to the move of enqueue_throttle and the fact that
> > se can't be null when goto enqueue_throttle and we can jump directly
> > after the if statement, which is now removed in v2 because se is
> > always NULL if we don't use goto enqueue_throttle.
> >
> > I haven't change the commit message for the remove of if statement
> >
>
> Fair enough, it just seems backwards from the intent of the patch now.
>
> There is also an extra } after the update_overutilized_status.
don't know what I did but it's crap. sorry about that
Let me prepare a v3
>
>
> Cheers,
> Phil
>
>
>
> > >
> > > It's more like if it doesn't jump to the label then se must be NULL for
> > > the loop to terminate. The final loop is a NOP if se is NULL. The check
> > > wasn't protecting that.
> > >
> > > Otherwise still
> > >
> > > > Reviewed-by: Phil Auld
> > >
> > > Cheers,
> > > Phil
> > >
> > >
> > > > Signed-off-by: Vincent Guittot
> > > > ---
> > > >
> > > > v2 changes:
> > > > - Remove useless if statement
> > > >
> > > > kernel/sched/fair.c | 39 ---
> > > > 1 file changed, 20 insertions(+), 19 deletions(-)
> > > >
> > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > > > index a0c690d57430..b51b12d63c39 100644
> > > > --- a/kernel/sched/fair.c
> > > > +++ b/kernel/sched/fair.c
> > > > @@ -5513,28 +5513,29 @@ enqueue_task_fair(struct rq *rq, struct
> > > > task_struct *p, int flags)
> > > > list_add_leaf_cfs_rq(cfs_rq);
> > > > }
> > > >
> > > > -enqueue_throttle:
> > > > - if (!se) {
> > > > - add_nr_running(rq, 1);
> > > > - /*
> > > > - * Since new tasks are assigned an initial util_avg equal
> > > > to
> > > > - * half of the spare capacity of their CPU, tiny tasks
> > > > have the
> > > > - * ability to cross the overutilized threshold, which will
> > > > - * result in the load balancer ruining all the task
> > > > placement
> > > > - * done by EAS. As a way to mitigate that effect, do not
> > > > account
> > > > - * for the first enqueue operation of new tasks during the
> > > > - * overutilized flag detection.
> > > > - *
> > > > - * A better way of solving this problem would be to wait
> > > > for
> > > > - * the PELT signals of tasks to converge before taking
> > > > them
> > > > - * into account, but that is not straightforward to
> > > > implement,
> > > > - * and the following generally works well enough in
> > > > practice.
> > > > - */
> > > > - if (flags & ENQUEUE_WAKEUP)
> > > > - update_overutilized_status(rq);
> > > > + /* At this point se is NULL and we are at root level*/
> > > > + add_nr_running(rq, 1);
> > > > +
> > > > + /*
> > > > + * Since new tasks are assigned an initial util_avg equal to
> > > > + * half of the spare capacity of their CPU, tiny tasks have the
> > > > + * ability to cross the overutilized threshold, which will
> > > > + * result in the load balancer ruining all the task placement
> > > > + * done by EAS. As a way to mitigate that effect, do not account
> > > > + * for the first enqueue operation of new tasks during the
> > > > + * overutilized flag detection.
> > > > + *
> > > > + * A better way of solving this problem would be to wait for
> > > > + * the PELT signals of tasks to converge before taking them
> > > > + * into account, but that is not straightforward to implement,
> > > > + * and the following generally works well enough in practice.
> > > > + */
> > > > + if (flags & ENQUEUE_WAKEUP)
> > > > + update_overutilized_status(rq);
> > > >
> > > > }
> > > >
> > > > +enqueue_throttle:
> > > > if (cfs_bandwidth_used()) {
> > > > /*
> > > >* When bandwidth control is enabled; the
> > > > cfs_rq_throttled()
> > > > --
> > > > 2.17.1
> > > >
> > >
> > > --
> > >
> >
>
> --
>
Re: [PATCH v2] sched/fair: enqueue_task_fair optimization
On Wed, May 13, 2020 at 03:10:28PM +0200 Vincent Guittot wrote:
> On Wed, 13 May 2020 at 14:45, Phil Auld wrote:
> >
> > Hi Vincent,
> >
> > On Wed, May 13, 2020 at 02:33:35PM +0200 Vincent Guittot wrote:
> > > enqueue_task_fair jumps to enqueue_throttle label when cfs_rq_of(se) is
> > > throttled which means that se can't be NULL and we can skip the test.
> > >
> >
> > s/be NULL/be non-NULL/
> >
> > I think.
>
> This sentence refers to the move of enqueue_throttle and the fact that
> se can't be null when goto enqueue_throttle and we can jump directly
> after the if statement, which is now removed in v2 because se is
> always NULL if we don't use goto enqueue_throttle.
>
> I haven't change the commit message for the remove of if statement
>
Fair enough, it just seems backwards from the intent of the patch now.
There is also an extra } after the update_overutilized_status.
Cheers,
Phil
> >
> > It's more like if it doesn't jump to the label then se must be NULL for
> > the loop to terminate. The final loop is a NOP if se is NULL. The check
> > wasn't protecting that.
> >
> > Otherwise still
> >
> > > Reviewed-by: Phil Auld
> >
> > Cheers,
> > Phil
> >
> >
> > > Signed-off-by: Vincent Guittot
> > > ---
> > >
> > > v2 changes:
> > > - Remove useless if statement
> > >
> > > kernel/sched/fair.c | 39 ---
> > > 1 file changed, 20 insertions(+), 19 deletions(-)
> > >
> > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > > index a0c690d57430..b51b12d63c39 100644
> > > --- a/kernel/sched/fair.c
> > > +++ b/kernel/sched/fair.c
> > > @@ -5513,28 +5513,29 @@ enqueue_task_fair(struct rq *rq, struct
> > > task_struct *p, int flags)
> > > list_add_leaf_cfs_rq(cfs_rq);
> > > }
> > >
> > > -enqueue_throttle:
> > > - if (!se) {
> > > - add_nr_running(rq, 1);
> > > - /*
> > > - * Since new tasks are assigned an initial util_avg equal to
> > > - * half of the spare capacity of their CPU, tiny tasks have
> > > the
> > > - * ability to cross the overutilized threshold, which will
> > > - * result in the load balancer ruining all the task
> > > placement
> > > - * done by EAS. As a way to mitigate that effect, do not
> > > account
> > > - * for the first enqueue operation of new tasks during the
> > > - * overutilized flag detection.
> > > - *
> > > - * A better way of solving this problem would be to wait for
> > > - * the PELT signals of tasks to converge before taking them
> > > - * into account, but that is not straightforward to
> > > implement,
> > > - * and the following generally works well enough in
> > > practice.
> > > - */
> > > - if (flags & ENQUEUE_WAKEUP)
> > > - update_overutilized_status(rq);
> > > + /* At this point se is NULL and we are at root level*/
> > > + add_nr_running(rq, 1);
> > > +
> > > + /*
> > > + * Since new tasks are assigned an initial util_avg equal to
> > > + * half of the spare capacity of their CPU, tiny tasks have the
> > > + * ability to cross the overutilized threshold, which will
> > > + * result in the load balancer ruining all the task placement
> > > + * done by EAS. As a way to mitigate that effect, do not account
> > > + * for the first enqueue operation of new tasks during the
> > > + * overutilized flag detection.
> > > + *
> > > + * A better way of solving this problem would be to wait for
> > > + * the PELT signals of tasks to converge before taking them
> > > + * into account, but that is not straightforward to implement,
> > > + * and the following generally works well enough in practice.
> > > + */
> > > + if (flags & ENQUEUE_WAKEUP)
> > > + update_overutilized_status(rq);
> > >
> > > }
> > >
> > > +enqueue_throttle:
> > > if (cfs_bandwidth_used()) {
> > > /*
> > >* When bandwidth control is enabled; the cfs_rq_throttled()
> > > --
> > > 2.17.1
> > >
> >
> > --
> >
>
--
Re: [PATCH v2] sched/fair: enqueue_task_fair optimization
On Wed, 13 May 2020 at 14:45, Phil Auld wrote:
>
> Hi Vincent,
>
> On Wed, May 13, 2020 at 02:33:35PM +0200 Vincent Guittot wrote:
> > enqueue_task_fair jumps to enqueue_throttle label when cfs_rq_of(se) is
> > throttled which means that se can't be NULL and we can skip the test.
> >
>
> s/be NULL/be non-NULL/
>
> I think.
This sentence refers to the move of enqueue_throttle and the fact that
se can't be null when goto enqueue_throttle and we can jump directly
after the if statement, which is now removed in v2 because se is
always NULL if we don't use goto enqueue_throttle.
I haven't change the commit message for the remove of if statement
>
> It's more like if it doesn't jump to the label then se must be NULL for
> the loop to terminate. The final loop is a NOP if se is NULL. The check
> wasn't protecting that.
>
> Otherwise still
>
> > Reviewed-by: Phil Auld
>
> Cheers,
> Phil
>
>
> > Signed-off-by: Vincent Guittot
> > ---
> >
> > v2 changes:
> > - Remove useless if statement
> >
> > kernel/sched/fair.c | 39 ---
> > 1 file changed, 20 insertions(+), 19 deletions(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index a0c690d57430..b51b12d63c39 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -5513,28 +5513,29 @@ enqueue_task_fair(struct rq *rq, struct task_struct
> > *p, int flags)
> > list_add_leaf_cfs_rq(cfs_rq);
> > }
> >
> > -enqueue_throttle:
> > - if (!se) {
> > - add_nr_running(rq, 1);
> > - /*
> > - * Since new tasks are assigned an initial util_avg equal to
> > - * half of the spare capacity of their CPU, tiny tasks have
> > the
> > - * ability to cross the overutilized threshold, which will
> > - * result in the load balancer ruining all the task placement
> > - * done by EAS. As a way to mitigate that effect, do not
> > account
> > - * for the first enqueue operation of new tasks during the
> > - * overutilized flag detection.
> > - *
> > - * A better way of solving this problem would be to wait for
> > - * the PELT signals of tasks to converge before taking them
> > - * into account, but that is not straightforward to implement,
> > - * and the following generally works well enough in practice.
> > - */
> > - if (flags & ENQUEUE_WAKEUP)
> > - update_overutilized_status(rq);
> > + /* At this point se is NULL and we are at root level*/
> > + add_nr_running(rq, 1);
> > +
> > + /*
> > + * Since new tasks are assigned an initial util_avg equal to
> > + * half of the spare capacity of their CPU, tiny tasks have the
> > + * ability to cross the overutilized threshold, which will
> > + * result in the load balancer ruining all the task placement
> > + * done by EAS. As a way to mitigate that effect, do not account
> > + * for the first enqueue operation of new tasks during the
> > + * overutilized flag detection.
> > + *
> > + * A better way of solving this problem would be to wait for
> > + * the PELT signals of tasks to converge before taking them
> > + * into account, but that is not straightforward to implement,
> > + * and the following generally works well enough in practice.
> > + */
> > + if (flags & ENQUEUE_WAKEUP)
> > + update_overutilized_status(rq);
> >
> > }
> >
> > +enqueue_throttle:
> > if (cfs_bandwidth_used()) {
> > /*
> >* When bandwidth control is enabled; the cfs_rq_throttled()
> > --
> > 2.17.1
> >
>
> --
>
Re: [PATCH v2] sched/fair: enqueue_task_fair optimization
Hi Vincent,
On Wed, May 13, 2020 at 02:33:35PM +0200 Vincent Guittot wrote:
> enqueue_task_fair jumps to enqueue_throttle label when cfs_rq_of(se) is
> throttled which means that se can't be NULL and we can skip the test.
>
s/be NULL/be non-NULL/
I think.
It's more like if it doesn't jump to the label then se must be NULL for
the loop to terminate. The final loop is a NOP if se is NULL. The check
wasn't protecting that.
Otherwise still
> Reviewed-by: Phil Auld
Cheers,
Phil
> Signed-off-by: Vincent Guittot
> ---
>
> v2 changes:
> - Remove useless if statement
>
> kernel/sched/fair.c | 39 ---
> 1 file changed, 20 insertions(+), 19 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index a0c690d57430..b51b12d63c39 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5513,28 +5513,29 @@ enqueue_task_fair(struct rq *rq, struct task_struct
> *p, int flags)
> list_add_leaf_cfs_rq(cfs_rq);
> }
>
> -enqueue_throttle:
> - if (!se) {
> - add_nr_running(rq, 1);
> - /*
> - * Since new tasks are assigned an initial util_avg equal to
> - * half of the spare capacity of their CPU, tiny tasks have the
> - * ability to cross the overutilized threshold, which will
> - * result in the load balancer ruining all the task placement
> - * done by EAS. As a way to mitigate that effect, do not account
> - * for the first enqueue operation of new tasks during the
> - * overutilized flag detection.
> - *
> - * A better way of solving this problem would be to wait for
> - * the PELT signals of tasks to converge before taking them
> - * into account, but that is not straightforward to implement,
> - * and the following generally works well enough in practice.
> - */
> - if (flags & ENQUEUE_WAKEUP)
> - update_overutilized_status(rq);
> + /* At this point se is NULL and we are at root level*/
> + add_nr_running(rq, 1);
> +
> + /*
> + * Since new tasks are assigned an initial util_avg equal to
> + * half of the spare capacity of their CPU, tiny tasks have the
> + * ability to cross the overutilized threshold, which will
> + * result in the load balancer ruining all the task placement
> + * done by EAS. As a way to mitigate that effect, do not account
> + * for the first enqueue operation of new tasks during the
> + * overutilized flag detection.
> + *
> + * A better way of solving this problem would be to wait for
> + * the PELT signals of tasks to converge before taking them
> + * into account, but that is not straightforward to implement,
> + * and the following generally works well enough in practice.
> + */
> + if (flags & ENQUEUE_WAKEUP)
> + update_overutilized_status(rq);
>
> }
>
> +enqueue_throttle:
> if (cfs_bandwidth_used()) {
> /*
>* When bandwidth control is enabled; the cfs_rq_throttled()
> --
> 2.17.1
>
--
[PATCH v2] sched/fair: enqueue_task_fair optimization
enqueue_task_fair jumps to enqueue_throttle label when cfs_rq_of(se) is
throttled which means that se can't be NULL and we can skip the test.
Reviewed-by: Phil Auld
Signed-off-by: Vincent Guittot
---
v2 changes:
- Remove useless if statement
kernel/sched/fair.c | 39 ---
1 file changed, 20 insertions(+), 19 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a0c690d57430..b51b12d63c39 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5513,28 +5513,29 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p,
int flags)
list_add_leaf_cfs_rq(cfs_rq);
}
-enqueue_throttle:
- if (!se) {
- add_nr_running(rq, 1);
- /*
-* Since new tasks are assigned an initial util_avg equal to
-* half of the spare capacity of their CPU, tiny tasks have the
-* ability to cross the overutilized threshold, which will
-* result in the load balancer ruining all the task placement
-* done by EAS. As a way to mitigate that effect, do not account
-* for the first enqueue operation of new tasks during the
-* overutilized flag detection.
-*
-* A better way of solving this problem would be to wait for
-* the PELT signals of tasks to converge before taking them
-* into account, but that is not straightforward to implement,
-* and the following generally works well enough in practice.
-*/
- if (flags & ENQUEUE_WAKEUP)
- update_overutilized_status(rq);
+ /* At this point se is NULL and we are at root level*/
+ add_nr_running(rq, 1);
+
+ /*
+* Since new tasks are assigned an initial util_avg equal to
+* half of the spare capacity of their CPU, tiny tasks have the
+* ability to cross the overutilized threshold, which will
+* result in the load balancer ruining all the task placement
+* done by EAS. As a way to mitigate that effect, do not account
+* for the first enqueue operation of new tasks during the
+* overutilized flag detection.
+*
+* A better way of solving this problem would be to wait for
+* the PELT signals of tasks to converge before taking them
+* into account, but that is not straightforward to implement,
+* and the following generally works well enough in practice.
+*/
+ if (flags & ENQUEUE_WAKEUP)
+ update_overutilized_status(rq);
}
+enqueue_throttle:
if (cfs_bandwidth_used()) {
/*
* When bandwidth control is enabled; the cfs_rq_throttled()
--
2.17.1
