Re: [PATCH 2/6] sched/fair: remove unused parameter of update_nohz_stats

[Vincent Guittot]

On Tue, 9 Feb 2021 at 14:45, Dietmar Eggemann  wrote:
>
> On 05/02/2021 12:48, Vincent Guittot wrote:
> > idle load balance is the only user of update_nohz_stats and doesn't use
> > force parameter. Remove it
>
> Wasn't the 'force=true' from ilb eclipsing the jiffy resolution rate
> limiting '!time_after(jiffies, rq->last_blocked_load_update_tick)' of
> update_blocked_averages()?
>
> So IMHO this has the (maybe intended) side effect that (formerly forced
> updates) are now rate limited on one jiffy resolution too.

Calls to _nohz_idle_balance were already rate limited by load balance
interval and nohz.next_blocked.
This tick rate limit has been originally added for newidle_balance
case but there were some corner cases for _nohz_idle_balance that
could benefit of this too

>
> >
> > Signed-off-by: Vincent Guittot 
> > ---
> >  kernel/sched/fair.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index bfe1e235fe01..60b8c1c68ab9 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -8352,7 +8352,7 @@ group_type group_classify(unsigned int imbalance_pct,
> >   return group_has_spare;
> >  }
> >
> > -static bool update_nohz_stats(struct rq *rq, bool force)
> > +static bool update_nohz_stats(struct rq *rq)
> >  {
> >  #ifdef CONFIG_NO_HZ_COMMON
> >   unsigned int cpu = rq->cpu;
> > @@ -8363,7 +8363,7 @@ static bool update_nohz_stats(struct rq *rq, bool 
> > force)
> >   if (!cpumask_test_cpu(cpu, nohz.idle_cpus_mask))
> >   return false;
> >
> > - if (!force && !time_after(jiffies, rq->last_blocked_load_update_tick))
> > + if (!time_after(jiffies, rq->last_blocked_load_update_tick))
> >   return true;
> >
> >   update_blocked_averages(cpu);
> > @@ -10404,7 +10404,7 @@ static bool _nohz_idle_balance(struct rq *this_rq, 
> > unsigned int flags,
> >
> >   rq = cpu_rq(balance_cpu);
> >
> > - has_blocked_load |= update_nohz_stats(rq, true);
> > + has_blocked_load |= update_nohz_stats(rq);
> >
> >   /*
> >* If time for next balance is due,
> >
>

Re: [PATCH 2/6] sched/fair: remove unused parameter of update_nohz_stats

[Dietmar Eggemann]

On 05/02/2021 12:48, Vincent Guittot wrote:
> idle load balance is the only user of update_nohz_stats and doesn't use
> force parameter. Remove it

Wasn't the 'force=true' from ilb eclipsing the jiffy resolution rate
limiting '!time_after(jiffies, rq->last_blocked_load_update_tick)' of
update_blocked_averages()?

So IMHO this has the (maybe intended) side effect that (formerly forced
updates) are now rate limited on one jiffy resolution too.

> 
> Signed-off-by: Vincent Guittot 
> ---
>  kernel/sched/fair.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index bfe1e235fe01..60b8c1c68ab9 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -8352,7 +8352,7 @@ group_type group_classify(unsigned int imbalance_pct,
>   return group_has_spare;
>  }
>  
> -static bool update_nohz_stats(struct rq *rq, bool force)
> +static bool update_nohz_stats(struct rq *rq)
>  {
>  #ifdef CONFIG_NO_HZ_COMMON
>   unsigned int cpu = rq->cpu;
> @@ -8363,7 +8363,7 @@ static bool update_nohz_stats(struct rq *rq, bool force)
>   if (!cpumask_test_cpu(cpu, nohz.idle_cpus_mask))
>   return false;
>  
> - if (!force && !time_after(jiffies, rq->last_blocked_load_update_tick))
> + if (!time_after(jiffies, rq->last_blocked_load_update_tick))
>   return true;
>  
>   update_blocked_averages(cpu);
> @@ -10404,7 +10404,7 @@ static bool _nohz_idle_balance(struct rq *this_rq, 
> unsigned int flags,
>  
>   rq = cpu_rq(balance_cpu);
>  
> - has_blocked_load |= update_nohz_stats(rq, true);
> + has_blocked_load |= update_nohz_stats(rq);
>  
>   /*
>* If time for next balance is due,
> 

[PATCH 2/6] sched/fair: remove unused parameter of update_nohz_stats

[Vincent Guittot]

idle load balance is the only user of update_nohz_stats and doesn't use
force parameter. Remove it

Signed-off-by: Vincent Guittot 
---
 kernel/sched/fair.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index bfe1e235fe01..60b8c1c68ab9 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8352,7 +8352,7 @@ group_type group_classify(unsigned int imbalance_pct,
return group_has_spare;
 }
 
-static bool update_nohz_stats(struct rq *rq, bool force)
+static bool update_nohz_stats(struct rq *rq)
 {
 #ifdef CONFIG_NO_HZ_COMMON
unsigned int cpu = rq->cpu;
@@ -8363,7 +8363,7 @@ static bool update_nohz_stats(struct rq *rq, bool force)
if (!cpumask_test_cpu(cpu, nohz.idle_cpus_mask))
return false;
 
-   if (!force && !time_after(jiffies, rq->last_blocked_load_update_tick))
+   if (!time_after(jiffies, rq->last_blocked_load_update_tick))
return true;
 
update_blocked_averages(cpu);
@@ -10404,7 +10404,7 @@ static bool _nohz_idle_balance(struct rq *this_rq, 
unsigned int flags,
 
rq = cpu_rq(balance_cpu);
 
-   has_blocked_load |= update_nohz_stats(rq, true);
+   has_blocked_load |= update_nohz_stats(rq);
 
/*
 * If time for next balance is due,
-- 
2.17.1