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Message-ID: <dee7575cc9d3c42c9705348151a1453ff084d4f3.camel@linux.intel.com>
Date: Tue, 05 Sep 2023 11:37:15 -0700
From: Tim Chen <tim.c.chen@...ux.intel.com>
To: Shrikanth Hegde <sshegde@...ux.vnet.ibm.com>, peterz@...radead.org
Cc: bristot@...hat.com, bsegall@...gle.com, dietmar.eggemann@....com,
hdanton@...a.com, ionela.voinescu@....com, juri.lelli@...hat.com,
len.brown@...el.com, linux-kernel@...r.kernel.org, mgorman@...e.de,
naveen.n.rao@...ux.vnet.ibm.com, rafael.j.wysocki@...el.com,
ravi.v.shankar@...el.com, ricardo.neri@...el.com,
rostedt@...dmis.org, srikar@...ux.vnet.ibm.com,
srinivas.pandruvada@...ux.intel.com, v-songbaohua@...o.com,
vincent.guittot@...aro.org, vschneid@...hat.com, x86@...nel.org,
yangyicong@...ilicon.com, yu.c.chen@...el.com
Subject: Re: [PATCH] sched/fair: Add SMT4 group_smt_balance handling
On Tue, 2023-09-05 at 13:33 +0530, Shrikanth Hegde wrote:
>
> On 8/22/23 12:49 AM, Tim Chen wrote:
> > On Mon, 2023-08-07 at 15:06 +0530, Shrikanth Hegde wrote:
> > > >
> > > > From: Tim Chen <tim.c.chen@...ux.intel.com>
> > > > Date: Fri, 14 Jul 2023 16:09:30 -0700
> > > > Subject: [PATCH] sched/fair: Add SMT4 group_smt_balance handling
> > > >
> > > > For SMT4, any group with more than 2 tasks will be marked as
> > > > group_smt_balance. Retain the behaviour of group_has_spare by marking
> > > > the busiest group as the group which has the least number of idle_cpus.
> > > >
> > > > Also, handle rounding effect of adding (ncores_local + ncores_busy)
> > > > when the local is fully idle and busy group has more than 2 tasks.
> > > > Local group should try to pull at least 1 task in this case.
> > > >
> > > > Signed-off-by: Tim Chen <tim.c.chen@...ux.intel.com>
> > > > ---
> > > > kernel/sched/fair.c | 18 ++++++++++++++++--
> > > > 1 file changed, 16 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > > > index a87988327f88..566686c5f2bd 100644
> > > > --- a/kernel/sched/fair.c
> > > > +++ b/kernel/sched/fair.c
> > > > @@ -9563,7 +9563,7 @@ static inline long sibling_imbalance(struct lb_env *env,
> > > > imbalance /= ncores_local + ncores_busiest;
> > > >
> > > > /* Take advantage of resource in an empty sched group */
> > > > - if (imbalance == 0 && local->sum_nr_running == 0 &&
> > > > + if (imbalance <= 1 && local->sum_nr_running == 0 &&
> > > > busiest->sum_nr_running > 1)
> > > > imbalance = 2;
> > > >
> > > > @@ -9751,6 +9751,20 @@ static bool update_sd_pick_busiest(struct lb_env *env,
> > > > break;
> > > >
> > > > case group_smt_balance:
> > > > + /* no idle cpus on both groups handled by group_fully_busy below */
> > > > + if (sgs->idle_cpus != 0 || busiest->idle_cpus != 0) {
> > > > + if (sgs->idle_cpus > busiest->idle_cpus)
> > > > + return false;
> > > > + if (sgs->idle_cpus < busiest->idle_cpus)
> > > > + return true;
> > > > + if (sgs->sum_nr_running <= busiest->sum_nr_running)
> > > > + return false;
> > > > + else
> > > > + return true;
> > > > + }
> > > > + goto fully_busy;
> > > > + break;
> > > > +
> > > > case group_fully_busy:
> > > > /*
> > > > * Select the fully busy group with highest avg_load. In
> > > > @@ -9763,7 +9777,7 @@ static bool update_sd_pick_busiest(struct lb_env *env,
> > > > * select the 1st one, except if @sg is composed of SMT
> > > > * siblings.
> > > > */
> > > > -
> > > > +fully_busy:
> > > > if (sgs->avg_load < busiest->avg_load)
> > > > return false;
> > > >
> > >
> > > Hi Tim, Peter.
> > >
> > > group_smt_balance(cluster scheduling), patches are in tip/sched/core. I dont
> > > see this above patch there yet. Currently as is, this can cause function difference
> > > in SMT4 systems( such as Power10).
> > >
> > > Can we please have the above patch as well in tip/sched/core?
> > >
> > > Acked-by: Shrikanth Hegde <sshegde@...ux.vnet.ibm.com>
> >
> > Hi Peter,
> >
> > Just back from my long vacation. Wonder if you have any comments on the above patch
> > for fixing the SMT4 case?
> >
> > Tim
>
> Hi Tim, Peter.
>
> are there any concerns with the above patch for fixing the SMT4 case.
> Currently the behavior is group_smt_balance is set for having even 2 tasks in
> SMT4, ideally it should be same as the group_has_spare.
>
> The above patch copies the same behavior to group_smt_balance.
> >
You mean simplify the patch as below? I think that should be fine. Can you
make sure it works for SMT4? And I can update the patch once you confirm it
works properly.
Tim
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6e7ee2efc1ba..48e9ab7f8a87 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9764,16 +9764,9 @@ static bool update_sd_pick_busiest(struct lb_env *env,
case group_smt_balance:
/* no idle cpus on both groups handled by group_fully_busy below */
- if (sgs->idle_cpus != 0 || busiest->idle_cpus != 0) {
- if (sgs->idle_cpus > busiest->idle_cpus)
- return false;
- if (sgs->idle_cpus < busiest->idle_cpus)
- return true;
- if (sgs->sum_nr_running <= busiest->sum_nr_running)
- return false;
- else
- return true;
- }
+ if (sgs->idle_cpus != 0 || busiest->idle_cpus != 0)
+ goto has_spare;
+
goto fully_busy;
case group_fully_busy:
@@ -9809,6 +9802,7 @@ static bool update_sd_pick_busiest(struct lb_env *env,
* as we do not want to pull task off SMT core with one task
* and make the core idle.
*/
+has_spare:
if (smt_vs_nonsmt_groups(sds->busiest, sg)) {
if (sg->flags & SD_SHARE_CPUCAPACITY && sgs->sum_h_nr_running <= 1)
return false;
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