From: Vincent Guittot <vincent.guittot@linaro.org>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Phil Auld <pauld@redhat.com>,
Valentin Schneider <valentin.schneider@arm.com>,
Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
Quentin Perret <quentin.perret@arm.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Morten Rasmussen <Morten.Rasmussen@arm.com>,
Hillf Danton <hdanton@sina.com>, Parth Shah <parth@linux.ibm.com>,
Rik van Riel <riel@surriel.com>
Subject: Re: [PATCH v4 01/11] sched/fair: clean up asym packing
Date: Wed, 30 Oct 2019 17:03:24 +0100 [thread overview]
Message-ID: <CAKfTPtDVcHpaXTVEfTU_0A=AKXiwRD5K1eVyC43DKSF49JFWAA@mail.gmail.com> (raw)
In-Reply-To: <20191030145133.GH3016@techsingularity.net>
On Wed, 30 Oct 2019 at 15:51, Mel Gorman <mgorman@techsingularity.net> wrote:
>
> On Fri, Oct 18, 2019 at 03:26:28PM +0200, Vincent Guittot wrote:
> > Clean up asym packing to follow the default load balance behavior:
> > - classify the group by creating a group_asym_packing field.
> > - calculate the imbalance in calculate_imbalance() instead of bypassing it.
> >
> > We don't need to test twice same conditions anymore to detect asym packing
> > and we consolidate the calculation of imbalance in calculate_imbalance().
> >
> > There is no functional changes.
> >
> > Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
> > Acked-by: Rik van Riel <riel@surriel.com>
> > ---
> > kernel/sched/fair.c | 63 ++++++++++++++---------------------------------------
> > 1 file changed, 16 insertions(+), 47 deletions(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 1f0a5e1..617145c 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -7675,6 +7675,7 @@ struct sg_lb_stats {
> > unsigned int group_weight;
> > enum group_type group_type;
> > int group_no_capacity;
> > + unsigned int group_asym_packing; /* Tasks should be moved to preferred CPU */
> > unsigned long group_misfit_task_load; /* A CPU has a task too big for its capacity */
> > #ifdef CONFIG_NUMA_BALANCING
> > unsigned int nr_numa_running;
> > @@ -8129,9 +8130,17 @@ static bool update_sd_pick_busiest(struct lb_env *env,
> > * ASYM_PACKING needs to move all the work to the highest
> > * prority CPUs in the group, therefore mark all groups
> > * of lower priority than ourself as busy.
> > + *
> > + * This is primarily intended to used at the sibling level. Some
> > + * cores like POWER7 prefer to use lower numbered SMT threads. In the
> > + * case of POWER7, it can move to lower SMT modes only when higher
> > + * threads are idle. When in lower SMT modes, the threads will
> > + * perform better since they share less core resources. Hence when we
> > + * have idle threads, we want them to be the higher ones.
> > */
> > if (sgs->sum_nr_running &&
> > sched_asym_prefer(env->dst_cpu, sg->asym_prefer_cpu)) {
> > + sgs->group_asym_packing = 1;
> > if (!sds->busiest)
> > return true;
> >
>
> (I did not read any of the earlier implementations of this series, maybe
> this was discussed already in which case, sorry for the noise)
>
> Are you *sure* this is not a functional change?
>
> Asym packing is a twisty maze of headaches and I'm not familiar enough
> with it to be 100% certain without spending a lot of time on this. Even
> spotting how Power7 ends up using asym packing with lower-numbered SMT
> threads is a bit of a challenge. Specifically, it relies on the scheduler
> domain SD_ASYM_PACKING flag for SMT domains to use the weak implementation
> of arch_asym_cpu_priority which by defaults favours the lower-numbered CPU.
>
> The check_asym_packing implementation checks that flag but I can't see
> the equiavlent type of check here. update_sd_pick_busiest could be called
The checks of SD_ASYM_PACKING and CPU_NOT_IDLE are already above in
the function but out of the patch.
In fact this part of update_sd_pick_busiest is already dedicated to
asym_packing.
What I'm doing is that instead of checking asym_packing in
update_sd_pick_busiest and then rechecking the same thing in
find_busiest_group, I save the check result and reuse it
Also patch 04 moves further this code
> for domains that span NUMA or basically any domain that does not specify
> SD_ASYM_PACKING and end up favouring a lower-numbered CPU (or whatever
> arch_asym_cpu_priority returns in the case of x86 which has a different
> idea for favoured CPUs).
>
> sched_asym_prefer appears to be a function that is very easy to use
> incorrectly. Should it take env and check the SD flags first?
>
> --
> Mel Gorman
> SUSE Labs
next prev parent reply other threads:[~2019-10-30 16:03 UTC|newest]
Thread overview: 89+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-18 13:26 [PATCH v4 00/10] sched/fair: rework the CFS load balance Vincent Guittot
2019-10-18 13:26 ` [PATCH v4 01/11] sched/fair: clean up asym packing Vincent Guittot
2019-10-21 9:12 ` [tip: sched/core] sched/fair: Clean " tip-bot2 for Vincent Guittot
2019-10-30 14:51 ` [PATCH v4 01/11] sched/fair: clean " Mel Gorman
2019-10-30 16:03 ` Vincent Guittot [this message]
2019-10-18 13:26 ` [PATCH v4 02/11] sched/fair: rename sum_nr_running to sum_h_nr_running Vincent Guittot
2019-10-21 9:12 ` [tip: sched/core] sched/fair: Rename sg_lb_stats::sum_nr_running " tip-bot2 for Vincent Guittot
2019-10-30 14:53 ` [PATCH v4 02/11] sched/fair: rename sum_nr_running " Mel Gorman
2019-10-18 13:26 ` [PATCH v4 03/11] sched/fair: remove meaningless imbalance calculation Vincent Guittot
2019-10-21 9:12 ` [tip: sched/core] sched/fair: Remove " tip-bot2 for Vincent Guittot
2019-10-18 13:26 ` [PATCH v4 04/11] sched/fair: rework load_balance Vincent Guittot
2019-10-21 9:12 ` [tip: sched/core] sched/fair: Rework load_balance() tip-bot2 for Vincent Guittot
2019-10-30 15:45 ` [PATCH v4 04/11] sched/fair: rework load_balance Mel Gorman
2019-10-30 16:16 ` Valentin Schneider
2019-10-31 9:09 ` Vincent Guittot
2019-10-31 10:15 ` Mel Gorman
2019-10-31 11:13 ` Vincent Guittot
2019-10-31 11:40 ` Mel Gorman
2019-11-08 16:35 ` Vincent Guittot
2019-11-08 18:37 ` Mel Gorman
2019-11-12 10:58 ` Vincent Guittot
2019-11-12 15:06 ` Mel Gorman
2019-11-12 15:40 ` Vincent Guittot
2019-11-12 17:45 ` Mel Gorman
2019-11-18 13:50 ` Ingo Molnar
2019-11-18 13:57 ` Vincent Guittot
2019-11-18 14:51 ` Mel Gorman
2019-10-18 13:26 ` [PATCH v4 05/11] sched/fair: use rq->nr_running when balancing load Vincent Guittot
2019-10-21 9:12 ` [tip: sched/core] sched/fair: Use " tip-bot2 for Vincent Guittot
2019-10-30 15:54 ` [PATCH v4 05/11] sched/fair: use " Mel Gorman
2019-10-18 13:26 ` [PATCH v4 06/11] sched/fair: use load instead of runnable load in load_balance Vincent Guittot
2019-10-21 9:12 ` [tip: sched/core] sched/fair: Use load instead of runnable load in load_balance() tip-bot2 for Vincent Guittot
2019-10-30 15:58 ` [PATCH v4 06/11] sched/fair: use load instead of runnable load in load_balance Mel Gorman
2019-10-18 13:26 ` [PATCH v4 07/11] sched/fair: evenly spread tasks when not overloaded Vincent Guittot
2019-10-21 9:12 ` [tip: sched/core] sched/fair: Spread out tasks evenly " tip-bot2 for Vincent Guittot
2019-10-30 16:03 ` [PATCH v4 07/11] sched/fair: evenly spread tasks " Mel Gorman
2019-10-18 13:26 ` [PATCH v4 08/11] sched/fair: use utilization to select misfit task Vincent Guittot
2019-10-21 9:12 ` [tip: sched/core] sched/fair: Use " tip-bot2 for Vincent Guittot
2019-10-18 13:26 ` [PATCH v4 09/11] sched/fair: use load instead of runnable load in wakeup path Vincent Guittot
2019-10-21 9:12 ` [tip: sched/core] sched/fair: Use " tip-bot2 for Vincent Guittot
2019-10-18 13:26 ` [PATCH v4 10/11] sched/fair: optimize find_idlest_group Vincent Guittot
2019-10-21 9:12 ` [tip: sched/core] sched/fair: Optimize find_idlest_group() tip-bot2 for Vincent Guittot
2019-10-18 13:26 ` [PATCH v4 11/11] sched/fair: rework find_idlest_group Vincent Guittot
2019-10-21 9:12 ` [tip: sched/core] sched/fair: Rework find_idlest_group() tip-bot2 for Vincent Guittot
2019-10-22 16:46 ` [PATCH] sched/fair: fix rework of find_idlest_group() Vincent Guittot
2019-10-23 7:50 ` Chen, Rong A
2019-10-30 16:07 ` Mel Gorman
2019-11-18 17:42 ` [tip: sched/core] sched/fair: Fix " tip-bot2 for Vincent Guittot
2019-11-22 14:37 ` [PATCH] sched/fair: fix " Valentin Schneider
2019-11-25 9:16 ` Vincent Guittot
2019-11-25 11:03 ` Valentin Schneider
2019-11-20 11:58 ` [PATCH v4 11/11] sched/fair: rework find_idlest_group Qais Yousef
2019-11-20 13:21 ` Vincent Guittot
2019-11-20 16:53 ` Vincent Guittot
2019-11-20 17:34 ` Qais Yousef
2019-11-20 17:43 ` Vincent Guittot
2019-11-20 18:10 ` Qais Yousef
2019-11-20 18:20 ` Vincent Guittot
2019-11-20 18:27 ` Qais Yousef
2019-11-20 19:28 ` Vincent Guittot
2019-11-20 19:55 ` Qais Yousef
2019-11-21 14:58 ` Qais Yousef
2019-11-22 14:34 ` Valentin Schneider
2019-11-25 9:59 ` Vincent Guittot
2019-11-25 11:13 ` Valentin Schneider
2019-10-21 7:50 ` [PATCH v4 00/10] sched/fair: rework the CFS load balance Ingo Molnar
2019-10-21 8:44 ` Vincent Guittot
2019-10-21 12:56 ` Phil Auld
2019-10-24 12:38 ` Phil Auld
2019-10-24 13:46 ` Phil Auld
2019-10-24 14:59 ` Vincent Guittot
2019-10-25 13:33 ` Phil Auld
2019-10-28 13:03 ` Vincent Guittot
2019-10-30 14:39 ` Phil Auld
2019-10-30 16:24 ` Dietmar Eggemann
2019-10-30 16:35 ` Valentin Schneider
2019-10-30 17:19 ` Phil Auld
2019-10-30 17:25 ` Valentin Schneider
2019-10-30 17:29 ` Phil Auld
2019-10-30 17:28 ` Vincent Guittot
2019-10-30 17:44 ` Phil Auld
2019-10-30 17:25 ` Vincent Guittot
2019-10-31 13:57 ` Phil Auld
2019-10-31 16:41 ` Vincent Guittot
2019-10-30 16:24 ` Mel Gorman
2019-10-30 16:35 ` Vincent Guittot
2019-11-18 13:15 ` Ingo Molnar
2019-11-25 12:48 ` Valentin Schneider
2020-01-03 16:39 ` Valentin Schneider
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