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Message-ID: <78608a82-93b8-8036-2bf0-65f53f2f5120@collabora.com>
Date: Fri, 1 Oct 2021 11:33:34 +0200
From: Guillaume Tucker <guillaume.tucker@...labora.com>
To: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>
Cc: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
Nicholas Piggin <npiggin@...il.com>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
Len Brown <len.brown@...el.com>,
Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Aubrey Li <aubrey.li@...ux.intel.com>,
"Ravi V. Shankar" <ravi.v.shankar@...el.com>,
Ricardo Neri <ricardo.neri@...el.com>,
Quentin Perret <qperret@...gle.com>,
"Joel Fernandes (Google)" <joel@...lfernandes.org>,
linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
Aubrey Li <aubrey.li@...el.com>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
"kernelci-results@...ups.io" <kernelci-results@...ups.io>
Subject: Re: [PATCH v5 6/6] sched/fair: Consider SMT in ASYM_PACKING load
balance
Hi Ricardo,
Please see the bisection report below about a boot failure on
rk3288-rock64.
Reports aren't automatically sent to the public while we're
trialing new bisection features on kernelci.org but this one
looks valid.
Some more details can be found here:
https://linux.kernelci.org/test/case/id/6155a4b0836c79a98f99a31d/
It looks like some i.MX arm64 platforms also regressed with
next-20210920 although it hasn't been verified yet whether that's
due to the same commit:
https://linux.kernelci.org/test/job/next/branch/master/kernel/next-20210930/plan/baseline/
The x86 platforms don't seem to be impacted though.
Please let us know if you need help debugging the issue or if you
have a fix to try.
Best wishes,
Guillaume
GitHub: https://github.com/kernelci/kernelci-project/issues/65
-------------------------------------------------------------------------------
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* This automated bisection report was sent to you on the basis *
* that you may be involved with the breaking commit it has *
* found. No manual investigation has been done to verify it, *
* and the root cause of the problem may be somewhere else. *
* *
* If you do send a fix, please include this trailer: *
* Reported-by: "kernelci.org bot" <bot@...nelci.org> *
* *
* Hope this helps! *
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
next/master bisection: baseline.login on rk3328-rock64
Summary:
Start: 2d02a18f75fc Add linux-next specific files for 20210929
Plain log: https://storage.kernelci.org/next/master/next-20210929/arm64/defconfig+CONFIG_RANDOMIZE_BASE=y/gcc-8/lab-baylibre/baseline-rk3328-rock64.txt
HTML log: https://storage.kernelci.org/next/master/next-20210929/arm64/defconfig+CONFIG_RANDOMIZE_BASE=y/gcc-8/lab-baylibre/baseline-rk3328-rock64.html
Result: eac6f3841f1d sched/fair: Consider SMT in ASYM_PACKING load balance
Checks:
revert: PASS
verify: PASS
Parameters:
Tree: next
URL: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
Branch: master
Target: rk3328-rock64
CPU arch: arm64
Lab: lab-baylibre
Compiler: gcc-8
Config: defconfig+CONFIG_RANDOMIZE_BASE=y
Test case: baseline.login
Breaking commit found:
-------------------------------------------------------------------------------
commit eac6f3841f1dac7b6f43002056b63f44cc1f1543
Author: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Date: Fri Sep 10 18:18:19 2021 -0700
sched/fair: Consider SMT in ASYM_PACKING load balance
On 11/09/2021 03:18, Ricardo Neri wrote:
> When deciding to pull tasks in ASYM_PACKING, it is necessary not only to
> check for the idle state of the destination CPU, dst_cpu, but also of
> its SMT siblings.
>
> If dst_cpu is idle but its SMT siblings are busy, performance suffers
> if it pulls tasks from a medium priority CPU that does not have SMT
> siblings.
>
> Implement asym_smt_can_pull_tasks() to inspect the state of the SMT
> siblings of both dst_cpu and the CPUs in the candidate busiest group.
>
> Cc: Aubrey Li <aubrey.li@...el.com>
> Cc: Ben Segall <bsegall@...gle.com>
> Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
> Cc: Dietmar Eggemann <dietmar.eggemann@....com>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Quentin Perret <qperret@...gle.com>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Cc: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Tim Chen <tim.c.chen@...ux.intel.com>
> Reviewed-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> Reviewed-by: Len Brown <len.brown@...el.com>
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
> ---
> Changes since v4:
> * Use sg_lb_stats::sum_nr_running the idle state of a scheduling group.
> (Vincent, Peter)
> * Do not even idle CPUs in asym_smt_can_pull_tasks(). (Vincent)
> * Updated function documentation and corrected a typo.
>
> Changes since v3:
> * Removed the arch_asym_check_smt_siblings() hook. Discussions with the
> powerpc folks showed that this patch should not impact them. Also, more
> recent powerpc processor no longer use asym_packing. (PeterZ)
> * Removed unnecessary local variable in asym_can_pull_tasks(). (Dietmar)
> * Removed unnecessary check for local CPUs when the local group has zero
> utilization. (Joel)
> * Renamed asym_can_pull_tasks() as asym_smt_can_pull_tasks() to reflect
> the fact that it deals with SMT cases.
> * Made asym_smt_can_pull_tasks() return false for !CONFIG_SCHED_SMT so
> that callers can deal with non-SMT cases.
>
> Changes since v2:
> * Reworded the commit message to reflect updates in code.
> * Corrected misrepresentation of dst_cpu as the CPU doing the load
> balancing. (PeterZ)
> * Removed call to arch_asym_check_smt_siblings() as it is now called in
> sched_asym().
>
> Changes since v1:
> * Don't bailout in update_sd_pick_busiest() if dst_cpu cannot pull
> tasks. Instead, reclassify the candidate busiest group, as it
> may still be selected. (PeterZ)
> * Avoid an expensive and unnecessary call to cpumask_weight() when
> determining if a sched_group is comprised of SMT siblings.
> (PeterZ).
> ---
> kernel/sched/fair.c | 94 +++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 94 insertions(+)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 26db017c14a3..8d763dd0174b 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -8597,10 +8597,98 @@ group_type group_classify(unsigned int imbalance_pct,
> return group_has_spare;
> }
>
> +/**
> + * asym_smt_can_pull_tasks - Check whether the load balancing CPU can pull tasks
> + * @dst_cpu: Destination CPU of the load balancing
> + * @sds: Load-balancing data with statistics of the local group
> + * @sgs: Load-balancing statistics of the candidate busiest group
> + * @sg: The candidate busiest group
> + *
> + * Check the state of the SMT siblings of both @sds::local and @sg and decide
> + * if @dst_cpu can pull tasks.
> + *
> + * If @dst_cpu does not have SMT siblings, it can pull tasks if two or more of
> + * the SMT siblings of @sg are busy. If only one CPU in @sg is busy, pull tasks
> + * only if @dst_cpu has higher priority.
> + *
> + * If both @dst_cpu and @sg have SMT siblings, and @sg has exactly one more
> + * busy CPU than @sds::local, let @dst_cpu pull tasks if it has higher priority.
> + * Bigger imbalances in the number of busy CPUs will be dealt with in
> + * update_sd_pick_busiest().
> + *
> + * If @sg does not have SMT siblings, only pull tasks if all of the SMT siblings
> + * of @dst_cpu are idle and @sg has lower priority.
> + */
> +static bool asym_smt_can_pull_tasks(int dst_cpu, struct sd_lb_stats *sds,
> + struct sg_lb_stats *sgs,
> + struct sched_group *sg)
> +{
> +#ifdef CONFIG_SCHED_SMT
> + bool local_is_smt, sg_is_smt;
> + int sg_busy_cpus;
> +
> + local_is_smt = sds->local->flags & SD_SHARE_CPUCAPACITY;
> + sg_is_smt = sg->flags & SD_SHARE_CPUCAPACITY;
> +
> + sg_busy_cpus = sgs->group_weight - sgs->idle_cpus;
> +
> + if (!local_is_smt) {
> + /*
> + * If we are here, @dst_cpu is idle and does not have SMT
> + * siblings. Pull tasks if candidate group has two or more
> + * busy CPUs.
> + */
> + if (sg_is_smt && sg_busy_cpus >= 2)
> + return true;
> +
> + /*
> + * @dst_cpu does not have SMT siblings. @sg may have SMT
> + * siblings and only one is busy. In such case, @dst_cpu
> + * can help if it has higher priority and is idle (i.e.,
> + * it has no running tasks).
> + */
> + return !sds->local_stat.sum_nr_running &&
> + sched_asym_prefer(dst_cpu, sg->asym_prefer_cpu);
> + }
> +
> + /* @dst_cpu has SMT siblings. */
> +
> + if (sg_is_smt) {
> + int local_busy_cpus = sds->local->group_weight -
> + sds->local_stat.idle_cpus;
> + int busy_cpus_delta = sg_busy_cpus - local_busy_cpus;
> +
> + if (busy_cpus_delta == 1)
> + return sched_asym_prefer(dst_cpu,
> + sg->asym_prefer_cpu);
> +
> + return false;
> + }
> +
> + /*
> + * @sg does not have SMT siblings. Ensure that @sds::local does not end
> + * up with more than one busy SMT sibling and only pull tasks if there
> + * are not busy CPUs (i.e., no CPU has running tasks).
> + */
> + if (!sds->local_stat.sum_nr_running)
> + return sched_asym_prefer(dst_cpu, sg->asym_prefer_cpu);
> +
> + return false;
> +#else
> + /* Always return false so that callers deal with non-SMT cases. */
> + return false;
> +#endif
> +}
> +
> static inline bool
> sched_asym(struct lb_env *env, struct sd_lb_stats *sds, struct sg_lb_stats *sgs,
> struct sched_group *group)
> {
> + /* Only do SMT checks if either local or candidate have SMT siblings */
> + if ((sds->local->flags & SD_SHARE_CPUCAPACITY) ||
> + (group->flags & SD_SHARE_CPUCAPACITY))
> + return asym_smt_can_pull_tasks(env->dst_cpu, sds, sgs, group);
> +
> return sched_asym_prefer(env->dst_cpu, group->asym_prefer_cpu);
> }
>
> @@ -9606,6 +9694,12 @@ static struct rq *find_busiest_queue(struct lb_env *env,
> nr_running == 1)
> continue;
>
> + /* Make sure we only pull tasks from a CPU of lower priority */
> + if ((env->sd->flags & SD_ASYM_PACKING) &&
> + sched_asym_prefer(i, env->dst_cpu) &&
> + nr_running == 1)
> + continue;
> +
> switch (env->migration_type) {
> case migrate_load:
> /*
>
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