Messages in this thread Patch in this message | | | Subject | Re: [PATCH v5 6/6] sched/fair: Consider SMT in ASYM_PACKING load balance | From | Guillaume Tucker <> | Date | Fri, 1 Oct 2021 11:33:34 +0200 |
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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
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* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 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@kernelci.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@linux.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@intel.com> > Cc: Ben Segall <bsegall@google.com> > Cc: Daniel Bristot de Oliveira <bristot@redhat.com> > Cc: Dietmar Eggemann <dietmar.eggemann@arm.com> > Cc: Mel Gorman <mgorman@suse.de> > Cc: Quentin Perret <qperret@google.com> > Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com> > Cc: Steven Rostedt <rostedt@goodmis.org> > Cc: Tim Chen <tim.c.chen@linux.intel.com> > Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org> > Reviewed-by: Len Brown <len.brown@intel.com> > Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.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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