Messages in this thread Patch in this message | | | Subject | Re: [PATCH v3 04/10] sched/fair: Let low-priority cores help high-priority busy SMT cores | From | Tim Chen <> | Date | Thu, 09 Mar 2023 16:51:35 -0800 |
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On Mon, 2023-02-06 at 20:58 -0800, Ricardo Neri wrote: > Using asym_packing priorities within an SMT core is straightforward. > Just > follow the priorities that hardware indicates. > > When balancing load from an SMT core, also consider the idle of its > siblings. Priorities do not reflect that an SMT core divides its > throughput > among all its busy siblings. They only makes sense when exactly one > sibling > is busy. > > Indicate that active balance is needed if the destination CPU has > lower > priority than the source CPU but the latter has busy SMT siblings. > > Make find_busiest_queue() not skip higher-priority SMT cores with > more than > busy sibling. > > Cc: Ben Segall <bsegall@google.com> > Cc: Daniel Bristot de Oliveira <bristot@redhat.com> > Cc: Dietmar Eggemann <dietmar.eggemann@arm.com> > Cc: Len Brown <len.brown@intel.com> > Cc: Mel Gorman <mgorman@suse.de> > 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 C. Chen <tim.c.chen@intel.com> > Cc: Valentin Schneider <vschneid@redhat.com> > Cc: x86@kernel.org > Cc: linux-kernel@vger.kernel.org > Suggested-by: Valentin Schneider <vschneid@redhat.com> > Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com> > --- > Changes since v2: > * Introduced this patch. > > Changes since v1: > * N/A > --- > kernel/sched/fair.c | 31 ++++++++++++++++++++++++++----- > 1 file changed, 26 insertions(+), 5 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 80c86462c6f6..c9d0ddfd11f2 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -10436,11 +10436,20 @@ 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 */ > + /* > + * Make sure we only pull tasks from a CPU of lower > priority > + * when balancing between SMT siblings. > + * > + * If balancing between cores, let lower priority > CPUs help > + * SMT cores with more than one busy sibling. > + */ > if ((env->sd->flags & SD_ASYM_PACKING) && > sched_asym_prefer(i, env->dst_cpu) && > - nr_running == 1) > - continue; > + nr_running == 1) { > + if (env->sd->flags & SD_SHARE_CPUCAPACITY || > + (!(env->sd->flags & SD_SHARE_CPUCAPACITY) > && is_core_idle(i))) > + continue; > + } > > switch (env->migration_type) { > case migrate_load: > @@ -10530,8 +10539,20 @@ asym_active_balance(struct lb_env *env) > * lower priority CPUs in order to pack all tasks in the > * highest priority CPUs. > */ > - return env->idle != CPU_NOT_IDLE && (env->sd->flags & > SD_ASYM_PACKING) && > - sched_asym_prefer(env->dst_cpu, env->src_cpu); > + if (env->idle != CPU_NOT_IDLE && (env->sd->flags & > SD_ASYM_PACKING)) { > + /* Always obey priorities between SMT siblings. */ > + if (env->sd->flags & SD_SHARE_CPUCAPACITY) > + return sched_asym_prefer(env->dst_cpu, env- > >src_cpu); > + > + /* > + * A lower priority CPU can help an SMT core with > more than one > + * busy sibling. > + */ > + return sched_asym_prefer(env->dst_cpu, env->src_cpu) > || > + !is_core_idle(env->src_cpu); > + }
Suppose we have the Atom cores in a sched group (e.g. a cluster), this will pull the tasks from those core to a SMT thread even if its sibling thread is busy. Suggest this change
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index da1afa99cd55..b671cb0d7ab3 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -10473,9 +10473,11 @@ asym_active_balance(struct lb_env *env) /* * A lower priority CPU can help an SMT core with more than one * busy sibling. + * Pull only if no SMT sibling busy. */ - return sched_asym_prefer(env->dst_cpu, env->src_cpu) || - !is_core_idle(env->src_cpu); + if (is_core_idle(env->dst_cpu)) + return sched_asym_prefer(env->dst_cpu, env->src_cpu) || + !is_core_idle(env->src_cpu); }
Tim > + > + return false; > } > > static inline bool
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