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Message-ID: <CAKfTPtB_YR8e6fcx3Un0vTeJR4EJS9sOXG=wLb8rZeM5Ub4yyA@mail.gmail.com>
Date: Wed, 8 Feb 2023 08:56:32 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>,
Ricardo Neri <ricardo.neri@...el.com>,
"Ravi V. Shankar" <ravi.v.shankar@...el.com>,
Ben Segall <bsegall@...gle.com>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Len Brown <len.brown@...el.com>, Mel Gorman <mgorman@...e.de>,
"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
Steven Rostedt <rostedt@...dmis.org>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Valentin Schneider <vschneid@...hat.com>,
Ionela Voinescu <ionela.voinescu@....com>, x86@...nel.org,
linux-kernel@...r.kernel.org, "Tim C . Chen" <tim.c.chen@...el.com>
Subject: Re: [PATCH v3 04/10] sched/fair: Let low-priority cores help
high-priority busy SMT cores
On Tue, 7 Feb 2023 at 05:50, Ricardo Neri
<ricardo.neri-calderon@...ux.intel.com> 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@...gle.com>
> Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
> Cc: Dietmar Eggemann <dietmar.eggemann@....com>
> Cc: Len Brown <len.brown@...el.com>
> Cc: Mel Gorman <mgorman@...e.de>
> 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 C. Chen <tim.c.chen@...el.com>
> Cc: Valentin Schneider <vschneid@...hat.com>
> Cc: x86@...nel.org
> Cc: linux-kernel@...r.kernel.org
> Suggested-by: Valentin Schneider <vschneid@...hat.com>
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.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)))
This 2nd if could be merged with the upper one
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10518,11 +10518,10 @@ static struct rq *find_busiest_queue(struct
lb_env *env,
*/
if ((env->sd->flags & SD_ASYM_PACKING) &&
sched_asym_prefer(i, env->dst_cpu) &&
- nr_running == 1) {
- if (env->sd->flags & SD_SHARE_CPUCAPACITY ||
- (!(env->sd->flags & SD_SHARE_CPUCAPACITY)
&& is_core_idle(i)))
+ (nr_running == 1) &&
+ (env->sd->flags & SD_SHARE_CPUCAPACITY ||
+ (!(env->sd->flags & SD_SHARE_CPUCAPACITY)
&& is_core_idle(i))))
continue;
- }
switch (env->migration_type) {
case migrate_load:
---
AFAICT, you can even remove one env->sd->flags & SD_SHARE_CPUCAPACITY
test with the below but this make the condition far less obvious
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a6021af9de11..7dfa30c45327 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10518,11 +10518,10 @@ static struct rq *find_busiest_queue(struct
lb_env *env,
*/
if ((env->sd->flags & SD_ASYM_PACKING) &&
sched_asym_prefer(i, env->dst_cpu) &&
- nr_running == 1) {
- if (env->sd->flags & SD_SHARE_CPUCAPACITY ||
- (!(env->sd->flags & SD_SHARE_CPUCAPACITY)
&& is_core_idle(i)))
+ (nr_running == 1) &&
+ !(!(env->sd->flags & SD_SHARE_CPUCAPACITY) &&
+ !is_core_idle(i)))
continue;
- }
> + 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);
> + }
> +
> + return false;
> }
>
> static inline bool
> --
> 2.25.1
>
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