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sched/fair: Clean up asym packing 

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>
Cc: Ben Segall <bsegall@google.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Morten.Rasmussen@arm.com
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: hdanton@sina.com
Cc: parth@linux.ibm.com
Cc: pauld@redhat.com
Cc: quentin.perret@arm.com
Cc: srikar@linux.vnet.ibm.com
Cc: valentin.schneider@arm.com
Link: https://lkml.kernel.org/r/1571405198-27570-2-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Vincent Guittot 2019-10-18 15:26:28 +02:00 committed by Ingo Molnar
parent 9ae7ab20b4
commit 490ba971d8
1 changed files with 16 additions and 47 deletions
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63
kernel/sched/fair.c
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@ -7665,6 +7665,7 @@ 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;
@ -8119,9 +8120,17 @@ asym_packing:
* 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;
@ -8262,51 +8271,6 @@ next_group:
}
}
/**
* check_asym_packing - Check to see if the group is packed into the
* sched domain.
*
* 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.
*
* This packing function is run on idle threads. It checks to see if
* the busiest CPU in this domain (core in the P7 case) has a higher
* CPU number than the packing function is being run on. Here we are
* assuming lower CPU number will be equivalent to lower a SMT thread
* number.
*
* Return: 1 when packing is required and a task should be moved to
* this CPU. The amount of the imbalance is returned in env->imbalance.
*
* @env: The load balancing environment.
* @sds: Statistics of the sched_domain which is to be packed
*/
static int check_asym_packing(struct lb_env *env, struct sd_lb_stats *sds)
{
int busiest_cpu;
if (!(env->sd->flags & SD_ASYM_PACKING))
return 0;
if (env->idle == CPU_NOT_IDLE)
return 0;
if (!sds->busiest)
return 0;
busiest_cpu = sds->busiest->asym_prefer_cpu;
if (sched_asym_prefer(busiest_cpu, env->dst_cpu))
return 0;
env->imbalance = sds->busiest_stat.group_load;
return 1;
}
/**
* fix_small_imbalance - Calculate the minor imbalance that exists
* amongst the groups of a sched_domain, during
@ -8391,6 +8355,11 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
local = &sds->local_stat;
busiest = &sds->busiest_stat;
if (busiest->group_asym_packing) {
env->imbalance = busiest->group_load;
return;
}
if (busiest->group_type == group_imbalanced) {
/*
* In the group_imb case we cannot rely on group-wide averages
@ -8495,8 +8464,8 @@ static struct sched_group *find_busiest_group(struct lb_env *env)
busiest = &sds.busiest_stat;
/* ASYM feature bypasses nice load balance check */
if (check_asym_packing(env, &sds))
return sds.busiest;
if (busiest->group_asym_packing)
goto force_balance;
/* There is no busy sibling group to pull tasks from */
if (!sds.busiest || busiest->sum_nr_running == 0)