Re: [PATCH v3 16/17] Fix schedstat handling

Gregory Haskins
2007-11-17T17:45:25Z

>>> On Sat, Nov 17, 2007 at 1:21 AM, in message
<20071117062405.634159013@goodmis.org>, Steven Rostedt <rostedt@goodmis.org>
wrote:
> Gregory Haskins RT balancing broke sched domains.

Doh! (though you mean s/domains/stats ;)

> This is a fix to allow it to still work.
>
> Signed-off-by: Steven Rostedt <srostedt@redhat.com>
>
> ---
> include/linux/sched.h | 3 ++-
> kernel/sched.c | 17 ++++++++++++++---
> kernel/sched_fair.c | 19 ++++++++++++++-----
> kernel/sched_idletask.c | 3 ++-
> kernel/sched_rt.c | 3 ++-
> 5 files changed, 34 insertions(+), 11 deletions(-)
>
> Index: linux-compile.git/kernel/sched.c
> ===================================================================
> --- linux-compile.git.orig/kernel/sched.c 2007-11-17 00:15:57.000000000 -0500
> +++ linux-compile.git/kernel/sched.c 2007-11-17 00:15:57.000000000 -0500
> @@ -1453,6 +1453,7 @@ static int try_to_wake_up(struct task_st
> unsigned long flags;
> long old_state;
> struct rq *rq;
> + struct sched_domain *this_sd = NULL;
> #ifdef CONFIG_SMP
> int new_cpu;
> #endif
> @@ -1476,10 +1477,20 @@ static int try_to_wake_up(struct task_st
> schedstat_inc(rq, ttwu_count);
> if (cpu == this_cpu)
> schedstat_inc(rq, ttwu_local);
> - else
> - schedstat_inc(rq->sd, ttwu_wake_remote);
> + else {
> +#ifdef CONFIG_SCHEDSTATS
> + struct sched_domain *sd;
> + for_each_domain(this_cpu, sd) {
> + if (cpu_isset(cpu, sd->span)) {
> + schedstat_inc(sd, ttwu_wake_remote);
> + this_sd = sd;
> + break;
> + }
> + }
> +#endif /* CONFIG_SCHEDSTATES */
> + }
>
> - new_cpu = p->sched_class->select_task_rq(p, sync);
> + new_cpu = p->sched_class->select_task_rq(p, this_sd, sync);

I like this optimization, but I am thinking that the location of the stat update is now no longer relevant. It should potentially go *after* the select_task_rq() so that we pick the sched_domain of the actual wake target, not the historical affinity. If that is accurate, I'm sure you can finagle this optimization to work in that scenario too, but it will take a little re-work.

>
> if (new_cpu != cpu) {
> set_task_cpu(p, new_cpu);
> Index: linux-compile.git/include/linux/sched.h
> ===================================================================
> --- linux-compile.git.orig/include/linux/sched.h 2007-11-17 00:15:57.000000000 -0500
> +++ linux-compile.git/include/linux/sched.h 2007-11-17 00:15:57.000000000 -0500
> @@ -823,7 +823,8 @@ struct sched_class {
> void (*enqueue_task) (struct rq *rq, struct task_struct *p, int wakeup);
> void (*dequeue_task) (struct rq *rq, struct task_struct *p, int sleep);
> void (*yield_task) (struct rq *rq);
> - int (*select_task_rq)(struct task_struct *p, int sync);
> + int (*select_task_rq)(struct task_struct *p,
> + struct sched_domain *sd, int sync);
>
> void (*check_preempt_curr) (struct rq *rq, struct task_struct *p);
>
> Index: linux-compile.git/kernel/sched_fair.c
> ===================================================================
> --- linux-compile.git.orig/kernel/sched_fair.c 2007-11-17 00:15:57.000000000 -0500
> +++ linux-compile.git/kernel/sched_fair.c 2007-11-17 00:43:44.000000000 -0500
> @@ -611,11 +611,12 @@ static inline int wake_idle(int cpu, str
> #endif
>
> #ifdef CONFIG_SMP
> -static int select_task_rq_fair(struct task_struct *p, int sync)
> +static int select_task_rq_fair(struct task_struct *p,
> + struct sched_domain *this_sd, int sync)
> {
> int cpu, this_cpu;
> struct rq *rq;
> - struct sched_domain *sd, *this_sd = NULL;
> + struct sched_domain *sd;
> int new_cpu;
>
> cpu = task_cpu(p);
> @@ -623,15 +624,23 @@ static int select_task_rq_fair(struct ta
> this_cpu = smp_processor_id();
> new_cpu = cpu;
>
> + if (cpu == this_cpu || unlikely(!cpu_isset(this_cpu, p->cpus_allowed)))
> + goto out_set_cpu;
> +
> +#ifndef CONFIG_SCHEDSTATS
> + /*
> + * If SCHEDSTATS is configured, then this_sd would
> + * have already been determined.
> + */
> for_each_domain(this_cpu, sd) {
> if (cpu_isset(cpu, sd->span)) {
> this_sd = sd;
> break;
> }
> }
> -
> - if (unlikely(!cpu_isset(this_cpu, p->cpus_allowed)))
> - goto out_set_cpu;
> +#else
> + (void)sd; /* unused */
> +#endif /* CONFIG_SCHEDSTATS */
>
> /*
> * Check for affine wakeup and passive balancing possibilities.
> Index: linux-compile.git/kernel/sched_idletask.c
> ===================================================================
> --- linux-compile.git.orig/kernel/sched_idletask.c 2007-11-17 00:15:57.000000000
> -0500
> +++ linux-compile.git/kernel/sched_idletask.c 2007-11-17 00:15:57.000000000 -0500
> @@ -6,7 +6,8 @@
> */
>
> #ifdef CONFIG_SMP
> -static int select_task_rq_idle(struct task_struct *p, int sync)
> +static int select_task_rq_idle(struct task_struct *p,
> + struct sched_domain *sd, int sync)
> {
> return task_cpu(p); /* IDLE tasks as never migrated */
> }
> Index: linux-compile.git/kernel/sched_rt.c
> ===================================================================
> --- linux-compile.git.orig/kernel/sched_rt.c 2007-11-17 00:15:57.000000000 -0500
> +++ linux-compile.git/kernel/sched_rt.c 2007-11-17 00:44:31.000000000 -0500
> @@ -46,7 +46,8 @@ static void update_rt_migration(struct r
>
> static int find_lowest_rq(struct task_struct *task);
>
> -static int select_task_rq_rt(struct task_struct *p, int sync)
> +static int select_task_rq_rt(struct task_struct *p,
> + struct sched_domain *sd, int sync)
> {
> struct rq *rq = task_rq(p);
>
>
> --