lkml.org 
[lkml]   [2017]   [Dec]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC PATCH] sched: Improve scalability of select_idle_sibling using SMT balance
On Fri, Dec 08, 2017 at 12:07:54PM -0800, subhra mazumdar wrote:
> +static inline void
> +sd_context_switch(struct sched_domain *sd, struct rq *rq, int util)
> +{
> + struct sched_group *sg_cpu;
> +
> + /* atomically add/subtract the util */
> + sg_cpu = sd->sg_cpu;
> + if (util > 0)
> + atomic_inc(
> + (atomic_t *)(&(sg_cpu->utilization)));
> + else
> + atomic_dec(
> + (atomic_t *)(&(sg_cpu->utilization)));

Whahah, lol, no!

> +}
> +
> /*
> * context_switch - switch to the new MM and the new thread's register state.
> */
> @@ -2751,6 +2766,51 @@ context_switch(struct rq *rq, struct task_struct *prev,
> struct task_struct *next, struct rq_flags *rf)
> {
> struct mm_struct *mm, *oldmm;
> + int this_cpu = rq->cpu;
> + struct sched_domain *sd;
> + unsigned int cond;
> +
> + cond = ((prev != rq->idle) << 1) | (next != rq->idle);
> + sd = rcu_dereference(per_cpu(sd_llc, this_cpu));

That one is RCU, not RCU-sched protected..

> + /*
> + * From sd_llc downward update the SMT utilization.
> + * Skip the lowest level 0.
> + */
> + for_each_lower_domain(sd) {
> + if (sd->level == 0)
> + break;
> + if (rq->initial_util == UTIL_UNINITIALIZED) {
> + switch (cond) {
> + case PREV_IDLE_NEXT_NIDLE:
> + case PREV_NIDLE_NEXT_NIDLE:
> + sd_context_switch(sd, rq, SMT_THREAD_UTIL);
> + break;
> + case PREV_NIDLE_NEXT_IDLE:
> + case PREV_IDLE_NEXT_IDLE:
> + break;
> + }
> + } else {
> + switch (cond) {
> + case PREV_IDLE_NEXT_NIDLE:
> + sd_context_switch(sd, rq, SMT_THREAD_UTIL);
> + break;
> + case PREV_NIDLE_NEXT_IDLE:
> + sd_context_switch(sd, rq, -SMT_THREAD_UTIL);
> + break;
> + case PREV_IDLE_NEXT_IDLE:
> + case PREV_NIDLE_NEXT_NIDLE:
> + break;
> + }
> + }
> + }
> +
> + if (sd) {
> + if (next == rq->idle)
> + rq->initial_util = UTIL_IDLE;
> + else
> + rq->initial_util = UTIL_BUSY;
> + }

WTH do you even think this is reasonable?

> prepare_task_switch(rq, prev, next);
>

And I still have no idea what the patch does, but I can't be bothered to
reverse engineer it just now.

\
 
 \ /
  Last update: 2017-12-19 20:46    [W:0.109 / U:0.132 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site