On Wed, Jul 08, 2015 at 08:13:46AM +0200, Mike Galbraith wrote:
>
> +/*
> + * Detect 1:N waker/wakee relationship via a switching-frequency heuristic.
> + * A waker of many should wake a different task than the one last awakened
> + * at a frequency roughly N times higher than one of its wakees. In order
> + * to determine whether we should let the load spread vs consolodating to
> + * shared cache, we look for a minimum 'flip' frequency of llc_size in one
> + * partner, and a factor of lls_size higher frequency in the other. With
> + * both conditions met, we can be relatively sure that we are seeing a 1:N
> + * relationship, and that load size exceeds socket size.
> + */
> static int wake_wide(struct task_struct *p)
> {
> + unsigned int waker_flips = current->wakee_flips;
> + unsigned int wakee_flips = p->wakee_flips;
> int factor = this_cpu_read(sd_llc_size);
>
> + if (waker_flips < wakee_flips)
> + swap(waker_flips, wakee_flips);
This makes the wakee/waker names useless, the end result is more like
wakee_flips := client_flips, waker_flips := server_flips.
> + if (wakee_flips < factor || waker_flips < wakee_flips * factor)
> + return 0;
I don't get the first condition... why would the client ever flip? It
only talks to that one server.
> + return 1;
> }
> @@ -5021,14 +5015,17 @@ select_task_rq_fair(struct task_struct *
> {
> struct sched_domain *tmp, *affine_sd = NULL, *sd = NULL;
> int cpu = smp_processor_id();
> + int new_cpu = prev_cpu;
> int want_affine = 0;
> int sync = wake_flags & WF_SYNC;
>
> rcu_read_lock();
> + if (sd_flag & SD_BALANCE_WAKE) {
> + want_affine = !wake_wide(p) && cpumask_test_cpu(cpu,
> tsk_cpus_allowed(p));
> + if (!want_affine)
> + goto select_idle;
> + }
So this preserves/makes worse the bug Morten spotted, even without
want_affine we should still attempt SD_BALANCE_WAKE if set.
> +
> for_each_domain(cpu, tmp) {
> if (!(tmp->flags & SD_LOAD_BALANCE))
> continue;
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
