On Wed, Mar 18, 2015 at 02:31:02PM +0800, Xunlei Pang wrote:
> From: Xunlei Pang <pang.xun...@linaro.org>
>
> In load_balance(), some members of lb_env will be assigned with
> new values in LBF_DST_PINNED case. But lb_env::flags may still
> retain LBF_ALL_PINNED if no proper tasks were found afterwards
> due to another balance, task affinity changing, etc, which can
> really happen because busiest rq lock has already been released.
Sure..
> This is wrong, for example with env.dst_cpu assigned new_dst_cpu
> when going back to "redo" label, it may cause should_we_balance()
> to return false which is unreasonable.
Why? You've got a very unlikely, very hard case, its unlikely that
anything we do will substantially improve the situation, but you make
the code uglier for it.
> This patch restores proper status of env before "goto redo", and
> improves "out_all_pinned" and "out_one_pinned" labels.
That doesn't even begin to explain half of what the patch does.
> @@ -6977,12 +6978,19 @@ more_balance:
> /* All tasks on this runqueue were pinned by CPU affinity */
> if (unlikely(env.flags & LBF_ALL_PINNED)) {
> cpumask_clear_cpu(cpu_of(busiest), cpus);
> - if (!cpumask_empty(cpus)) {
> - env.loop = 0;
> - env.loop_break = sched_nr_migrate_break;
> - goto redo;
> + if (env.new_dst_cpu != -1) {
I really don't get this, how can this not be?
> + env.new_dst_cpu = -1;
> + cpumask_or(cpus, cpus,
> + sched_group_cpus(sd->groups));
> + cpumask_and(cpus, cpus, cpu_active_mask);
More unexplained magic, why is this right?
The rest of the patch isn't much better.
--
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/
