| Message ID | 1404144343-18720-3-git-send-email-vincent.guittot@linaro.org |
|---|---|
| State | Superseded |
| Headers | show |
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 06/30/2014 12:05 PM, Vincent Guittot wrote: > I have tried to understand the meaning of the condition : > (this_load <= load && this_load + target_load(prev_cpu, idx) <= > tl_per_task) but i failed to find a use case that can take > advantage of it and i haven't found clear description in the > previous commits' log. Futhermore, the comment of the condition > refers to the task_hot function that was used before being replaced > by the current condition: /* * This domain has SD_WAKE_AFFINE and * > p is cache cold in this domain, and * there is no bad imbalance. > */ > > If we look more deeply the below condition this_load + > target_load(prev_cpu, idx) <= tl_per_task > > When sync is clear, we have : tl_per_task = runnable_load_avg / > nr_running this_load = max(runnable_load_avg, cpuload[idx]) > target_load = max(runnable_load_avg', cpuload'[idx]) > > It implies that runnable_load_avg' == 0 and nr_running <= 1 in > order to match the condition. This implies that runnable_load_avg > == 0 too because of the condition: this_load <= load but if this > _load is null, balanced is already set and the test is redundant. > > If sync is set, it's not as straight forward as above (especially > if cgroup are involved) but the policy should be similar as we have > removed a task that's going to sleep in order to get a more > accurate load and this_load values. > > The current conclusion is that these additional condition don't > give any benefit so we can remove them. > > Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> Acked-by: Rik van Riel <riel@redhat.com> - -- All rights reversed -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQEcBAEBAgAGBQJTvLG+AAoJEM553pKExN6DfhMH/iYJAS/nCq1teCNm39zZg1bF MIp2iWwnB5VTQvwVLQ3FaGU80oWScUez8zjn26LjPp5SnxyDEwG0YVM3/57EyJme PgffmP8xsVJwRkKnO4VRR0Go2EMXl9cdf9exe6lFjRyv4/Z15o9NZsDmX8JcLmG+ JPKq4DnMpJ3LiMiVuwwYtYSLk/tCHCPLnie4Z/WznlHk220WciVXFZG7AQI2AHXj pMkZ5TWQODW7PEec+8dGzDnFcdXPftRYWCKLXG+9NM92YQpIsK8nZdC8rJeXhjBC 9VNb8QNZ6yVd0lvOSxy0drOV9BFXUImF6lsLxA12oHE6TLm6FeiHTG9X4xGOhN0= =XlY9 -----END PGP SIGNATURE----- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 0c48dff..c6dba48 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4241,7 +4241,6 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync) { s64 this_load, load; int idx, this_cpu, prev_cpu; - unsigned long tl_per_task; struct task_group *tg; unsigned long weight; int balanced; @@ -4299,32 +4298,15 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync) balanced = this_eff_load <= prev_eff_load; } else balanced = true; - - /* - * If the currently running task will sleep within - * a reasonable amount of time then attract this newly - * woken task: - */ - if (sync && balanced) - return 1; - schedstat_inc(p, se.statistics.nr_wakeups_affine_attempts); - tl_per_task = cpu_avg_load_per_task(this_cpu); - if (balanced || - (this_load <= load && - this_load + target_load(prev_cpu, idx) <= tl_per_task)) { - /* - * This domain has SD_WAKE_AFFINE and - * p is cache cold in this domain, and - * there is no bad imbalance. - */ - schedstat_inc(sd, ttwu_move_affine); - schedstat_inc(p, se.statistics.nr_wakeups_affine); + if (!balanced) + return 0; - return 1; - } - return 0; + schedstat_inc(sd, ttwu_move_affine); + schedstat_inc(p, se.statistics.nr_wakeups_affine); + + return 1; } /*
I have tried to understand the meaning of the condition : (this_load <= load && this_load + target_load(prev_cpu, idx) <= tl_per_task) but i failed to find a use case that can take advantage of it and i haven't found clear description in the previous commits' log. Futhermore, the comment of the condition refers to the task_hot function that was used before being replaced by the current condition: /* * This domain has SD_WAKE_AFFINE and * p is cache cold in this domain, and * there is no bad imbalance. */ If we look more deeply the below condition this_load + target_load(prev_cpu, idx) <= tl_per_task When sync is clear, we have : tl_per_task = runnable_load_avg / nr_running this_load = max(runnable_load_avg, cpuload[idx]) target_load = max(runnable_load_avg', cpuload'[idx]) It implies that runnable_load_avg' == 0 and nr_running <= 1 in order to match the condition. This implies that runnable_load_avg == 0 too because of the condition: this_load <= load but if this _load is null, balanced is already set and the test is redundant. If sync is set, it's not as straight forward as above (especially if cgroup are involved) but the policy should be similar as we have removed a task that's going to sleep in order to get a more accurate load and this_load values. The current conclusion is that these additional condition don't give any benefit so we can remove them. Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> --- kernel/sched/fair.c | 30 ++++++------------------------ 1 file changed, 6 insertions(+), 24 deletions(-)