-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 07/28/2014 04:23 AM, Vincent Guittot wrote: > On 25 July 2014 21:32, Rik van Riel <[email protected]> wrote: >> Subject: sched: make update_sd_pick_busiest return true on a >> busier sd >> >> Currently update_sd_pick_busiest only identifies the busiest sd >> that is either overloaded, or has a group imbalance. When no sd >> is imbalanced or overloaded, the load balancer fails to find the >> busiest domain. >> >> This breaks load balancing between domains that are not >> overloaded, in the !SD_ASYM_PACKING case. This patch makes >> update_sd_pick_busiest return true when the busiest sd yet is >> encountered. >> >> Behaviour for SD_ASYM_PACKING does not seem to match the >> comment, but I have no hardware to test that so I have left the >> behaviour of that code unchanged. >> >> It is unclear what to do with the group_imb condition. Should >> group_imb override a busier load? If so, should we fix > > IMHO, group_imb should have a lower priority compared to > overloaded group because it generates active migration whereas the > use of overloaded group could solve the imbalance with normal > migration Then, AFAICT, we already have a special way to compute > imbalance when group_imb is set > >> calculate_imbalance to return a sensible number when the >> "busiest" node found has a below average load? We probably need >> to fix calculate_imbalance anyway, to deal with an overloaded >> group that happens to have a below average load... >> >> Cc: [email protected] Cc: [email protected] Signed-off-by: Rik >> van Riel <[email protected]> --- kernel/sched/fair.c | 18 >> +++++++++++++----- 1 file changed, 13 insertions(+), 5 >> deletions(-) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index >> 45943b2..c96044f 100644 --- a/kernel/sched/fair.c +++ >> b/kernel/sched/fair.c @@ -5949,6 +5949,11 @@ static inline void >> update_sg_lb_stats(struct lb_env *env, >> sgs->group_has_free_capacity = 1; } >> >> +static bool group_overloaded(struct sg_lb_stats *sgs) +{ + >> return sgs->sum_nr_running > sgs->group_capacity_factor; +} + >> /** * update_sd_pick_busiest - return 1 on busiest group * @env: >> The load balancing environment. @@ -5957,7 +5962,7 @@ static >> inline void update_sg_lb_stats(struct lb_env *env, * @sgs: >> sched_group statistics * * Determine if @sg is a busier group >> than the previously selected - * busiest group. + * busiest >> group. * * Return: %true if @sg is a busier group than the >> previously selected * busiest group. %false otherwise. @@ >> -5967,13 +5972,17 @@ static bool update_sd_pick_busiest(struct >> lb_env *env, struct sched_group *sg, struct sg_lb_stats *sgs) { + >> if (group_overloaded(sgs) && >> !group_overloaded(&sds->busiest_stat)) > > The 1st time you run update_sd_pick_busiest, group_capacity_factor > and sum_nr_running of sds->busiest_stat are uninitialized.
Good point, init_sd_lb_stats only zeroes out a few fields. I will fix this in the next version. >> + return true; + > > IIUC your new test sequence, you haven't solved the following use > case: Fixed in the next version, with Peter's idea. - -- All rights reversed -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQEcBAEBAgAGBQJT1mZ8AAoJEM553pKExN6DpPAH/A+a9Lbz/pV8uFGG3RRrs2gI l8rhgtVLEM0uiDTDavB/D1GBnWcxfNbg6o/yF7dTXDA+sWltztZISi6dZ9JpEhww 0wK3rOD6t+VYpu6OaA2rIp2p2o12ou2d8ipjimjGf9gGD8i6vZiGOfTytsSateZH X9pSQ5Tv63ES8m3DeLcXEy+YQVunyLD83aTwSpziBFKUGguttTvvqEx5MutxVQyA Wx7hqX4VTR2oC3mS6djzK/hp0OmpZL4WKmnqUgjm11k0+UvBc1MnYE937CHixOdQ GjfIgk+G8EGVucbKFfhgwrNFfemL4MXxSVxMMor1lMFt9yFKcwoSMRS40mcH+Rw= =qENP -----END PGP SIGNATURE----- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
