On Tue, 16 Dec 2008, Mike Galbraith wrote: > On Tue, 2008-12-16 at 01:49 +0100, Miklos Szeredi wrote: > > On Sat, 13 Dec 2008, Rafael J. Wysocki wrote: > > > Bug-Entry : http://bugzilla.kernel.org/show_bug.cgi?id=12208 > > > Subject : uml is very slow on 2.6.28 host > > > Submitter : Miklos Szeredi <miklos@xxxxxxxxxx> > > > Date : 2008-12-12 9:35 (2 days old) > > > References : http://marc.info/?l=linux-kernel&m=122907463518593&w=4 > > > > I did a bisection, and this is the commit which is responsible: > > > > commit 464b75273f64be7c81fee975bd6ca9593df3427b > > Author: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> > > Date: Fri Oct 24 11:06:15 2008 +0200 > > > > sched: re-instate vruntime based wakeup preemption > > > > The advantage is that vruntime based wakeup preemption has a better > > conceptual model. Here wakeup_gran = 0 means: preempt when 'fair'. > > Therefore wakeup_gran is the granularity of unfairness we allow in order > > to make progress. > > > > Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> > > Acked-by: Mike Galbraith <efault@xxxxxx> > > Signed-off-by: Ingo Molnar <mingo@xxxxxxx> > > If that commit is responsible, then it should also be very slow in pre > 28 kernels, where the same exists. Everything prior to 2.6.28 was fine in this respect, so there must be some subtle difference. > Hm, there's another possibility. > Can you try echo NO_LAST_BUDDY > /sys/kernel/debug/sched_features? It didn't help, unfortunately. Applying this patch on top of latest git (which essentially reverts the above commit) fixes the slowness. Thanks, Miklos --- kernel/sched_fair.c | 98 +++------------------------------------------------- 1 file changed, 6 insertions(+), 92 deletions(-) Index: linux.git/kernel/sched_fair.c =================================================================== --- linux.git.orig/kernel/sched_fair.c 2008-12-16 01:34:26.000000000 +0100 +++ linux.git/kernel/sched_fair.c 2008-12-16 01:34:54.000000000 +0100 @@ -143,49 +143,6 @@ static inline struct sched_entity *paren return se->parent; } -/* return depth at which a sched entity is present in the hierarchy */ -static inline int depth_se(struct sched_entity *se) -{ - int depth = 0; - - for_each_sched_entity(se) - depth++; - - return depth; -} - -static void -find_matching_se(struct sched_entity **se, struct sched_entity **pse) -{ - int se_depth, pse_depth; - - /* - * preemption test can be made between sibling entities who are in the - * same cfs_rq i.e who have a common parent. Walk up the hierarchy of - * both tasks until we find their ancestors who are siblings of common - * parent. - */ - - /* First walk up until both entities are at same depth */ - se_depth = depth_se(*se); - pse_depth = depth_se(*pse); - - while (se_depth > pse_depth) { - se_depth--; - *se = parent_entity(*se); - } - - while (pse_depth > se_depth) { - pse_depth--; - *pse = parent_entity(*pse); - } - - while (!is_same_group(*se, *pse)) { - *se = parent_entity(*se); - *pse = parent_entity(*pse); - } -} - #else /* CONFIG_FAIR_GROUP_SCHED */ static inline struct rq *rq_of(struct cfs_rq *cfs_rq) @@ -236,11 +193,6 @@ static inline struct sched_entity *paren return NULL; } -static inline void -find_matching_se(struct sched_entity **se, struct sched_entity **pse) -{ -} - #endif /* CONFIG_FAIR_GROUP_SCHED */ @@ -1291,8 +1243,8 @@ static unsigned long wakeup_gran(struct * More easily preempt - nice tasks, while not making it harder for * + nice tasks. */ - if (!sched_feat(ASYM_GRAN) || se->load.weight > NICE_0_LOAD) - gran = calc_delta_fair(sysctl_sched_wakeup_granularity, se); + if (sched_feat(ASYM_GRAN)) + gran = calc_delta_mine(gran, NICE_0_LOAD, &se->load); return gran; } @@ -1345,6 +1268,7 @@ static void check_preempt_wakeup(struct { struct task_struct *curr = rq->curr; struct sched_entity *se = &curr->se, *pse = &p->se; + s64 delta_exec; if (unlikely(rt_prio(p->prio))) { struct cfs_rq *cfs_rq = task_cfs_rq(curr); @@ -1398,19 +1322,9 @@ static void check_preempt_wakeup(struct return; } - find_matching_se(&se, &pse); - - while (se) { - BUG_ON(!pse); - - if (wakeup_preempt_entity(se, pse) == 1) { - resched_task(curr); - break; - } - - se = parent_entity(se); - pse = parent_entity(pse); - } + delta_exec = se->sum_exec_runtime - se->prev_sum_exec_runtime; + if (delta_exec > wakeup_gran(pse)) + resched_task(curr); } static struct task_struct *pick_next_task_fair(struct rq *rq) -- To unsubscribe from this list: send the line "unsubscribe kernel-testers" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
