Messages in this thread | | | From | Vincent Guittot <> | Date | Wed, 15 Mar 2023 16:30:36 +0100 | Subject | Re: [PATCH v2] sched/fair: sanitize vruntime of entity being migrated |
| |
On Wed, 15 Mar 2023 at 10:16, Zhang Qiao <zhangqiao22@huawei.com> wrote: > > > > 在 2023/3/14 23:32, Vincent Guittot 写道: > > Le mardi 14 mars 2023 à 14:39:49 (+0100), Vincent Guittot a écrit : > >> On Tue, 14 Mar 2023 at 14:38, Zhang Qiao <zhangqiao22@huawei.com> wrote: > >>> > >>> > >>> > >>> 在 2023/3/14 21:26, Vincent Guittot 写道: > >>>> On Tue, 14 Mar 2023 at 12:03, Zhang Qiao <zhangqiao22@huawei.com> wrote: > >>>>> > >>>>> > >>>>> > >>>>> 在 2023/3/13 22:23, Vincent Guittot 写道: > >>>>>> On Sat, 11 Mar 2023 at 10:57, Zhang Qiao <zhangqiao22@huawei.com> wrote: > >>>>>>> > >>>>>>> > >>>>>>> > >>>>>>> 在 2023/3/10 22:29, Vincent Guittot 写道: > >>>>>>>> Le jeudi 09 mars 2023 à 16:14:38 (+0100), Vincent Guittot a écrit : > >>>>>>>>> On Thu, 9 Mar 2023 at 15:37, Peter Zijlstra <peterz@infradead.org> wrote: > >>>>>>>>>> > >>>>>>>>>> On Thu, Mar 09, 2023 at 03:28:25PM +0100, Peter Zijlstra wrote: > >>>>>>>>>>> On Thu, Mar 09, 2023 at 02:34:05PM +0100, Vincent Guittot wrote: > >>>>>>>>>>> > >>>>>>>>>>>> Then, even if we don't clear exec_start before migrating and keep > >>>>>>>>>>>> current value to be used in place_entity on the new cpu, we can't > >>>>>>>>>>>> compare the rq_clock_task(rq_of(cfs_rq)) of 2 different rqs AFAICT > >>>>>>>>>>> > >>>>>>>>>>> Blergh -- indeed, irq and steal time can skew them between CPUs :/ > >>>>>>>>>>> I suppose we can fudge that... wait_start (which is basically what we're > >>>>>>>>>>> making it do) also does that IIRC. > >>>>>>>>>>> > >>>>>>>>>>> I really dislike having this placement muck spreadout like proposed. > >>>>>>>>>> > >>>>>>>>>> Also, I think we might be over-engineering this, we don't care about > >>>>>>>>>> accuracy at all, all we really care about is 'long-time'. > >>>>>>>>> > >>>>>>>>> you mean taking the patch 1/2 that you mentioned here to add a > >>>>>>>>> migrated field: > >>>>>>>>> https://lore.kernel.org/all/68832dfbb60fda030540b5f4e39c5801942689b1.1648228023.git.tim.c.chen@linux.intel.com/T/#ma5637eb8010f3f4a4abff778af8db705429d003b > >>>>>>>>> > >>>>>>>>> And assume that the divergence between the rq_clock_task() can be ignored ? > >>>>>>>>> > >>>>>>>>> That could probably work but we need to replace the (60LL * > >>>>>>>>> NSEC_PER_SEC) by ((1ULL << 63) / NICE_0_LOAD) because 60sec divergence > >>>>>>>>> would not be unrealistic. > >>>>>>>>> and a comment to explain why it's acceptable > >>>>>>>> > >>>>>>>> Zhang, > >>>>>>>> > >>>>>>>> Could you try the patch below ? > >>>>>>>> This is a rebase/merge/update of: > >>>>>>>> -patch 1/2 above and > >>>>>>>> -https://lore.kernel.org/lkml/20230209193107.1432770-1-rkagan@amazon.de/ > >>>>>>> > >>>>>>> > >>>>>>> I applyed and tested this patch, and it make hackbench slower. > >>>>>>> According to my previous test results. The good result is 82.1(s). > >>>>>>> But the result of this patch is 108.725(s). > >>>>>> > >>>>>> By "the result of this patch is 108.725(s)", you mean the result of > >>>>>> https://lore.kernel.org/lkml/20230209193107.1432770-1-rkagan@amazon.de/ > >>>>>> alone, don't you ? > >>>>> > >>>>> No, with your patch, the test results is 108.725(s), > >>>> > >>>> Ok > >>>> > >>>>> > >>>>> git diff: > >>>>> > >>>>> diff --git a/include/linux/sched.h b/include/linux/sched.h > >>>>> index 63d242164b1a..93a3909ae4c4 100644 > >>>>> --- a/include/linux/sched.h > >>>>> +++ b/include/linux/sched.h > >>>>> @@ -550,6 +550,7 @@ struct sched_entity { > >>>>> struct rb_node run_node; > >>>>> struct list_head group_node; > >>>>> unsigned int on_rq; > >>>>> + unsigned int migrated; > >>>>> > >>>>> u64 exec_start; > >>>>> u64 sum_exec_runtime; > >>>>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > >>>>> index ff4dbbae3b10..e60defc39f6e 100644 > >>>>> --- a/kernel/sched/fair.c > >>>>> +++ b/kernel/sched/fair.c > >>>>> @@ -1057,6 +1057,7 @@ update_stats_curr_start(struct cfs_rq *cfs_rq, struct sched_entity *se) > >>>>> /* > >>>>> * We are starting a new run period: > >>>>> */ > >>>>> + se->migrated = 0; > >>>>> se->exec_start = rq_clock_task(rq_of(cfs_rq)); > >>>>> } > >>>>> > >>>>> @@ -4690,9 +4691,9 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial) > >>>>> * inversed due to s64 overflow. > >>>>> */ > >>>>> sleep_time = rq_clock_task(rq_of(cfs_rq)) - se->exec_start; > >>>>> - if ((s64)sleep_time > 60LL * NSEC_PER_SEC) > >>>>> + if ((s64)sleep_time > (1ULL << 63) / scale_load_down(NICE_0_LOAD) / 2) { > >>>>> se->vruntime = vruntime; > >>>>> - else > >>>>> + } else > >>>>> se->vruntime = max_vruntime(se->vruntime, vruntime); > >>>>> } > >>>>> > >>>>> @@ -7658,8 +7659,7 @@ static void migrate_task_rq_fair(struct task_struct *p, int new_cpu) > >>>>> se->avg.last_update_time = 0; > >>>>> > >>>>> /* We have migrated, no longer consider this task hot */ > >>>>> - se->exec_start = 0; > >>>>> - > >>>>> + se->migrated = 1; > >>>>> update_scan_period(p, new_cpu); > >>>>> } > >>>>> > >>>>> @@ -8343,6 +8343,8 @@ static int task_hot(struct task_struct *p, struct lb_env *env) > >>>>> > >>>>> if (sysctl_sched_migration_cost == 0) > >>>>> return 0; > >>>>> + if (p->se.migrated) > >>>>> + return 0; > >>>>> > >>>>> delta = rq_clock_task(env->src_rq) - p->se.exec_start; > >>>>> > >>>>> > >>>>> > >>>>>> > >>>>>>> > >>>>>>> > >>>>>>>> version1: v6.2 > >>>>>>>> version2: v6.2 + commit 829c1651e9c4 > >>>>>>>> version3: v6.2 + commit 829c1651e9c4 + this patch > >>>>>>>> > >>>>>>>> ------------------------------------------------- > >>>>>>>> version1 version2 version3 > >>>>>>>> test1 81.0 118.1 82.1 > >>>>>>>> test2 82.1 116.9 80.3 > >>>>>>>> test3 83.2 103.9 83.3 > >>>>>>>> avg(s) 82.1 113.0 81.9 > >>>>>> > >>>>>> Ok, it looks like we are back to normal figures > >>>> > >>>> What do those results refer to then ? > >>> > >>> Quote from this email (https://lore.kernel.org/lkml/1cd19d3f-18c4-92f9-257a-378cc18cfbc7@huawei.com/). > >> > >> ok. > >> > >> Then, there is something wrong in my patch. Let me look at it more deeply > > > > Coudl you try the patc below. It fixes the problem on my system > > > > Yes, it fixes the problem. > > ------ > > Performance counter stats for 'hackbench -g 44 -f 20 --process --pipe -l 60000 -s 100' (10 runs): > > 79.53 +- 1.21 seconds time elapsed ( +- 1.52% )
Thanks for testing
> > > > > --- > > kernel/sched/fair.c | 84 +++++++++++++++++++++++++++++++-------------- > > 1 file changed, 59 insertions(+), 25 deletions(-) > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > index 0f499e9a74b5..f8722e47bb0b 100644 > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -4648,23 +4648,36 @@ static void check_spread(struct cfs_rq *cfs_rq, struct sched_entity *se) > > #endif > > } > > > > +static inline bool entity_is_long_sleeper(struct sched_entity *se) > > +{ > > + struct cfs_rq *cfs_rq; > > + u64 sleep_time; > > + > > + if (se->exec_start == 0) > > + return false; > > + > > + cfs_rq = cfs_rq_of(se); > > + > > + sleep_time = rq_clock_task(rq_of(cfs_rq)); > > + > > + /* Happen while migrating because of clock task divergence */ > > + if (sleep_time <= se->exec_start) > > + return false; > > + > > + sleep_time -= se->exec_start; > > + if (sleep_time > ((1ULL << 63) / scale_load_down(NICE_0_LOAD))) > > + return true; > > + > > + return false; > > +} > > + > > static void > > -place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial) > > +place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) > > { > > u64 vruntime = cfs_rq->min_vruntime; > > - u64 sleep_time; > > - > > - /* > > - * The 'current' period is already promised to the current tasks, > > - * however the extra weight of the new task will slow them down a > > - * little, place the new task so that it fits in the slot that > > - * stays open at the end. > > - */ > > - if (initial && sched_feat(START_DEBIT)) > > - vruntime += sched_vslice(cfs_rq, se); > > > > /* sleeps up to a single latency don't count. */ > > - if (!initial) { > > + if (flags & ENQUEUE_WAKEUP) { > > unsigned long thresh; > > > > if (se_is_idle(se)) > > @@ -4680,20 +4693,43 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial) > > thresh >>= 1; > > > > vruntime -= thresh; > > + } else if sched_feat(START_DEBIT) { > > There's a parenthesis missing here.
+1
> > > > + /* > > + * The 'current' period is already promised to the current tasks, > > + * however the extra weight of the new task will slow them down a > > + * little, place the new task so that it fits in the slot that > > + * stays open at the end. > > + */ > > + vruntime += sched_vslice(cfs_rq, se); > > } > > > > /* > > * Pull vruntime of the entity being placed to the base level of > > - * cfs_rq, to prevent boosting it if placed backwards. If the entity > > - * slept for a long time, don't even try to compare its vruntime with > > - * the base as it may be too far off and the comparison may get > > - * inversed due to s64 overflow. > > - */ > > - sleep_time = rq_clock_task(rq_of(cfs_rq)) - se->exec_start; > > - if ((s64)sleep_time > 60LL * NSEC_PER_SEC) > > + * cfs_rq, to prevent boosting it if placed backwards. > > + * However, min_vruntime can advance much faster than real time, with > > + * the exterme being when an entity with the minimal weight always runs > > + * on the cfs_rq. If the new entity slept for long, its vruntime > > + * difference from min_vruntime may overflow s64 and their comparison > > + * may get inversed, so ignore the entity's original vruntime in that > > + * case. > > + * The maximal vruntime speedup is given by the ratio of normal to > > + * minimal weight: scale_load_down(NICE_0_LOAD) / MIN_SHARES. > > + * When placing a migrated waking entity, its exec_start has been set > > + * from a different rq. In order to take into account a possible > > + * divergence between new and prev rq's clocks task because of irq and > > + * stolen time, we take an additional margin. > > + * So, cutting off on the sleep time of > > + * 2^63 / scale_load_down(NICE_0_LOAD) ~ 104 days > > + * should be safe. > > + > > + */ > > + if (entity_is_long_sleeper(se)) > > se->vruntime = vruntime; > > else > > se->vruntime = max_vruntime(se->vruntime, vruntime); > > + > > + if (flags & ENQUEUE_MIGRATED) > > + se->exec_start = 0; > > } > > > > static void check_enqueue_throttle(struct cfs_rq *cfs_rq); > > @@ -4769,7 +4805,7 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) > > account_entity_enqueue(cfs_rq, se); > > > > if (flags & ENQUEUE_WAKEUP) > > - place_entity(cfs_rq, se, 0); > > + place_entity(cfs_rq, se, flags); > > > > check_schedstat_required(); > > update_stats_enqueue_fair(cfs_rq, se, flags); > > @@ -7665,9 +7701,6 @@ static void migrate_task_rq_fair(struct task_struct *p, int new_cpu) > > /* Tell new CPU we are migrated */ > > se->avg.last_update_time = 0; > > > > - /* We have migrated, no longer consider this task hot */ > > - se->exec_start = 0; > > - > > update_scan_period(p, new_cpu); > > } > > > > @@ -11993,7 +12026,7 @@ static void task_fork_fair(struct task_struct *p) > > update_curr(cfs_rq); > > se->vruntime = curr->vruntime; > > } > > - place_entity(cfs_rq, se, 1); > > + place_entity(cfs_rq, se, 0); > > > > if (sysctl_sched_child_runs_first && curr && entity_before(curr, se)) { > > /* > > @@ -12137,8 +12170,9 @@ static void detach_task_cfs_rq(struct task_struct *p) > > /* > > * Fix up our vruntime so that the current sleep doesn't > > * cause 'unlimited' sleep bonus. > > + * This is the same as placing a waking task. > > */ > > - place_entity(cfs_rq, se, 0); > > + place_entity(cfs_rq, se, ENQUEUE_WAKEUP); > > se->vruntime -= cfs_rq->min_vruntime; > > } > > > > -- > > 2.34.1 > > > > > >> > >>> > >>>> > > . > >
| |