Messages in this thread | | | Subject | Re: [RFC PATCH 11/16] sched: migration changes for core scheduling(Internet mail) | From | "Li, Aubrey" <> | Date | Thu, 23 Jul 2020 11:35:56 +0800 |
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On 2020/7/23 10:42, benbjiang(蒋彪) wrote: > Hi, > >> On Jul 23, 2020, at 9:57 AM, Li, Aubrey <aubrey.li@linux.intel.com> wrote: >> >> On 2020/7/22 22:32, benbjiang(蒋彪) wrote: >>> Hi, >>> >>>> On Jul 22, 2020, at 8:13 PM, Li, Aubrey <aubrey.li@linux.intel.com> wrote: >>>> >>>> On 2020/7/22 16:54, benbjiang(蒋彪) wrote: >>>>> Hi, Aubrey, >>>>> >>>>>> On Jul 1, 2020, at 5:32 AM, Vineeth Remanan Pillai <vpillai@digitalocean.com> wrote: >>>>>> >>>>>> From: Aubrey Li <aubrey.li@intel.com> >>>>>> >>>>>> - Don't migrate if there is a cookie mismatch >>>>>> Load balance tries to move task from busiest CPU to the >>>>>> destination CPU. When core scheduling is enabled, if the >>>>>> task's cookie does not match with the destination CPU's >>>>>> core cookie, this task will be skipped by this CPU. This >>>>>> mitigates the forced idle time on the destination CPU. >>>>>> >>>>>> - Select cookie matched idle CPU >>>>>> In the fast path of task wakeup, select the first cookie matched >>>>>> idle CPU instead of the first idle CPU. >>>>>> >>>>>> - Find cookie matched idlest CPU >>>>>> In the slow path of task wakeup, find the idlest CPU whose core >>>>>> cookie matches with task's cookie >>>>>> >>>>>> - Don't migrate task if cookie not match >>>>>> For the NUMA load balance, don't migrate task to the CPU whose >>>>>> core cookie does not match with task's cookie >>>>>> >>>>>> Signed-off-by: Aubrey Li <aubrey.li@linux.intel.com> >>>>>> Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com> >>>>>> Signed-off-by: Vineeth Remanan Pillai <vpillai@digitalocean.com> >>>>>> --- >>>>>> kernel/sched/fair.c | 64 ++++++++++++++++++++++++++++++++++++++++---- >>>>>> kernel/sched/sched.h | 29 ++++++++++++++++++++ >>>>>> 2 files changed, 88 insertions(+), 5 deletions(-) >>>>>> >>>>>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >>>>>> index d16939766361..33dc4bf01817 100644 >>>>>> --- a/kernel/sched/fair.c >>>>>> +++ b/kernel/sched/fair.c >>>>>> @@ -2051,6 +2051,15 @@ static void task_numa_find_cpu(struct task_numa_env *env, >>>>>> if (!cpumask_test_cpu(cpu, env->p->cpus_ptr)) >>>>>> continue; >>>>>> >>>>>> +#ifdef CONFIG_SCHED_CORE >>>>>> + /* >>>>>> + * Skip this cpu if source task's cookie does not match >>>>>> + * with CPU's core cookie. >>>>>> + */ >>>>>> + if (!sched_core_cookie_match(cpu_rq(cpu), env->p)) >>>>>> + continue; >>>>>> +#endif >>>>>> + >>>>>> env->dst_cpu = cpu; >>>>>> if (task_numa_compare(env, taskimp, groupimp, maymove)) >>>>>> break; >>>>>> @@ -5963,11 +5972,17 @@ find_idlest_group_cpu(struct sched_group *group, struct task_struct *p, int this >>>>>> >>>>>> /* Traverse only the allowed CPUs */ >>>>>> for_each_cpu_and(i, sched_group_span(group), p->cpus_ptr) { >>>>>> + struct rq *rq = cpu_rq(i); >>>>>> + >>>>>> +#ifdef CONFIG_SCHED_CORE >>>>>> + if (!sched_core_cookie_match(rq, p)) >>>>>> + continue; >>>>>> +#endif >>>>>> + >>>>>> if (sched_idle_cpu(i)) >>>>>> return i; >>>>>> >>>>>> if (available_idle_cpu(i)) { >>>>>> - struct rq *rq = cpu_rq(i); >>>>>> struct cpuidle_state *idle = idle_get_state(rq); >>>>>> if (idle && idle->exit_latency < min_exit_latency) { >>>>>> /* >>>>>> @@ -6224,8 +6239,18 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t >>>>>> for_each_cpu_wrap(cpu, cpus, target) { >>>>>> if (!--nr) >>>>>> return -1; >>>>>> - if (available_idle_cpu(cpu) || sched_idle_cpu(cpu)) >>>>>> - break; >>>>>> + >>>>>> + if (available_idle_cpu(cpu) || sched_idle_cpu(cpu)) { >>>>>> +#ifdef CONFIG_SCHED_CORE >>>>>> + /* >>>>>> + * If Core Scheduling is enabled, select this cpu >>>>>> + * only if the process cookie matches core cookie. >>>>>> + */ >>>>>> + if (sched_core_enabled(cpu_rq(cpu)) && >>>>>> + p->core_cookie == cpu_rq(cpu)->core->core_cookie) >>>>> Why not also add similar logic in select_idle_smt to reduce forced-idle? :) >>>> We hit select_idle_smt after we scaned the entire LLC domain for idle cores >>>> and idle cpus and failed,so IMHO, an idle smt is probably a good choice under >>>> this scenario. >>> >>> AFAIC, selecting idle sibling with unmatched cookie will cause unnecessary fored-idle, unfairness and latency, compared to choosing *target* cpu. >> Choosing target cpu could increase the runnable task number on the target runqueue, this >> could trigger busiest->nr_running > 1 logic and makes the idle sibling trying to pull but >> not success(due to cookie not match). Putting task to the idle sibling is relatively stable IMHO. > > I’m afraid that *unsuccessful* pullings between smts would not result in unstableness, because > the load-balance always do periodicly , and unsuccess means nothing happen. unsuccess pulling means more unnecessary overhead in load balance.
> On the contrary, unmatched sibling tasks running concurrently could bring forced-idle to each other repeatedly, > Which is more unstable, and more costly when pick_next_task for all siblings. Not worse than two tasks ping-pong on the same target run queue I guess, and better if - task1(cookie A) is running on the target, and task2(cookie B) in the runqueue, - task3(cookie B) coming
If task3 chooses target's sibling, it could have a chance to run concurrently with task2. But if task3 chooses target, it will wait for next pulling luck of load balancer
Thanks, -Aubrey
> In consideration of currently load-balance being not fully aware of core-scheduling, and can not improve > the *unmatched sibling* case, the *find_idlest_** entry should try its best to avoid the case, IMHO.
> Also, just an advice and an option. :) > > Thx. > Regards, > Jiang > >> >>> Besides, choosing *target* cpu may be more cache friendly. So IMHO, *target* cpu may be a better choice if cookie not match, instead of idle sibling. >> I'm not sure if it's more cache friendly as the target is busy, and the coming task >> is a cookie unmatched task. >>
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