lkml.org 
[lkml]   [2020]   [Jul]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [RFC PATCH 11/16] sched: migration changes for core scheduling(Internet mail)
    From
    Date
    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.
    >>

    \
     
     \ /
      Last update: 2020-07-23 05:37    [W:2.489 / U:0.020 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site