On 2020/11/30 17:33, Balbir Singh wrote:
> On Thu, Nov 26, 2020 at 05:26:31PM +0800, Li, Aubrey wrote:
>> On 2020/11/26 16:32, Balbir Singh wrote:
>>> On Thu, Nov 26, 2020 at 11:20:41AM +0800, Li, Aubrey wrote:
>>>> On 2020/11/26 6:57, Balbir Singh wrote:
>>>>> On Wed, Nov 25, 2020 at 11:12:53AM +0800, Li, Aubrey wrote:
>>>>>> On 2020/11/24 23:42, Peter Zijlstra wrote:
>>>>>>> On Mon, Nov 23, 2020 at 12:36:10PM +0800, Li, Aubrey wrote:
>>>>>>>>>> +#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
>>>>>>>>>> +
>>>>>>>>>
>>>>>>>>> Any reason this is under an #ifdef? In sched_core_cookie_match() won't
>>>>>>>>> the check for sched_core_enabled() do the right thing even when
>>>>>>>>> CONFIG_SCHED_CORE is not enabed?>
>>>>>>>> Yes, sched_core_enabled works properly when CONFIG_SCHED_CORE is not
>>>>>>>> enabled. But when CONFIG_SCHED_CORE is not enabled, it does not make
>>>>>>>> sense to leave a core scheduler specific function here even at compile
>>>>>>>> time. Also, for the cases in hot path, this saves CPU cycles to avoid
>>>>>>>> a judgment.
>>>>>>>
>>>>>>> No, that's nonsense. If it works, remove the #ifdef. Less (#ifdef) is
>>>>>>> more.
>>>>>>>
>>>>>>
>>>>>> Okay, I pasted the refined patch here.
>>>>>> @Joel, please let me know if you want me to send it in a separated
>>>>>> thread.
>>>>>>
>>>>>
>>>>> You still have a bunch of #ifdefs, can't we just do
>>>>>
>>>>> #ifndef CONFIG_SCHED_CORE
>>>>> static inline bool sched_core_enabled(struct rq *rq)
>>>>> {
>>>>> return false;
>>>>> }
>>>>> #endif
>>>>>
>>>>> and frankly I think even that is not needed because there is a jump
>>>>> label __sched_core_enabled that tells us if sched_core is enabled or
>>>>> not.
>>>>
>>>> Hmm..., I need another wrapper for CONFIG_SCHED_CORE specific variables.
>>>> How about this one?
>>>>
>>>
>>> Much better :)
>>>
>>>> Thanks,
>>>> -Aubrey
>>>>
>>>> From 61dac9067e66b5b9ea26c684c8c8235714bab38a Mon Sep 17 00:00:00 2001
>>>> From: Aubrey Li <aubrey...@linux.intel.com>
>>>> Date: Thu, 26 Nov 2020 03:08:04 +0000
>>>> Subject: [PATCH] sched: migration changes for core scheduling
>>>>
>>>> - 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
>>>>
>>>> Tested-by: Julien Desfossez <jdesfos...@digitalocean.com>
>>>> Signed-off-by: Aubrey Li <aubrey...@linux.intel.com>
>>>> Signed-off-by: Tim Chen <tim.c.c...@linux.intel.com>
>>>> Signed-off-by: Vineeth Remanan Pillai <virem...@linux.microsoft.com>
>>>> Signed-off-by: Joel Fernandes (Google) <j...@joelfernandes.org>
>>>> ---
>>>> kernel/sched/fair.c | 57 ++++++++++++++++++++++++++++++++++++++++----
>>>> kernel/sched/sched.h | 43 +++++++++++++++++++++++++++++++++
>>>> 2 files changed, 95 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>>>> index de82f88ba98c..70dd013dff1d 100644
>>>> --- a/kernel/sched/fair.c
>>>> +++ b/kernel/sched/fair.c
>>>> @@ -1921,6 +1921,13 @@ static void task_numa_find_cpu(struct task_numa_env
>>>> *env,
>>>> if (!cpumask_test_cpu(cpu, env->p->cpus_ptr))
>>>> continue;
>>>>
>>>> + /*
>>>> + * 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;
>>>> +
>>>> env->dst_cpu = cpu;
>>>> if (task_numa_compare(env, taskimp, groupimp, maymove))
>>>> break;
>>>> @@ -5867,11 +5874,15 @@ 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);
>>>> +
>>>> + if (!sched_core_cookie_match(rq, p))
>>>> + continue;
>>>> +
>>>> 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) {
>>>> /*
>>>> @@ -6129,8 +6140,19 @@ 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)) {
>>>> + /*
>>>> + * If Core Scheduling is enabled, select this cpu
>>>> + * only if the process cookie matches core cookie.
>>>> + */
>>>> + if (sched_core_enabled(cpu_rq(cpu))) {
>>>> + if (__cookie_match(cpu_rq(cpu), p))
>>>> + break;
>>>> + } else {
>>>> + break;
>>>> + }
>>>> + }
>>>
>>> Isn't this better and equivalent?
>>>
>>> if ((available_idle_cpu(cpu) || sched_idle_cpu(cpu)) &&
>>> sched_core_cookie_match(cpu_rq(cpu), p))
>>> break;
>>>
>>
>>
>> That's my previous implementation in the earlier version.
>> But since here is the hot code path, we want to remove the idle
>> core check in sched_core_cookie_match.
>
> I see, so we basically need a jump label, if sched_core_cookie_match
> can be inlined with a check for sched_core_enabled() upfront, it might
> solve a lot of the concern, readability of this section of code is not
> the best.
>
>>
>>>> }
>>>>
>>>> time = cpu_clock(this) - time;
>>>> @@ -7530,8 +7552,9 @@ int can_migrate_task(struct task_struct *p, struct
>>>> lb_env *env)
>>>> * We do not migrate tasks that are:
>>>> * 1) throttled_lb_pair, or
>>>> * 2) cannot be migrated to this CPU due to cpus_ptr, or
>>>> - * 3) running (obviously), or
>>>> - * 4) are cache-hot on their current CPU.
>>>> + * 3) task's cookie does not match with this CPU's core cookie
>>>> + * 4) running (obviously), or
>>>> + * 5) are cache-hot on their current CPU.
>>>> */
>>>> if (throttled_lb_pair(task_group(p), env->src_cpu, env->dst_cpu))
>>>> return 0;
>>>> @@ -7566,6 +7589,13 @@ int can_migrate_task(struct task_struct *p, struct
>>>> lb_env *env)
>>>> return 0;
>>>> }
>>>>
>>>> + /*
>>>> + * Don't migrate task if the task's cookie does not match
>>>> + * with the destination CPU's core cookie.
>>>> + */
>>>> + if (!sched_core_cookie_match(cpu_rq(env->dst_cpu), p))
>>>> + return 0;
>>>> +
>>>> /* Record that we found atleast one task that could run on dst_cpu */
>>>> env->flags &= ~LBF_ALL_PINNED;
>>>>
>>>> @@ -8792,6 +8822,23 @@ find_idlest_group(struct sched_domain *sd, struct
>>>> task_struct *p, int this_cpu)
>>>> p->cpus_ptr))
>>>> continue;
>>>>
>>>> + if (sched_core_enabled(cpu_rq(this_cpu))) {
>>>> + int i = 0;
>>>> + bool cookie_match = false;
>>>> +
>>>> + for_each_cpu(i, sched_group_span(group)) {
>>>> + struct rq *rq = cpu_rq(i);
>>>> +
>>>> + if (sched_core_cookie_match(rq, p)) {
>>>> + cookie_match = true;
>>>> + break;
>>>> + }
>>>> + }
>>>> + /* Skip over this group if no cookie matched */
>>>> + if (!cookie_match)
>>>> + continue;
>>>> + }
>>>> +
>>>
>>> Again, I think this can be refactored because sched_core_cookie_match checks
>>> for sched_core_enabled()
>>>
>>> int i = 0;
>>> bool cookie_match = false;
>>> for_each_cpu(i, sched_group_span(group)) {
>>> if (sched_core_cookie_match(cpu_rq(i), p))
>>> break;
>>> }
>>> if (i >= nr_cpu_ids)
>>> continue;
>>
>> There is a loop here when CONFIG_SCHED_CORE=n, which is unwanted I guess.
>>
>
> Yes, potentially, may be abstract the for_each_cpu into a function and then
> optimize out the case for SCHED_CORE=n, I feel all the extra checks in the
> various places make the code hard to read.
Okay, I see your point, let me try if I can make it better.
Thanks,
-Aubrey
