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Message-ID: <e885eebe-686c-70f7-95b9-17a065fb2764@linux.intel.com>
Date: Thu, 26 Nov 2020 17:26:31 +0800
From: "Li, Aubrey" <aubrey.li@...ux.intel.com>
To: Balbir Singh <bsingharora@...il.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
"Joel Fernandes (Google)" <joel@...lfernandes.org>,
Nishanth Aravamudan <naravamudan@...italocean.com>,
Julien Desfossez <jdesfossez@...italocean.com>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Vineeth Pillai <viremana@...ux.microsoft.com>,
Aaron Lu <aaron.lwe@...il.com>,
Aubrey Li <aubrey.intel@...il.com>, tglx@...utronix.de,
linux-kernel@...r.kernel.org, mingo@...nel.org,
torvalds@...ux-foundation.org, fweisbec@...il.com,
keescook@...omium.org, kerrnel@...gle.com,
Phil Auld <pauld@...hat.com>,
Valentin Schneider <valentin.schneider@....com>,
Mel Gorman <mgorman@...hsingularity.net>,
Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
Paolo Bonzini <pbonzini@...hat.com>, vineeth@...byteword.org,
Chen Yu <yu.c.chen@...el.com>,
Christian Brauner <christian.brauner@...ntu.com>,
Agata Gruza <agata.gruza@...el.com>,
Antonio Gomez Iglesias <antonio.gomez.iglesias@...el.com>,
graf@...zon.com, konrad.wilk@...cle.com, dfaggioli@...e.com,
pjt@...gle.com, rostedt@...dmis.org, derkling@...gle.com,
benbjiang@...cent.com,
Alexandre Chartre <alexandre.chartre@...cle.com>,
James.Bottomley@...senpartnership.com, OWeisse@...ch.edu,
Dhaval Giani <dhaval.giani@...cle.com>,
Junaid Shahid <junaids@...gle.com>, jsbarnes@...gle.com,
chris.hyser@...cle.com, Ben Segall <bsegall@...gle.com>,
Josh Don <joshdon@...gle.com>, Hao Luo <haoluo@...gle.com>,
Tom Lendacky <thomas.lendacky@....com>,
Aubrey Li <aubrey.li@...el.com>,
"Paul E. McKenney" <paulmck@...nel.org>,
Tim Chen <tim.c.chen@...el.com>
Subject: Re: [PATCH -tip 14/32] sched: migration changes for core scheduling
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.li@...ux.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 <jdesfossez@...italocean.com>
>> Signed-off-by: Aubrey Li <aubrey.li@...ux.intel.com>
>> Signed-off-by: Tim Chen <tim.c.chen@...ux.intel.com>
>> Signed-off-by: Vineeth Remanan Pillai <viremana@...ux.microsoft.com>
>> Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.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.
>> }
>>
>> 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.
Thanks,
-Aubrey
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