From: Abel Wu <wuyun.abel@bytedance.com>
To: Yicong Yang <yangyicong@huawei.com>,
Peter Zijlstra <peterz@infradead.org>,
Mel Gorman <mgorman@suse.de>,
Vincent Guittot <vincent.guittot@linaro.org>
Cc: yangyicong@hisilicon.com, Josh Don <joshdon@google.com>,
Chen Yu <yu.c.chen@intel.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/5] sched/fair: ignore SIS_UTIL when has idle core
Date: Thu, 14 Jul 2022 16:00:31 +0800 [thread overview]
Message-ID: <5df03ae2-6c5d-aa38-4a4d-632c0f484140@bytedance.com> (raw)
In-Reply-To: <e8a59a8f-1e0c-2bb6-2d1b-4e76f5c511f5@huawei.com>
On 7/14/22 3:15 PM, Yicong Yang Wrote:
> On 2022/7/14 14:58, Abel Wu wrote:
>>
>> On 7/14/22 2:19 PM, Yicong Yang Wrote:
>>> On 2022/7/12 16:20, Abel Wu wrote:
>>>> When SIS_UTIL is enabled, SIS domain scan will be skipped if
>>>> the LLC is overloaded. Since the overloaded status is checked
>>>> in the load balancing at LLC level, the interval is llc_size
>>>> miliseconds. The duration might be long enough to affect the
>>>> overall system throughput if idle cores are out of reach in
>>>> SIS domain scan.
>>>>
>>>> Signed-off-by: Abel Wu <wuyun.abel@bytedance.com>
>>>> ---
>>>> kernel/sched/fair.c | 15 +++++++++------
>>>> 1 file changed, 9 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>>>> index a78d2e3b9d49..cd758b3616bd 100644
>>>> --- a/kernel/sched/fair.c
>>>> +++ b/kernel/sched/fair.c
>>>> @@ -6392,16 +6392,19 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool
>>>> struct sched_domain *this_sd;
>>>> u64 time = 0;
>>>> - this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc));
>>>> - if (!this_sd)
>>>> - return -1;
>>>> -
>>>> cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
>>>> - if (sched_feat(SIS_PROP) && !has_idle_core) {
>>>> + if (has_idle_core)
>>>> + goto scan;
>>>> +
>>>> + if (sched_feat(SIS_PROP)) {
>>>> u64 avg_cost, avg_idle, span_avg;
>>>> unsigned long now = jiffies;
>>>> + this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc));
>>>> + if (!this_sd)
>>>> + return -1;
>>>> +
>>>
>>> I don't follow the change here. True that this_sd is used only in SIS_PROP, but it seems irrelevant with your
>>> commit. Does the position of this make any performance difference?
>>
>> No, this change doesn't make much difference to performance. Are
>> you suggesting that I should make this a separate patch?
>>
>
> It just makes me think that dereference is unnecessary if this_cpu and target locates in
> the same LLC, since it's already been passed. But since you noticed no difference it may
> have little effect. :)
>
Hmm.. Not exactly. The sched-domains are cpu private, and this_cpu can
be in another LLC than target.
next prev parent reply other threads:[~2022-07-14 8:01 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-12 8:20 [PATCH 0/5] sched/fair: SIS improvements and cleanups Abel Wu
2022-07-12 8:20 ` [PATCH 1/5] sched/fair: ignore SIS_UTIL when has idle core Abel Wu
2022-07-13 3:47 ` Chen Yu
2022-07-13 16:14 ` Abel Wu
2022-07-14 6:19 ` Yicong Yang
2022-07-14 6:58 ` Abel Wu
2022-07-14 7:15 ` Yicong Yang
2022-07-14 8:00 ` Abel Wu [this message]
2022-07-14 8:16 ` Yicong Yang
2022-07-14 8:34 ` Yicong Yang
2022-08-04 9:59 ` Chen Yu
2022-08-15 2:54 ` Abel Wu
2022-08-10 13:50 ` Chen Yu
2022-08-15 2:44 ` Abel Wu
2022-08-29 13:08 ` Mel Gorman
2022-08-29 14:11 ` Abel Wu
2022-08-29 14:56 ` Mel Gorman
2022-09-01 13:08 ` Abel Wu
2022-09-02 4:12 ` Abel Wu
2022-09-02 10:25 ` Mel Gorman
2022-09-05 14:40 ` Abel Wu
2022-09-06 9:57 ` Mel Gorman
2022-09-07 7:27 ` Chen Yu
2022-09-07 8:41 ` Mel Gorman
2022-09-07 7:52 ` Abel Wu
2022-07-12 8:20 ` [PATCH 2/5] sched/fair: default to false in test_idle_cores Abel Wu
2022-08-29 12:36 ` Mel Gorman
2022-07-12 8:20 ` [PATCH 3/5] sched/fair: remove redundant check in select_idle_smt Abel Wu
2022-08-29 12:36 ` Mel Gorman
2022-07-12 8:20 ` [PATCH 4/5] sched/fair: avoid double search on same cpu Abel Wu
2022-08-29 12:36 ` Mel Gorman
2022-07-12 8:20 ` [PATCH 5/5] sched/fair: remove useless check in select_idle_core Abel Wu
2022-08-29 12:37 ` Mel Gorman
2022-08-15 13:31 ` [PATCH 0/5] sched/fair: SIS improvements and cleanups Abel Wu
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