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Subject: Re: [PATCH] sched/arm64: store cpu topology before
 notify_cpu_starting
To:     Joel Fernandes <joelaf@google.com>
CC:     Vineeth Remanan Pillai <vpillai@digitalocean.com>,
        <aaron.lwe@gmail.com>, <aubrey.intel@gmail.com>,
        <aubrey.li@linux.intel.com>,
        "Cc: Frederic Weisbecker" <fweisbec@gmail.com>,
        Julien Desfossez <jdesfossez@digitalocean.com>,
        "Joel Fernandes (Google)" <joel@joelfernandes.org>,
        Kees Cook <keescook@chromium.org>,
        Greg Kerr <kerrnel@google.com>,
        LKML <linux-kernel@vger.kernel.org>,
        <mgorman@techsingularity.net>, Ingo Molnar <mingo@kernel.org>,
        <naravamudan@digitalocean.com>, <pauld@redhat.com>,
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        Paul Turner <pjt@google.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        <tim.c.chen@linux.intel.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Valentin Schneider <valentin.schneider@arm.com>,
        <xiexiuqi@huawei.com>, <huawei.libin@huawei.com>, <w.f@huawei.com>,
        "chengjian (D)" <cj.chengjian@huawei.com>,
        "wxf.wang@hisilicon.com >> Xuefeng Wang" <wxf.wang@hisilicon.com>
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 <CAJWu+ooyRsFFA13=rqMBCFgf_JeHsOr16-ayuECaQ5Xz48mrqQ@mail.gmail.com>
From:   "chengjian (D)" <cj.chengjian@huawei.com>
Message-ID: <5cf3996f-0a35-1d98-ec11-9247e95e01e6@huawei.com>
Date:   Fri, 10 Apr 2020 21:49:18 +0800
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On 2020/4/10 1:54, Joel Fernandes wrote:
> On Wed, Apr 1, 2020 at 7:27 AM Cheng Jian <cj.chengjian@huawei.com> wrote:
>> when SCHED_CORE enabled, sched_cpu_starting() uses thread_sibling as
>> SMT_MASK to initialize rq->core, but only after store_cpu_topology(),
>> the thread_sibling is ready for use.
>>
>>          notify_cpu_starting()
>>              -> sched_cpu_starting()     # use thread_sibling
>>
>>          store_cpu_topology(cpu)
>>              -> update_siblings_masks    # set thread_sibling
>>
>> Fix this by doing notify_cpu_starting later, just like x86 do.
>>
>> Signed-off-by: Cheng Jian <cj.chengjian@huawei.com>
> Just a high-level question, why does core-scheduling matter on ARM64?
> Is it for HPC workloads?
>
> Thanks,
>
>   - Joel

Hi, Joel

I am analyzing the mainline scheduling patches and find this problem.


ARM has some platforms that support SMT, and provides some emulate

can be used.


Thanks.

--Cheng Jian