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Subject: Re: [RFC][PATCH 0/4] arm64:kvm: teach guest sched that VCPUs can be
 preempted
To:     Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        "will@kernel.org" <will@kernel.org>,
        "maz@kernel.org" <maz@kernel.org>
References: <20200721041742.197354-1-sergey.senozhatsky@gmail.com>
 <20200817020310.GA1210848@jagdpanzerIV.localdomain>
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        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "Wanghaibin (D)" <wanghaibin.wang@huawei.com>,
        <yezengruan@huawei.com>
From:   yezengruan <yezengruan@huawei.com>
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Date:   Mon, 17 Aug 2020 20:03:09 +0800
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On 2020/8/17 10:03, Sergey Senozhatsky wrote:
> On (20/07/21 13:17), Sergey Senozhatsky wrote:
>> Hello,
>>
>> 	RFC
>>
>> 	We noticed that in a number of cases when we wake_up_process()
>> on arm64 guest we end up enqueuing that task on a preempted VCPU. The culprit
>> appears to be the fact that arm64 guests are not aware of VCPU preemption
>> as such, so when sched picks up an idle VCPU it always assumes that VCPU
>> is available:
>>
>>       wake_up_process()
>>        try_to_wake_up()
>>         select_task_rq_fair()
>>          available_idle_cpu()
>>           vcpu_is_preempted()    // return false;
>>
>> Which is, obviously, not the case.
>>
>> This RFC patch set adds a simple vcpu_is_preempted() implementation so
>> that scheduler can make better decisions when it search for the idle
>> (v)CPU.
> Hi,
>
> A gentle ping.
>
> 	-ss
> _______________________________________________
> kvmarm mailing list
> kvmarm@lists.cs.columbia.edu
> https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
> .

Hi Sergey,

I have a set of patches similar to yours.

https://lore.kernel.org/lkml/20191226135833.1052-1-yezengruan@huawei.com/