linux-kernel - Re: [PATCH 2/2] KVM: selftests: Use getcpu() instead of sched_getcpu() in rseq

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Message-ID: <2f8f9062-3e89-7a09-02c4-ab1b2dc07356@redhat.com>
Date:   Wed, 10 Aug 2022 10:45:50 +1000
From:   Gavin Shan <gshan@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Florian Weimer <fweimer@...hat.com>, kvmarm@...ts.cs.columbia.edu,
        kvm@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org, pbonzini@...hat.com, maz@...nel.org,
        oliver.upton@...ux.dev, andrew.jones@...ux.dev,
        mathieu.desnoyers@...icios.com, yihyu@...hat.com,
        shan.gavin@...il.com
Subject: Re: [PATCH 2/2] KVM: selftests: Use getcpu() instead of
 sched_getcpu() in rseq_test

On 8/10/22 6:53 AM, Sean Christopherson wrote:
> On Tue, Aug 09, 2022, Gavin Shan wrote:
>> On 8/9/22 5:17 PM, Florian Weimer wrote:
>>> * Florian Weimer:
>>>
>>>> * Gavin Shan:
>>>>
>>>>> sched_getcpu() is glibc dependent and it can simply return the CPU
>>>>> ID from the registered rseq information, as Florian Weimer pointed.
>>>>> In this case, it's pointless to compare the return value from
>>>>> sched_getcpu() and that fetched from the registered rseq information.
>>>>>
>>>>> Fix the issue by replacing sched_getcpu() with getcpu(), as Florian
>>>>> suggested. The comments are modified accordingly.
>>>>
>>>> Note that getcpu was added in glibc 2.29, so perhaps you need to perform
>>>> a direct system call?
>>>
>>> One more thing: syscall(__NR_getcpu) also has the advantage that it
>>> wouldn't have to be changed again if node IDs become available via rseq
>>> and getcpu is implemented using that.
>>>
>>> Thanks,
>>> Florian
>>>
>>
>> Thanks, Florian. It makes sense to me to use syscall(__NR_getcpu) in
>> next revision. Thanks for your quick review :)
> 
> +1, and definitely add a comment to prevent future "cleanup".
> 

Yep, I will have something like below in next revision:

     /*
      * We have to perform direct system call for getcpu() because it's not
      * available until glic 2.29.
      */

Thanks,
Gavin