Re: [RFC PATCH-tip v4 07/10] locking/rwsem: Change RWSEM_WAITING_BIAS for better disambiguation
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- To: Waiman Long <waiman.long@xxxxxxx>
- Subject: Re: [RFC PATCH-tip v4 07/10] locking/rwsem: Change RWSEM_WAITING_BIAS for better disambiguation
- From: Wanpeng Li <kernellwp@xxxxxxxxx>
- Date: Mon, 22 Aug 2016 10:15:28 +0800
- Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, "the arch/x86 maintainers" <x86@xxxxxxxxxx>, linux-alpha@xxxxxxxxxxxxxxx, linux-ia64@xxxxxxxxxxxxxxx, linux-s390 <linux-s390@xxxxxxxxxxxxxxx>, linux-arch@xxxxxxxxxxxxxxx, linux-doc@xxxxxxxxxxxxxxx, Davidlohr Bueso <dave@xxxxxxxxxxxx>, Jason Low <jason.low2@xxxxxx>, Dave Chinner <david@xxxxxxxxxxxxx>, Jonathan Corbet <corbet@xxxxxxx>, Scott J Norton <scott.norton@xxxxxxx>, Douglas Hatch <doug.hatch@xxxxxxx>
- In-reply-to: <57B73225.7020303@hpe.com>
- References: <1471554672-38662-1-git-send-email-Waiman.Long@hpe.com> <1471554672-38662-8-git-send-email-Waiman.Long@hpe.com> <CANRm+CzfQFHDZDdBc+WxSkFPaE6x=b+PGBeEnnAqgmjDi=1DDA@mail.gmail.com> <57B73225.7020303@hpe.com>
2016-08-20 0:21 GMT+08:00 Waiman Long <waiman.long@xxxxxxx>:
> On 08/19/2016 01:57 AM, Wanpeng Li wrote:
>>
>> 2016-08-19 5:11 GMT+08:00 Waiman Long<Waiman.Long@xxxxxxx>:
>>>
>>> When the count value is in between 0 and RWSEM_WAITING_BIAS, there
>>> are 2 possibilities.
>>> Either a writer is present and there is no waiter
>>
>> count = 0xffff0001
>>
>>> or there are waiters and readers. There is no easy way to
>>
>> count = 0xffff000X
>>
>> However, RWSEM_WAITING_BIAS is equal to 0xffff0000, so both these two
>> cases are beyond RWSEM_WAITING_BIAS, right?
>>
>> Regards,
>> Wanpeng Li
>
>
> Perhaps I should make it clear that I am talking from a signed quantity
> point of view (it is an atomic_long_t). So
>
> RWSEM_WAITING_BIAS < RWSEM_ACTIVE_WRITE_BIAS < 0
>
> Hope this clarify your question.
Yeah, thank you. :)
Regards,
Wanpeng Li
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