linux-kernel - Re: [RFC PATCH-tip v4 07/10] locking/rwsem: Change RWSEM_WAITING

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Message-ID: <CANRm+CzfQFHDZDdBc+WxSkFPaE6x=b+PGBeEnnAqgmjDi=1DDA@mail.gmail.com>
Date:   Fri, 19 Aug 2016 13:57:49 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Waiman Long <Waiman.Long@....com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        linux-alpha@...r.kernel.org, linux-ia64@...r.kernel.org,
        linux-s390 <linux-s390@...r.kernel.org>,
        linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
        Davidlohr Bueso <dave@...olabs.net>,
        Jason Low <jason.low2@...com>,
        Dave Chinner <david@...morbit.com>,
        Jonathan Corbet <corbet@....net>,
        Scott J Norton <scott.norton@....com>,
        Douglas Hatch <doug.hatch@....com>
Subject: Re: [RFC PATCH-tip v4 07/10] locking/rwsem: Change RWSEM_WAITING_BIAS
 for better disambiguation

2016-08-19 5:11 GMT+08:00 Waiman Long <Waiman.Long@....com>:
> 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