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Date:   Tue, 9 May 2023 10:57:45 -0400
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Subject: Re: [PATCH 1/1] locking/qspinlock: Fix state-transition changes in
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To:     "Zhuo, Qiuxu" <qiuxu.zhuo@intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>
Cc:     Boqun Feng <boqun.feng@gmail.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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From:   Waiman Long <longman@redhat.com>
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On 5/9/23 02:57, Zhuo, Qiuxu wrote:
> Hi Longman,
>
> OK, so, you are from the point of view of the CPU (the lock word value it read last time)
> doing state transition in the uncontended scenario:
>
>       [1]:  Old lock word value (this CPU read it last time) ---> New lock word value
>
> I'm from the point of view of the current lock word possible value that its state is
> transited to the new lock word possible value (I don't think I'm the only one from
> this point of view when reading the qspinlock code ;-).
>
>       [2]: Current lock word possible value ---> New lock word possible value
>
> I'm fine to keep the view of [1] in the current code and get [2] as the backup.
> I'll send out a v2 with just two minor comments' fixes.

The purpose of those transition flow charts is to help understand what 
the code is doing. So they should reflect the running CPU point of view. 
If you want to show what all the possible values can be, you have to 
explicitly state that to avoid the confusion.

Thanks,
Longman