Messages in this thread | | | Date | Tue, 21 Jan 2014 11:16:03 -0500 | From | Waiman Long <> | Subject | Re: [PATCH v8 4/4] qrwlock: Use smp_store_release() in write_unlock() |
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On 01/21/2014 10:41 AM, Peter Zijlstra wrote: > On Tue, Jan 21, 2014 at 10:02:06AM -0500, Waiman Long wrote: >> My latest v9 series of qrwlock patch will automatically adapt to the lack of >> atomic byte access by using an atomic integer instruction instead. So the >> new series should work for pre-EV56 Alpha, it is just a bit less efficient >> in this case. > See my other email; I don't think you can do that without also changing > the implementation of the queue_read_{try}lock() functions. > > Without those changes you can have transient values in your 'read-count' > part of the word and a full word write will wreck things.
I don't see any problem with my current logic. If a writer has the write lock, the writer byte has to have a value of 0xff. So atomically subtracting 0xff from it will guarantee that the writer byte will become zero, which is the same as assigning a zero value to that byte. The only difference is that an atomic subtract instruction will need to be used instead of a simple byte assignment.
Please let me know if there is any flaw in my logic.
-Longman
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