Re: [PATCH -v5][RFC]: mutex: implement adaptive spinning

Gregory Haskins
2009-01-08T03:57:25Z

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Steven Rostedt wrote:
> On Wed, 7 Jan 2009, Gregory Haskins wrote:
>
>> In my defense, the -rt versions of the patches guarantee this is ok
>> based on a little hack:
>>
>
> The -rt versions worry about much more than what the mutex code in
> mainline does. Linus is correct in his arguments. The adaptive mutex (as
> suppose to what -rt has), is only to help aid in preformance. There are a
> lot of races that can happen in mainline version where lock taking may not
> be fifo, or where we might start to schedule when we could have taken the
> lock. These races are not in -rt, but that is because -rt cares about
> these. But mainline cares more about performance over determinism. This
> means that we have to look at the current code that Peter is submitting
> with a different perspective than we do in -rt.
>

Hey Steve,
Understood, and agreed. I only mentioned it because I wanted to clear
the record that I did not (to my knowledge) mess up the protocol design
which first introduced the get/put-task pattern under discussion ;). I
am fairly confident that at least the -rt version does not have any race
conditions such as the one Linus mentioned in the mainline version. I
am not advocating that the full protocol that we use in -rt should be
carried forward, per se or anything like that.

-Greg

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