Re: [PATCH RFC 1/2] qrwlock: A queue read/write lock implementation

["George Spelvin" <linux@horizon.com>]

> What I have in mind is to have 2 separate rwlock initializers - one for 
> fair and one for reader-bias behavior. So the lock owners can decide 
> what behavior do they want with a one line change.

That's definitely a nicer patch, if it will work.  I was imagining that,
even for a single (type of) lock, only a few uses require reader bias
(because they might be recursive, or are in an interrupt), but you'd
want most read_lock sites to be fair.

Deciding on a per-lock basis means that one potentially recursive call
means you can't use fair queueing anywhere.

I was hoping that the number of necessary unfair calls would
be small enough that making the read_lock default fair and
only marking the unfair call sites would be enough.

But I don't really know until doing a survey of the calls.