Re: rwsem: down_read_unfair() proposal

[David Howells]

Michel Lespinasse <walken@xxxxxxxxxx> wrote:

> and looks like it's doable with the x86 rwsem implementation as well in a
> way that would only involve changes to the rwsem spinlock-protected slow
> paths in lib/rwsem.c .

It's not as easy as it seems.  Once an XADD-based rwsem is contended, you
cannot necessarily tell without looking at the queue whether the rwsem is
currently write-locked or read-locked.

David
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