Re: [PATCH 2/4] locking/qrwlock: Reduce reader/writer to reader lock transfer latency

[Will Deacon]

On Wed, Jul 08, 2015 at 10:52:48AM +0100, Peter Zijlstra wrote:
> On Tue, Jul 07, 2015 at 05:29:50PM -0400, Waiman Long wrote:
> > I prefer the current setting as you won't know if the writer has the
> > lock or not when you take a snapshot of the value of the lock. You
> > need the whole time sequence in this case to figure it out and so will
> > be more prone to error.
> 
> I still need to wake up, but I suspect we need to change
> queue_read_{try,}lock() to use cmpxchg/inc_not_zero like things, which
> is fine for ARM, but not so much for x86.
> 
> So I think I agree with Waiman, but am willing to be shown differently.

That's fine; I just wanted to make sure I wasn't going round the twist!

Will
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