Re: [PATCH 3/6] locking/rwsem: Set lock ownership ASAP

Peter Zijlstra
2015-01-27T17:10:32Z

On Sun, Jan 25, 2015 at 11:36:06PM -0800, Davidlohr Bueso wrote:
> In order to optimize the spinning step, we need to set the lock
> owner as soon as the lock is acquired; after a successful counter
> cmpxchg operation, that is. This is particularly useful as rwsems
> need to set the owner to nil for readers, so there is a greater
> chance of falling out of the spinning. Currently we only set the
> owner much later in the game, in the more generic level -- latency
> can be specially bad when waiting for a node->next pointer when
> releasing the osq in up_write calls.
>
> As such, update the owner inside rwsem_try_write_lock (when the
> lock is obtained after blocking) and rwsem_try_write_lock_unqueued
> (when the lock is obtained while spinning). This requires creating
> a new internal rwsem.h header to share the owner related calls.
>
> Also cleanup some headers for mutex and rwsem.

This is the thing I suggested
lkml.kernel.org/r/20150108103708.GE29390@twins.programming.kicks-ass.net
there right?

Do you have numbers for how much this gained?