On Fri, Feb 15, 2019 at 01:58:34PM -0500, Waiman Long wrote:

On 02/15/2019 01:40 PM, Will Deacon wrote:

quoted

On Thu, Feb 14, 2019 at 11:37:15AM +0100, Peter Zijlstra wrote:

quoted

On Wed, Feb 13, 2019 at 05:00:14PM -0500, Waiman Long wrote:

quoted

v4:
 - Remove rwsem-spinlock.c and make all archs use rwsem-xadd.c.

v3:
 - Optimize __down_read_trylock() for the uncontended case as suggested
   by Linus.

v2:
 - Add patch 2 to optimize __down_read_trylock() as suggested by PeterZ.
 - Update performance test data in patch 1.

The goal of this patchset is to remove the architecture specific files
for rwsem-xadd to make it easer to add enhancements in the later rwsem
patches. It also removes the legacy rwsem-spinlock.c file and make all
the architectures use one single implementation of rwsem - rwsem-xadd.c.

Waiman Long (3):
  locking/rwsem: Remove arch specific rwsem files
  locking/rwsem: Remove rwsem-spinlock.c & use rwsem-xadd.c for all
    archs
  locking/rwsem: Optimize down_read_trylock()

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

with the caveat that I'm happy to exchange patch 3 back to my earlier
suggestion in case Will expesses concerns wrt the ARM64 performance of
Linus' suggestion.

Right, the current proposal doesn't work well for us, unfortunately. Which
was your earlier suggestion?

Will

In my posting yesterday, I showed that most of the trylocks done were
actually uncontended. Assuming that pattern hold for the most of the
workloads, it will not that bad after all.

That's fair enough; if you're going to sit in a tight trylock() loop like the
benchmark does, then you're much better off just calling lock() if you care
at all about scalability.

Will