linux-kernel - Re: [PATCH 0/2] rwsem: performance enhancements for systems with many cores

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Message-ID: <1371859222.13136.11.camel@buesod1.americas.hpqcorp.net>
Date:	Fri, 21 Jun 2013 17:00:22 -0700
From:	Davidlohr Bueso <davidlohr.bueso@...com>
To:	Tim Chen <tim.c.chen@...ux.intel.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Alex Shi <alex.shi@...el.com>,
	Andi Kleen <andi@...stfloor.org>,
	Michel Lespinasse <walken@...gle.com>,
	Matthew R Wilcox <matthew.r.wilcox@...el.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH 0/2] rwsem: performance enhancements for systems with
 many cores

On Fri, 2013-06-21 at 16:51 -0700, Tim Chen wrote:
> In this patchset, we introduce two optimizations to read write semaphore.
> The first one reduces cache bouncing of the sem->count field
> by doing a pre-read of the sem->count and avoid cmpxchg if possible.
> The second patch introduces similar optimistic spining logic in
> the mutex code for the writer lock acquisition of rw-sem.
> 
> Combining the two patches, in testing by Davidlohr Bueso on aim7 workloads
> on 8 socket 80 cores system, he saw improvements of
> alltests (+14.5%), custom (+17%), disk (+11%), high_systime
> (+5%), shared (+15%) and short (+4%), most of them after around 500
> users when i_mmap was implemented as rwsem.
> 
> Feedbacks on the effectiveness of these tweaks on other workloads
> will be appreciated.

Tim, I was really hoping to send all this in one big bundle. I was doing
some further testing (enabling hyperthreading and some Oracle runs),
fortunately everything looks ok and we are getting actual improvements
on large boxes.

That said, how about I send you my i_mmap rwsem patchset for a v2 of
this patchset?

Thanks,
Davidlohr

> 
> 
> Alex Shi (1):
>   rwsem: check the lock before cpmxchg in down_write_trylock and    
>     rwsem_do_wake
> 
> Tim Chen (1):
>   rwsem: do optimistic spinning for writer lock acquisition
> 
>  Makefile                    |    2 +-
>  include/asm-generic/rwsem.h |    8 +-
>  include/linux/rwsem.h       |    3 +
>  init/Kconfig                |    9 +++
>  kernel/rwsem.c              |   29 +++++++-
>  lib/rwsem.c                 |  169 ++++++++++++++++++++++++++++++++++++++-----
>  6 files changed, 195 insertions(+), 25 deletions(-)
> 


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