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Date: Mon, 24 Jun 2013 10:46:45 +0200
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 2/2] rwsem: do optimistic spinning for writer lock
 acquisition
Message-ID: <20130624084645.GL28407@twins.programming.kicks-ass.net>
References: <cover.1371855277.git.tim.c.chen@linux.intel.com>
 <1371858700.22432.5.camel@schen9-DESK>
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To: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Ingo Molnar <mingo@elte.hu>, Andrew Morton <akpm@linux-foundation.org>, Andrea Arcangeli <aarcange@redhat.com>, Alex Shi <alex.shi@intel.com>, Andi Kleen <andi@firstfloor.org>, Michel Lespinasse <walken@google.com>, Davidlohr Bueso <davidlohr.bueso@hp.com>, Matthew R Wilcox <matthew.r.wilcox@intel.com>, Dave Hansen <dave.hansen@intel.com>, Rik van Riel <riel@redhat.com>, linux-kernel@vger.kernel.org, linux-mm <linux-mm@kvack.org>

On Fri, Jun 21, 2013 at 04:51:40PM -0700, Tim Chen wrote:
> Introduce in this patch optimistic spinning for writer lock
> acquisition in read write semaphore.  The logic is
> similar to the optimistic spinning in mutex but without
> the MCS lock queueing of the spinner.  This provides a
> better chance for a writer to acquire the lock before
> being we block it and put it to sleep.
> 
> Disabling of pre-emption during optimistic spinning
> was suggested by Davidlohr Bueso.  It
> improved performance of aim7 for his test suite.
> 
> Combined with the patch to avoid unnecesary cmpxchg,
> 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 he implemented i_mmap as rwsem.
> 
> Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
> ---
>  Makefile              |    2 +-
>  include/linux/rwsem.h |    3 +
>  init/Kconfig          |    9 +++
>  kernel/rwsem.c        |   29 +++++++++-
>  lib/rwsem.c           |  148 +++++++++++++++++++++++++++++++++++++++++++++----
>  5 files changed, 178 insertions(+), 13 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index 49aa84b..7d1ef64 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1,7 +1,7 @@
>  VERSION = 3
>  PATCHLEVEL = 10
>  SUBLEVEL = 0
> -EXTRAVERSION = -rc4
> +EXTRAVERSION = -rc4-optspin4
>  NAME = Unicycling Gorilla
>  
>  # *DOCUMENTATION*

I'm fairly sure we don't want to commit this hunk ;-)

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