Message-ID: <1371859222.13136.11.camel@buesod1.americas.hpqcorp.net>
Subject: Re: [PATCH 0/2] rwsem: performance enhancements for systems with
 many cores
From: Davidlohr Bueso <davidlohr.bueso@hp.com>
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>,
        Matthew R Wilcox <matthew.r.wilcox@intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Rik van Riel <riel@redhat.com>, linux-kernel@vger.kernel.org,
        linux-mm <linux-mm@kvack.org>
Date: Fri, 21 Jun 2013 17:00:22 -0700
In-Reply-To: <1371858691.22432.3.camel@schen9-DESK>
References: <1371858691.22432.3.camel@schen9-DESK>
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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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