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

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Date:	Fri, 21 Jun 2013 17:25:16 -0700
From:	Michel Lespinasse <walken@...gle.com>
To:	Davidlohr Bueso <davidlohr.bueso@...com>
Cc:	Tim Chen <tim.c.chen@...ux.intel.com>, 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>,
	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, Jun 21, 2013 at 5:00 PM, Davidlohr Bueso <davidlohr.bueso@...com> wrote:
> 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?

I'm a bit confused about the state of these patchsets - it looks like
I'm only copied into half of the conversations. Should I wait for a v2
here, or should I hunt down for Alex's version of things, or... ?

-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
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