linux-kernel - Re: [RFC PATCH 0/3] arm64: queued spinlocks and rw-locks

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Date:   Mon, 24 Apr 2017 14:36:23 +0100
From:   Will Deacon <will.deacon@....com>
To:     Adam Wallis <awallis@...eaurora.org>
Cc:     Yury Norov <ynorov@...iumnetworks.com>,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Arnd Bergmann <arnd@...db.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Jan Glauber <jglauber@...ium.com>,
        Ingo Molnar <mingo@...hat.com>, jason.low2@...com
Subject: Re: [RFC PATCH 0/3] arm64: queued spinlocks and rw-locks

On Wed, Apr 12, 2017 at 01:04:55PM -0400, Adam Wallis wrote:
> On 4/10/2017 5:35 PM, Yury Norov wrote:
> > The patch of Jan Glauber enables queued spinlocks on arm64. I rebased it on
> > latest kernel sources, and added a couple of fixes to headers to apply it 
> > smoothly.
> > 
> > Though, locktourture test shows significant performance degradation in the
> > acquisition of rw-lock for read on qemu:
> > 
> >                           Before           After
> > spin_lock-torture:      38957034        37076367         -4.83
> > rw_lock-torture W:       5369471        18971957        253.33
> > rw_lock-torture R:       6413179         3668160        -42.80
> > 
> 
> On our 48 core QDF2400 part, I am seeing huge improvements with these patches on
> the torture tests. The improvements go up even further when I apply Jason Low's
> MCS Spinlock patch: https://lkml.org/lkml/2016/4/20/725

Does the QDF2400 implement the large system extensions? If so, how do the
queued lock implementations compare to the LSE-based ticket locks?

Will