linux-kernel - Re: [PATCH v2] tools/memory-model: Add extra ordering for locks and remove it for ordinary release/acquire

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Message-ID: <20180716190139.GR2476@hirez.programming.kicks-ass.net>
Date:   Mon, 16 Jul 2018 21:01:39 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Alan Stern <stern@...land.harvard.edu>,
        andrea.parri@...rulasolutions.com,
        Will Deacon <will.deacon@....com>,
        Akira Yokosawa <akiyks@...il.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Daniel Lustig <dlustig@...dia.com>,
        David Howells <dhowells@...hat.com>,
        Jade Alglave <j.alglave@....ac.uk>,
        Luc Maranget <luc.maranget@...ia.fr>,
        Nick Piggin <npiggin@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] tools/memory-model: Add extra ordering for locks and
 remove it for ordinary release/acquire

On Tue, Jul 17, 2018 at 12:40:19AM +1000, Michael Ellerman wrote:
> 
> I guess arguably it's not a very macro benchmark, but we have a
> context_switch benchmark in the tree[1] which we often use to tune
> things, and it degrades badly. It just spins up two threads and has them
> ping-pong using yield.

The one advantage you'd get from putting it in lock() is that you could
do away with smp_mb__after_spinlock().

But yes, I completely forgot about your IO thingy.. those bench results
make me sad :/ a well.