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: <871sc0ptue.fsf@concordia.ellerman.id.au>
Date:   Wed, 18 Jul 2018 23:16:25 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Peter Zijlstra <peterz@...radead.org>
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

Michael Ellerman <mpe@...erman.id.au> writes:
> Peter Zijlstra <peterz@...radead.org> writes:
...
>
> I'll do some kernbench runs tomorrow and see if it shows up there.

Finally got some numbers.

The summary is it's in the noise, the average delta is +0.1s (total time
is ~67s, so 0.17%) but the standard deviation is ~0.2s.

So that's probably a real slow down, but it's very minor.

I guess that's not surprising, given kernbench should be spending the
bulk of its time in userspace.

cheers