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Date: Tue, 6 Jun 2017 12:11:52 -0400
From: "Emilio G. Cota" <cota@braap.org>
Message-ID: <20170606161152.GA6109@flamenco>
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Subject: Re: [Qemu-devel] [PATCH v2 1/3] compiler: define QEMU_CACHELINE_SIZE
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To: Pranith Kumar <bobby.prani@gmail.com>
Cc: qemu-devel <qemu-devel@nongnu.org>, Richard Henderson <rth@twiddle.net>, Alex =?iso-8859-1?Q?Benn=E9e?= <alex.bennee@linaro.org>, Peter Maydell <peter.maydell@linaro.org>, Paolo Bonzini <pbonzini@redhat.com>

On Tue, Jun 06, 2017 at 01:39:45 -0400, Pranith Kumar wrote:
> On Mon, Jun 5, 2017 at 6:49 PM, Emilio G. Cota <cota@braap.org> wrote:
> > This is a constant used as a hint for padding structs to hopefully avoid
> > false cache line sharing.
> >
> > The constant can be set at configure time by defining QEMU_CACHELINE_SIZE
> > via --extra-cflags. If not set there, we try to obtain the value from
> > the machine running the configure script. If we fail, we default to
> > reasonable values, i.e. 128 bytes for ppc64 and 64 bytes for all others.
(snip)
> Is there any reason not to use sysconf(_SC_LEVEL1_DCACHE_LINESIZE)?

I tried using sysconf, but it doesn't work on the PowerPC machine I have
access to (it returns 0). It might be a machine-specific thing though-I
don't know. Here's the machine's `uname -a':
  Linux gcc2-power8.osuosl.org 3.10.0-514.10.2.el7.ppc64le #1 SMP Fri Mar \
    3 16:16:38 GMT 2017 ppc64le ppc64le ppc64le GNU/Linux

		E.