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List:       gentoo-user
Subject:    Re: [gentoo-user] How to determine 'Least Common Denominator' between Xen(Server) Hosts
From:       Paul Hartman <paul.hartman+gentoo () gmail ! com>
Date:       2013-08-15 18:55:11
Message-ID: CAEH5T2NOeNLdgskWgZ6XqeOtZB4dMgUrRhC5tS+eeGootw4fGQ () mail ! gmail ! com
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On Thu, Aug 15, 2013 at 12:41 PM, Kerin Millar <kerframil@fastmail.co.uk> wrote:
>> I use -mtune=native rather than -march=native, that way I can use some
>> advanced processor features if they are available, but my system will
>> still run if moved to a different host.
>
>
> That's not how -mtune works. If -march is unspecified, it will default to
> the lowest common denominator for the platform which prevents the use of any
> distinguished processor features. For an amd64 install, that would be
> "-march=x86-64".
>
> Instead, -mtune affects everything that -march doesn't. Though it doesn't
> affect the instructions that *can* be used, it may effect which of the
> allowed instructions are used and how. For instance, gcc includes processor
> pipeline descriptions for different microarchitectures so as to emit
> instructions in a way that tries to avoid pipeline hazards:

Thanks very much for the clarification, I appreciate it.

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