Gentoo Archives: gentoo-user

From: Bruce Hill <daddy@×××××××××××××××××××××.com>
To: gentoo-user@l.g.o
Subject: Re: [gentoo-user] How to determine 'Least Common Denominator' between Xen(Server) Hosts
Date: Wed, 14 Aug 2013 12:15:28
Message-Id: 20130814121516.GH24244@server
In Reply to: [gentoo-user] How to determine 'Least Common Denominator' between Xen(Server) Hosts by Pandu Poluan
1 On Wed, Aug 14, 2013 at 12:18:41PM +0700, Pandu Poluan wrote:
2 > Hello list!
3 >
4 > My company has 2 HP DL585 G5 servers and 5 Dell R... something servers. All
5 > using AMD processors. They currently are acting as XenServer hosts.
6 >
7 > How do I determine the 'least common denominator' for Gentoo VMs (running
8 > as XenServer guests), especially for gcc flags?
9 >
10 > I know that the (theoretical) best performance is to use -march=native ,
11 > but since the processors of the HP servers are not exactly the same as the
12 > Dell's, I'm concerned that compiling with -march=native will render the VMs
13 > unable to migrate between the different hosts.
14 >
15 > Note: Yes I know the HP servers are much older than the Dell ones, but if I
16 > go -march=native then perform an emerge when the guest is on the Dell host,
17 > the guest VM might not be able to migrate to the older HPs.
19 To check what options CFLAGS set as -march=native would use:
20 gcc -march=native -E -v - </dev/null 2>&1 | sed -n 's/.* -v - //p'
21 (the first thing in the output is what CPU -march=native would enable)
23 Then you can run:
24 diff -u <(gcc -Q --help=target) <(gcc -march=native -Q --help=target)
25 to display target-specific options, versus native ones.
27 Assuming the 2 HP servers are identical, and the 5 Dell servers are identical,
28 you then only need to get the commonality of two processors (HP and Dell).
29 Since they're both AMD, you should have a good set of common features to help
30 you determine that "least common denominator", or target.
31 --
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Subject Author
Re: [gentoo-user] How to determine 'Least Common Denominator' between Xen(Server) Hosts Kerin Millar <kerframil@×××××××××××.uk>