Date: Mon, 27 Aug 2012 15:58:59 +0200
From: Andi Kleen <andi@firstfloor.org>
To: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
Cc: tony.luck@intel.com, andi@firstfloor.org, bp@amd64.org,
        gong.chen@linux.intel.com, ananth@in.ibm.com,
        masbock@linux.vnet.ibm.com, x86@kernel.org,
        linux-kernel@vger.kernel.org, lcm@us.ibm.com, mingo@redhat.com,
        tglx@linutronix.de, linux-edac@vger.kernel.org
Subject: Re: [PATCH 1/2] x86/mce: Pack boolean MCE boot flags into a structure
Message-ID: <20120827135859.GY16230@one.firstfloor.org>
References: <20120827112503.10313.62594.stgit@localhost.localdomain>
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On Mon, Aug 27, 2012 at 04:55:03PM +0530, Naveen N. Rao wrote:
> Many MCE boot flags are boolean in nature, but are declared as integers
> currently. We can pack these into a bitfield to save some space.

Note that this doesn't necessarily save anything because it needs more
code to access, and accesses are more common than the flag

	cmpl  $0,foo(%rip)            7 bytes
        testl $1,foo(%rip)           10 bytes
        bt    $0,foo(%rip)            8 bytes

Even worse for writes. The best you can usually do is to use chars on
x86.

-Andi
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