linux-kernel - Re: [PATCH] arch: x86: boot: bioscall.S: simplify self-modification of the INT instruction

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Message-ID: <53CE4A41.4020605@zytor.com>
Date:	Tue, 22 Jul 2014 04:25:53 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Klemen Jan Enova <klemen.jan.enova@...il.com>,
	linux-kernel@...r.kernel.org
CC:	mingo@...hat.com, x86@...nel.org
Subject: Re: [PATCH] arch: x86: boot: bioscall.S: simplify self-modification
 of the INT instruction

On 07/22/2014 04:01 AM, Klemen Jan Enova wrote:
> At the start of the intcall function, the %al register is compared to
> 0x3f. If it does not equal 0x3f it is equated to it. Instruction flow
> continues in both cases from the label 1. The comparison is therefore
> unneeded.
> 
> Testing data is appended.
> 
> Signed-off-and-tested-by: Klemen Jan Enova <klemen.jan.enova@...il.com>

NAK.

This is a performance optimization - the SMC takes a substantial penalty
so the write is avoided if necessary.

Also, 3f is a label, not 0x3f.

	-hpa

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