Message-ID: <3EBC2996.2040908@zytor.com>
Date: Fri, 09 May 2003 15:20:06 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
Organization: Zytor Communications
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To: Timothy Miller <miller@techsource.com>
CC: Ulrich Drepper <drepper@redhat.com>, linux-kernel@vger.kernel.org
Subject: Re: hammer: MAP_32BIT
References: <3EBB5A44.7070704@redhat.com> <20030509092026.GA11012@averell> <16059.37067.925423.998433@gargle.gargle.HOWL> <20030509113845.GA4586@averell> <b9gr03$42n$1@cesium.transmeta.com> <3EBC0084.4090809@redhat.com> <3EBC15B5.4070604@zytor.com> <3EBC2164.6050605@redhat.com> <3EBC29A5.1050005@techsource.com>
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Timothy Miller wrote:
> 
> If your program is capable of handling an address with more than 32
> bits, what point is there giving a hint?  Either your program can handle
> 64-bit pointers or it cannot.  Any program flexible enough to handle
> either size dynamically would expend enough overhead checking that it
> would be worse than if it just made a hard choice.
>

The purpose is that there is a slight task-switching speed advantage if
the address is in the bottom 4 GB.  Since this affects every process,
and most processes use very little TLS, this is worthwhile.

This is fundamentally due to a K8 design flaw.

	-hpa

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