linux-kernel - Re: [PATCH] x86_64: check if Tom2 is enabled

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Message-ID: <4794E130.2090402@zytor.com>
Date:	Mon, 21 Jan 2008 10:15:12 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Cyrill Gorcunov <gorcunov@...il.com>
CC:	Andi Kleen <ak@...e.de>, Yinghai Lu <Yinghai.Lu@....com>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Jesse Barnes <jesse.barnes@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] x86_64: check if Tom2 is enabled

Cyrill Gorcunov wrote:
> [Andi Kleen - Mon, Jan 21, 2008 at 07:03:27PM +0100]
> | 
> | > is it possible to change 'l' and 'h' to 'low' and 'high'?
> | > 'cause 'l' does look like '1' (one) number...
> | 
> | It would be fine for me for someone to implement safe_rdtscll() and get rid
> | of l and h everywhere. IMHO all the l and h accesses of MSRs are just harder
> | to read and error prone over the ll 64bit variants.
> | 
> | But I didn't want to add it just for this.
> | 
> 
> clear enough, thanks
> 

Actually, I think it depends on the specific MSR - some use the halves 
for different data, whereas others treat it as a large 64-bit object.

Ironically enough, the way the MSR interfaces were carried into the 
64-bit world makes the situation worse on 64 bits; edx:eax is the common 
way to represent a 64-bit value on 32 bits.

	-hpa
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