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Date:	Mon, 20 Oct 2014 14:57:28 -0700
From:	Andy Lutomirski <>
To:	"H. Peter Anvin" <>
Cc:	Thomas Gleixner <>,
	Ingo Molnar <>, X86 ML <>,
	"" <>
Subject: Re: [PATCH 0/8] x86: Disentangle the vdso and clean it up

On Mon, Oct 20, 2014 at 2:41 PM, H. Peter Anvin <> wrote:
> On 09/23/2014 10:50 AM, Andy Lutomirski wrote:
>> Patch 8 removes the vvar that selects the getcpu mode.  That vvar
>> has been unnecessary for a couple of years, ever since alternative
>> patching has worked in the vdso.
> Is there any fundamental reason to not always use LSL at this point?

No, other than aesthetics.

Crappy timings on my dev box:

rdtscp: 18ns (and slowdown of nearly insns because it's like lfence or
mfence IIRC)

lsl: 15ns

just for fun, lsl of an out of bounds descriptor: 46ns

lsl is also nice because it works even if CR4.TSD is set.

I know I probably shouldn't say this, but sgdt is even faster (<8ns)

Should I send a replacement for patch 8 or should I let you merge 1-7
and fold this into the followup series?

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