linux-kernel - Re: [PATCH 0/8] x86: Disentangle the vdso and clean it up

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Message-ID: <CALCETrXcTwOQLQX0Tx8XgDPaWit9P5ut1p8mDehAcAah9V17wQ@mail.gmail.com>
Date:	Mon, 20 Oct 2014 14:57:28 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
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 <hpa@...or.com> 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?

--Andy
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