Messages in this thread | | | From | Andy Lutomirski <> | Date | Mon, 20 Oct 2014 14:57:28 -0700 | Subject | Re: [PATCH 0/8] x86: Disentangle the vdso and clean it up |
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On Mon, Oct 20, 2014 at 2:41 PM, H. Peter Anvin <hpa@zytor.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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