linux-kernel - Re: [PATCH v3 0/8] x86: entry_64.S: always allocate complete "struct pt

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Date:	Wed, 06 Aug 2014 17:07:52 +0200
From:	Denys Vlasenko <dvlasenk@...hat.com>
To:	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Frederic Weisbecker <fweisbec@...il.com>,
	X86 ML <x86@...nel.org>, Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v3 0/8] x86: entry_64.S: always allocate complete "struct
 pt_regs"

On 08/05/2014 10:13 PM, H. Peter Anvin wrote:
> On 08/05/2014 07:52 AM, Denys Vlasenko wrote:
>> Version 3 of the patchset.
>>
>> Please consider applying at least two first patches, they are definitely safe,
>> and the second one fixes a latent bug.
>>
> 
> Please do provide latency measurements.  I highly suspect that they will
> turn out that that this has no significant impact on latency, but we
> need to know for sure.

I ran tests in totally quiescent state (booted in /bin/sh)
on dual Core i7:

vendor_id	: GenuineIntel
cpu family	: 6
model		: 42
model name	: Intel(R) Core(TM) i7-2620M CPU @ 2.70GHz
stepping	: 7
microcode	: 0x29


"timing_test32 20 getpid" command, best time:
old kernel 266.88 ns per getpid syscall
new kernel 265.95 ns per getpid syscall

"timing_test64 20 getpid" command, best time:
old kernel 54.12 ns per getpid syscall
new kernel 54.30 ns per getpid syscall

In both cases, run-to-run test variability is about 2 ns.
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