linux-kernel - Re: [PATCH 4/5] x86: entry_64.S: always allocate complete "struct pt

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Message-ID: <CALCETrU2ZUKorqUzFZUJ7TRSUL9fS9yBT+SiSH_Zsz6bHcE36A@mail.gmail.com>
Date:	Sat, 2 Aug 2014 14:14:50 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Denys Vlasenko <vda.linux@...glemail.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	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 4/5] x86: entry_64.S: always allocate complete "struct pt_regs"

On Fri, Aug 1, 2014 at 3:13 PM, H. Peter Anvin <hpa@...or.com> wrote:
> On 08/01/2014 03:11 PM, Denys Vlasenko wrote:
>>>
>>> Could you please try to see if there is a measurable change in the
>>> latency of a trivial syscall?
>>
>> Will do.
>> Something along the lines of "how long does it take to execute two
>> gazillions of getppid()?"
>>
>
> Something like that, yes, but you have to run enough data points so you
> can determine if the difference is statistically significant or just noise.

Denys, if you want to avoid five minutes of programming, you can build this:

https://gitorious.org/linux-test-utils/linux-clock-tests/

and run timing_test_64 10 getpid

It doesn't do real statistics, but it seems to get quite stable results.

--Andy
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