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

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Message-ID: <CALCETrW8mvr4LaFWuDoz+L9XCQFrzb0Fa1E9vuMTEv-YunLsFg@mail.gmail.com>
Date:	Sat, 2 Aug 2014 14:38:56 -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 Sat, Aug 2, 2014 at 2:23 PM, H. Peter Anvin <hpa@...or.com> wrote:
> It would be nice to automate running a T-test on it.

I'll see if I can do something like that.  Using the t statistic seems
like overkill here, though -- timing_test_64 runs millions of
iterations, so even if I batch them, I'll end up with n ~ 1000 (or
even larger), at which point plain old Gaussians should be fine.

--Andy

>
> On August 2, 2014 2:14:50 PM PDT, Andy Lutomirski <luto@...capital.net> wrote:
>>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
>
> --
> Sent from my mobile phone.  Please pardon brevity and lack of formatting.



-- 
Andy Lutomirski
AMA Capital Management, LLC
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