linux-kernel - Re: [PATCH 22/23] sysctl arm: Remove binary sysctl support

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Message-ID: <m18wedeqqw.fsf@fess.ebiederm.org>
Date:	Tue, 10 Nov 2009 18:31:51 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Arjan van de Ven <arjan@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 22/23] sysctl arm: Remove binary sysctl support

Andi Kleen <andi@...stfloor.org> writes:

>> Can you name one binary sysctl value that gets accessed more
>> than a few times during the execution of a vaguely common
>> application? We're talking about microseconds for typically
>> write-once or read-once settings.
>
> For example shell scripts tend to execute programs quite a lot.
>
>> The question is just how many sysctl values you regard as both
>> common and performance critical.
>
> Very little, I suspect in fact it's only one.

I just took a second look, attempting to figure out how much startup
overhead my sysctl used.  I failed because I don't have a user space
old enough that it calls sysctl. I had to go back all of the way to
glibc-2.4 to find a version of nptl that calls sysctl at startup.
glibc-2.5 on i386 uses uname and all other architectures uses either
assumes smp is true or false without performing a system call.

I don't believe an inuse version of glibc exists that uses sysctl
except the ioperm implementation on arm.  So I can't see how being
a little slower will impact anyone.

Eric
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