linux-kernel - Re: [PATCH] Use uname not sysctl to get the kernel revision

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Date:	Sat, 15 Jul 2006 04:49:55 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Steve Munroe <sjmunroe@...ibm.com>
Cc:	Theodore Tso <tytso@....edu>, libc-alpha@...rceware.org,
	linux-kernel@...r.kernel.org, Andi Kleen <ak@...e.de>,
	akpm@...l.org, Arjan van de Ven <arjan@...radead.org>,
	Ulrich Drepper <drepper@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Randy.Dunlap" <rdunlap@...otime.net>
Subject: Re: [PATCH] Use uname not sysctl to get the kernel revision

> We will need an implementation that will fall back to sys_sysctl for older
> kernels. This is already common practice in glibc. I don't really
> understand the performance concern because it seems to me that
> _is_smp_system() is only called once per process.
> 
> But isn't this the kind of thing that the Aux Vector is for? I like vDSO
> too, but I think it is best deployed for information of a more dynamic
> nature and performance sensitive.

For a simple "is_smp" kind of flag, I would tend to agree with the
above... for more complex NUMA topology and/or cache characteristics,
which is quite a bigger amount of information, I'm not sure it's worth
copying all of that data on every process exec (and making the initial
AT_ parsing slower). Especially since very few processes actually care
about those.

Ben.


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