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

[ebiederm@xmission.com (Eric W. Biederman)]

Ulrich Drepper <drepper@redhat.com> writes:

> Eric W. Biederman wrote:
>> But uname is noticeably faster than sysctl and uname is more portable
>> across linux flavors.  So updating the glibc pthread code to use
>> uname looks like the right way to implement is_smp_system. 
>
> This is (was?) not the universal through.  We used uname at some point
> but then I did some profiling and sysctl turned out to be faster.

I track the code bask as far as I could and back to about 2000 in
pthread.c when the code was introduced it always used sys_sysctl.

> If the reverse is true now I can certainly look into changing this but
> the evidence and ideally has to be there.  The simplicity of the uname
> code should mean that it's faster.

The evidence and ideally what has to be there?

> In a year or two I'll remove the test anyway.  By then there will likely
> not be any UP kernels on reasonable machines anymore and I can drop all
> the conditional code.

Well there are embedded targets but I guess uclibc takes care of them.

Unless a darn good reason for keeping it is found, sys_sysctl won't be
in the kernel several months from now.  And uname is faster by a large
margin than /proc.

Right now because there has been a deprecated note in
"include/linux/sysctl.h" since 2003 people currently feel fine with
letting sys_sysctl code bit rot.  I am trying to resolve that
situation most likely by just updating the few stray pieces of user
space that care and then cutting out that chunk of kernel code.

Eric


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