Re: [PATCH] sysctl: Allow /proc/sys without sys_sysctl

Andi Kleen
2006-07-12T16:08:32Z

On Wednesday 12 July 2006 17:32, Eric W. Biederman wrote:
> Andi Kleen <ak@suse.de> writes:
>
> >> So it will correctly handle that sysctl being compiled out, and
> >> the fallback to using /proc. The code seems to have been
> >> doing that since it was added to glibc in 2000.
> >
> > Using /proc is extremly slow for this.
>
> How so it is the same code in the kernel. Is open much slower than
> sys_sysctl?

Yes, the VFS adds quite a lot of overhead with its zillions of
locks and other complicated things.

I have also people complaining about /proc/cpuinfo overhead.
>
> > You added significant cost to each program startup.
>
> Not each program only the ones that use pthreads.

In modern glibc it's basically everything

> > I still think it's a good idea to simulate that sysctl and printk
> > the others.
>
> To reduce the noise something like that makes sense. I'm going to
> see if I can get glibc to use uname which should have the same effect.

And still printk for all old binaries? Not a good idea.

You have to check for this case in the printk stub anyways and
if you check for it you can as well emulate it
(with a big fat comment that this won't be done for any other sysctl)

-Andi