Messages in this thread |  | | Date | Mon, 20 Apr 2015 20:28:32 +0200 | From | Ingo Molnar <> | Subject | Re: [GIT RFC PULL rcu/urgent] Prevent Kconfig from asking pointless questions |
| |
* Steven Rostedt <rostedt@goodmis.org> wrote:
> On Mon, 20 Apr 2015 20:09:04 +0200 > Ingo Molnar <mingo@kernel.org> wrote: > > > > So the disadvantage is that if a boot default is wrong, we'll hear > > about it eventually and can fix/improve it. > > > > If a sysctl knob is wrong, people will just 'tune' it and forget > > to propagate it to the kernel proper (why should they). > > My fear is that there is no one true value. [...]
Do we know that?
> [...] One person complains about it, we change it, then someone else > complains about the new value. That would be even worse.
At that point we can still add a sysctl, if valid arguments are offered.
> > Which is fine for something like ftrace and other ad-hoc > > instrumentation that is generally very fine tuned to a given bug > > or given piece of hardware, but for something like the RCU > > implementation of the kernel - even if it's just a RT side thought > > of it - I'm not so sure about it. > > I would argue than every case is different, and only the sysadmin > would know the right value. Thus, just set it to one, and if that's > not good enough, then the sysadmins can change it to their needs.
Well, we had really bad experience with sysctls in the past, in particular in the VM: with various settings exposed and distros 'tuning' them - sometimes radically changing the way the system worked, confusing everyone involved.
So I'm in general opposed to sysctls for core kernel behavior - except for cases where we don't know better.
Instrumentation - especially instrumentation that should have been implemented mostly in user-space, like ftrace ;-) - is another special case that should stay as flexible as possible via sysctls, obviously.
Thanks,
Ingo
|  |