exporting INVARIANTS easily

[Pawel Jakub Dawidek]

On Wed, Aug 26, 2015 at 11:20:06AM -0600, Warner Losh wrote:
> Greetings,
> 
> Many of the performance eating features are exported via some kind of sysctl, usually
> patterned after the case of witness as debug.foo. INVARIANTS isn’t one of those
> features.
> 
> https://reviews.freebsd.org/D3488
> 
> implements debug.invariants. Please comment.
> 
> I’d thought about adding it to the kern.features sysctl, but thought better of it since it
> isn’t a facility that people can use.
> 
> If you include the kernel config in the kernel, you can get this information via
> 	config -x | grep INVARIANTS
> but not all kernels do that. This is more robust.
> 
> I also know that you can load some modules compiled INVARIANTS when the base
> kernel isn’t built that way and this won’t reflect that. There’s no good want to include
> that information and is an uncommon use case.
> 
> Our use case? We have a raft of test machines. Most run without INVARIANTS since
> we want to characterize the performance of the release under test. Some are running
> INVARIANTS since we want to test the robustness as well, even at the expense of
> some performance. To ensure we don’t accidentally include INVARIANTS systems
> in the performance number, we’ve adding a key to an internal database that’s driven
> off this sysctl.
> 
> Comments?

As long as the ultimate goal is to have INVARIANTS in GENERIC I'm all
for it! I use to run even production machines with INVARIANTS, which was
helpful to catch VirtualBox's kernel memory corruption, but we've moved
to GENERIC since I wanted to use freebsd-update. Having INVARIANTS in
GENERIC would be great.

-- 
Pawel Jakub Dawidek                       http://www.wheelsystems.com
FreeBSD committer                         http://www.FreeBSD.org
Am I Evil? Yes, I Am!                     http://mobter.com
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 819 bytes
Desc: not available
URL: <http://lists.freebsd.org/pipermail/freebsd-arch/attachments/20150907/720e5b4c/attachment.bin>