Date: Mon, 7 Sep 2015 16:18:25 -0600 From: Warner Losh <imp@bsdimp.com> To: Pawel Jakub Dawidek <pjd@freebsd.org> Cc: "freebsd-arch@freebsd.org" <arch@freebsd.org> Subject: Re: exporting INVARIANTS easily Message-ID: <CANCZdfqNE9z6bfDzcadLVYJkKpXyzURZZ9jAYs5hF4TZ377Cvw@mail.gmail.com> In-Reply-To: <20150907212943.GB1778@garage.freebsd.pl> References: <EC6B1705-8189-436C-9E47-20E8A4AF8488@bsdimp.com> <20150907212943.GB1778@garage.freebsd.pl>
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On Mon, Sep 7, 2015 at 3:29 PM, Pawel Jakub Dawidek <pjd@freebsd.org> wrote= : > 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=E2=80= =99t one > of those > > features. > > > > https://reviews.freebsd.org/D3488 > > > > implements debug.invariants. Please comment. > > > > I=E2=80=99d thought about adding it to the kern.features sysctl, but th= ought > better of it since it > > isn=E2=80=99t 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=E2=80=99t built that way and this won=E2=80=99t reflect that= . There=E2=80=99s 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=E2=80=99t accidentally include INVAR= IANTS > systems > > in the performance number, we=E2=80=99ve adding a key to an internal da= tabase > that=E2=80=99s 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. That's not my goal. And I doubt my employer would run it in their kernel config because it costs too much in bandwidth when we're streaming all that video people binge watch. Warner
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