Date: Mon, 7 Sep 2015 16:52:19 -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: <D2DAE86C-F7A5-46C7-95B5-42927927AB5A@bsdimp.com> In-Reply-To: <20150907224808.GC1778@garage.freebsd.pl> References: <EC6B1705-8189-436C-9E47-20E8A4AF8488@bsdimp.com> <20150907212943.GB1778@garage.freebsd.pl> <CANCZdfqNE9z6bfDzcadLVYJkKpXyzURZZ9jAYs5hF4TZ377Cvw@mail.gmail.com> <20150907224808.GC1778@garage.freebsd.pl>
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[-- Attachment #1 --] > On Sep 7, 2015, at 4:48 PM, Pawel Jakub Dawidek <pjd@FreeBSD.org> wrote: > > On Mon, Sep 07, 2015 at 04:18:25PM -0600, Warner Losh wrote: >> 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’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. >> >> >> 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. > > Do you have some numbers handy? I'd be interested in seeing how much > performance drop there is when you have INVARIANTS compiled in, but > debug.invariants set to 0. I don’t have any direct numbers, but the belief is that we’ll see between 10-20% drop in our peak throughput with an INVARIANTS kernel. Warner [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Comment: GPGTools - https://gpgtools.org iQIcBAEBCgAGBQJV7hUkAAoJEGwc0Sh9sBEAhTwP/jDWBBk+C0AEiTjKaqtE2AM7 v0AsyL/1dbgxihybK728U1EOE9PeQuaXqfwrlQ1nCcdH06snq62iagiHibyksGAa RZrLZRv9MYDq0nvVf42FFdRRbwAAimwLumzCEJtfyxgA3pcRd4EnLxZA6f6kwoga WzJho1gI5qK6eMwzZx+uz0K5dWgXQJSWpJzTiFkHyOQV6skmpZcxIVQDnQF1sAuA XAZlx3XqNCEi8uzjVgf5XytkCVNp6tB9Fjc82gRM249QVLSBkQIeSu8IDjk8xeEk xNtg3BM3G8TwjeRmHDGM2c27pkaaK1cWe/tBM3fyqUOZuxSLDc/lzkj11Jgntuek krdRShitMRUgDsVtUlAemroB5fg9nONzuRI91tDraArQocE1b2dZARAw0/9jWXsp OnsXH2z4NDalEY2Do6kZy65G8KpRC2dVHRpmquU/yUog6HhdOS/afglfwYvXY/zt Jff5nmk1iQvT4KyryZIPfvMmf7disJlf0cuWoUMVDVPZnx5NRHxNcekqs1i0Asbo Bz6sE5zyCSsXEXi7X32Xp3v1XVgUukiDGREbw8w6ejSz/32xaq8gpUJLCpxTvdxb jfmxB5KhOPtDAvUB6wh9MOKIZr2bbavXmwhZut3GyuunALzXaYMOtxr1jejdk+zn HiHdh1+w6ASlSZjZCnnq =xBM0 -----END PGP SIGNATURE-----help
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