Date: Sat, 11 Jun 2011 11:32:31 -0700 From: mdf@FreeBSD.org To: Adrian Chadd <adrian@freebsd.org>, freebsd-arch@freebsd.org Subject: Re: [RFC] shipping kernels with default modules? Message-ID: <BANLkTik=z-fb1sDwh0dr4hRWmdhLMWiKdw@mail.gmail.com> In-Reply-To: <20110611171834.GA38142@zim.MIT.EDU> References: <BANLkTin2AwKRT7N6HWqBctJcT72_mR=Otg@mail.gmail.com> <20110611171834.GA38142@zim.MIT.EDU>
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On Sat, Jun 11, 2011 at 10:18 AM, David Schultz <das@freebsd.org> wrote: > On Sat, Jun 11, 2011, Adrian Chadd wrote: >> Hi guys, >> >> Has there been any further thought as of late about shipping kernels >> with modules only by default, rather than monolithic kernels? >> >> I tried this experiment a couple years ago and besides a little >> trickery with ACPI module loading, it worked out fine. >> >> Is there any reason we aren't doing this at the moment? Eg by having a >> default loader modules list populated from the kernel config file? > > I've been doing this for years, and it has come in quite handy. > For instance, when my if_msk gets wedged, the only way to fix it > short of rebooting seems to be reloading the driver. > > One issue, however, is that the boot loader is horrendously slow > at loading modules. =A0(Either that or my BIOS has a braindead int 13h > handler.) =A0Most of these modules aren't actually needed until much > later in the boot process, so a mechanism to load non-essential > modules after the file systems are mounted might provide a good > solution. Indeed, at $WORK we're trying to get shutdown -> restart under 2 minutes. Several seconds of this is moving things *into* the kernel that need to be there (disk drivers), and everything else to a point in init where modules can be loaded in parallel, using the faster disk driver, rather than in serial with slow BIOS handlers. I'm sure some things about our solution will be generally applicable, but I'm not sure there's a obvious answer that works for GENERIC. Any disk driver that could have a root filesystem under it needs to be in the kernel (or, more slowly loaded as a module by the loader). But then there's a need maybe for network drivers in GENERIC to support PXE boot? And as soon as modules aren't loaded by loader or part of kernel, parts of init will break and need fixing, since they previously relied on modules already being loaded... > OS X has an interesting solution, intended to preserve the > flexibility of dynamic modules, while minimizing boot time. > It provides a kextcache utility, which packages the kernel > and all of the needed modules into a single binary for better > locality on disk. =A0Unlike recompiling the kernel, running > kextcache is fast, and the system runs it automatically when > hardware or driver changes necessitate it. This would be interesting -- isn't it essentially a re-link of the kernel + modules? Cheers, matthew
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