On Tue, 2014-05-06 at 08:20 -0700, Alexei Starovoitov wrote: > On Tue, May 6, 2014 at 6:34 AM, Tom Zanussi <tom.zanu...@linux.intel.com> > wrote: > > On Tue, 2014-05-06 at 09:25 +0200, Richard Weinberger wrote: > >> On Tue, May 6, 2014 at 12:25 AM, Andi Kleen <a...@firstfloor.org> wrote: > >> > There has been a lot of interest recently to run Linux on very small > >> > systems, > >> > like Quark systems. These may have only 2-4MB memory. They are also > >> > limited > >> > by flash space. > >> > > >> > One problem on these small system is the size of the network stack. > >> > Currently enabling IPv4 costs about 400k in text, which is prohibitive on > >> > a 2MB system, and very expensive with 4MB. > >> > > >> > There were proposals to instead use LWIP in user space. LWIP with > >> > its socket interface comes in at a bit over 100k overhead per > >> > application. > >> > > >> > I maintain that the Linux network stack is actually not that bloated, > >> > it just has a lot of features :-) The goal of this project was to > >> > subset it in a sensible way so that the native kernel stack becomes > >> > competitive with LWIP. > >> > > >> > It turns out that the standard stack has a couple of features that > >> > are not really needed on client systems. Luckily it is also > >> > relatively well modularized, so it becomes possible to stub > >> > out these features at the edge. > >> > > >> > With removing these features we still have a powerful TCP/IP stack, > >> > but one that fits better into small systems. > >> > > >> > It would have been prohibitive to ifdef every optional feature. > >> > This patchkit relies heavily on LTO to effectively remove unused > >> > code. This allows to disable features only at the module boundaries, > >> > and rely on the compiler to drop unreferenced code and data. > >> > > >> > A few features have been also reimplemented in a simpler way. > >> > And I shrank a number of data structures based on CONFIG_BASE_SMALL. > >> > > >> > With these changes I can get a fully featured network stack down > >> > to about 170k with LTO. Without LTO there are also benefits, > >> > but somewhat less. > >> > > >> > There are essentially three sensible configurations: > >> > - Full featured like today. > >> > - Client only subset, but still works with standard distribution > >> > userland. > >> > Remove some obscure features like fastopen, make all tables smaller, > >> > packet socket mmap code, use a simpler routing table, remove > >> > high speed networking features like RPX, XPS, GRO offload. > >> > Disable SNMP, TCP metrics > >> > - Minimal subset for deeply embedded systems that can use special > >> > userland. > >> > Remove rtnetlink (ioctl only), remove ethtool, raw sockets. > >> > > >> > Right now I'm using own Kconfigs for every removed features. I realize > >> > this somewhat increases the compile test matrix. It would be possible > >> > to hide some of the options and select them using higher level > >> > configurations like the ones listed above. I haven't done this > >> > in this version. > >> > > >> > At this point I'm mainly interested in review and comments. > >> > > >> > Git trees: > >> > > >> > git://git.kernel.org/pub/scm/linux/kernel/git/ak/linux-misc net/debloat > >> > Main tree > >> > > >> > git://git.kernel.org/pub/scm/linux/kernel/git/ak/linux-misc > >> > net/debloat-3.14 > >> > 3.14 based tree. > >> > > >> > Thanks to Tom Zanussi for contributions and testing. > >> > >> What kind of userspace do you use on such a small system? > >> It looks like you run kernels without procfs and netlink, so not even > >> ps would work. :) > >> > > > > The microYocto 'distro' I have running with these net-diet patches > > doesn't use a full procfs, but a pared-down version (CONFIG_PROCFS_MIN). > > Keeping ps working is of course essential, and it does that (along with > > a couple other things like /proc/filesystems and /proc/mounts I needed > > to boot): > > > > https://github.com/tzanussi/linux-yocto-micro-3.14/commit/68379432afcfa82ac695d9f02892fcf48ade5ae8 > > > > Anyway all the userspace and kernel bits are available for anyone who > > wants to build it and try it out: > > > > https://github.com/tzanussi/meta-galileo/blob/daisy/meta-galileo/README > > > > It's very much a work-in-progress with a lot of rough edges, but it is a > > fully functional system on real hardware (Galileo board/Quark processor) > > with a usable shell (ps too!) and web server running on a kernel with > > native networking and ~ 750k text size. > > Intel Galileo datasheet says: > - 400MHz 32bit Intel > - 512 KBytes of on-die embedded SRAM > - 256 MByte DRAM, enabled by the firmware by default > > where did 2-4Mbyte restriction come from? >
General 'order-of-magnitude' difference from the typical 'tiny distro' which typically targets about 16MB, so sort of arbitrary, but it's a nice round goal for similar systems I'm sure are coming. Actually, a better goal would be to run only on the 512k SRAM, but let's start with something more achievable for a first cut. > Anyway, with all these hacks you get a half functional kernel with "a > lot of rough edges" 'work-in-progress' see above. > that is likely working only for the given very limited set of applications. > Kernel function profiling can potentially achieve the same thing. > Profile the kernel with the set of apps and then prune all cold > functions out of kernel. Right, and are Profile-Guided-Optimization results now reproduceable? Better change it to Trace-Guided-Optimization. But yeah, for a single-purpose system where it's known exactly what will run for the lifetime of the system, it makes sense to get rid of all the codepaths that will never be hit. > config explosion and LTO is unnecessary. Just some linker hacks. > Obviously such kernel will also be half functional, > but you'll get big reduction in .text that it seems is the goal of this > project. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
