On Thu, Apr 27, 2023 at 11:21:28AM +0200, Thibaut wrote: > > > Le 27 avr. 2023 à 02:11, Elliott Mitchell <ehem+open...@m5p.com> a écrit : > > > > On Thu, Apr 27, 2023 at 12:50:52AM +0200, Stefan Lippers-Hollmann wrote: > >> On 2023-04-19, Elliott Mitchell wrote: > >>> Direct Rendering Manager is mainly for running X (possibly Wayland > >>> too). As OpenWRT is meant for networking devices, there is no need > >>> for the support to be present. > >> > >> That is only partially true, the Linux kernel is making a strong push > >> away from deprecated (FB_*) graphics drivers to DRM based ones, with > >> kernel based mode setting this is getting more (any) attention for > >> console support as well. Even without getting anywhere near X/ Wayland, > >> there is more than just a 80x25 tty on real hardware (and even VMs). > > > > Real x86 hardware often has the capability to use a serial port as > > console. The conventional UEFI implementation fully supports this use > > case. I can well believe a number of manufacturers disabling the > > functionality though. > > > > VMs *can* have more than a 80x25 tty. By the time you're getting to 4 > > or more VMs you should be thinking about disabling the functionality due > > to the heavy overhead (unless the OS in the VM doesn't support serial > > consoles). > > You seem to assume that x86 is only/mainly run on VMs. > That is not necessarily the case, and I see no reason to degrade device > support that way.
Okay, as already stated there are at least two solutions to this. 1> Turn most functionality into modules and include support for runtime loading of kernel modules. 2> Create more kernel variants for OpenWRT/x86. > Would you mind documenting the measurable gains from your changes, so we have > some metric to assess their relevance? > I had suspected as much, but fully disabling ISA DMA didn't directly have much impact (less than 4195 byte reduction). I was already guessing most of the gain was CONFIG_ISA=n, but hoped purging ISA DMA might squeeze out a bit more. Removing AGP shrunk vmlinux.bin by 4KB. Since the kernel is a multiple of page size, this means a reduction of 1-8191 bytes. This though may have translated into a larger impact when CONFIG_DRM was set to no. Setting CONFIG_DRM=n resulted in a vmlinux.bin delta of -2203648 bytes. Not quite a 10% reduction in kernel runtime size, but close. Here we have a major impact on kernel size. Removing USB support is certainly inappropriate for a desktop build, but appropriate for something using a serial console (some types of VM). That has a delta of -2117632 bytes. Looks like Hyper-V support is a pig. I'm merely going from the size of handy distribution modules, but appears to need ~1MB of memory. Again going by handy distribution modules, the Fusion MPT used by VMware is closer to ~350KB (not including the need for the SCSI layer). Xen meanwhile is ~200KB total. -- (\___(\___(\______ --=> 8-) EHM <=-- ______/)___/)___/) \BS ( | ehem+sig...@m5p.com PGP 87145445 | ) / \_CS\ | _____ -O #include <stddisclaimer.h> O- _____ | / _/ 8A19\___\_|_/58D2 7E3D DDF4 7BA6 <-PGP-> 41D1 B375 37D0 8714\_|_/___/5445 _______________________________________________ openwrt-devel mailing list openwrt-devel@lists.openwrt.org https://lists.openwrt.org/mailman/listinfo/openwrt-devel
