On Thu, Oct 04, 2012 at 10:32:20AM +0000, Arnd Bergmann wrote: > (+Greg) > > On Tuesday 02 October 2012, Bjorn Helgaas wrote: > > > > On Tue, Oct 2, 2012 at 10:36 AM, Arnd Bergmann <a...@arndb.de> wrote: > > > pci_scan_root_bus is __devinit, so iop13xx_scan_bus has to be the > > > same in order to safely call it. This is ok because the function > > > itself is only called from the hwpci->scan callback. > > > > > > WARNING: vmlinux.o(.text+0x10138): Section mismatch in reference from the > > > function iop13xx_scan_bus() to the function > > > .devinit.text:pci_scan_root_bus() > > > The function iop13xx_scan_bus() references > > > the function __devinit pci_scan_root_bus(). > > > This is often because iop13xx_scan_bus lacks a __devinit > > > annotation or the annotation of pci_scan_root_bus is wrong. > > > > With CONFIG_HOTPLUG going away (I think the current state is that it > > is always set to "y"), __devinit will effectively become a no-op, so I > > expect we'll remove it from pci_scan_root_bus(). > > > > Therefore, I would skip this patch and live with the warning a little > > longer. > > Hmm, I'm just trying to get rid of all build time warnings in the defconfigs > right now, and modpost still complains about the section mismatches. I have > a bunch more of these patches, but it would also be fine with me if we can > patch mostpost to ignore these cases. > > I've also redone the analysis that Greg cited in the commit message for > 45f035ab9b8 "CONFIG_HOTPLUG should be always on" > > It is quite hard to disable it these days, and even if you do, it > only saves you about 200 bytes. However, if it is disabled, lots of > bugs show up because it is almost never tested if the option is disabled. > > My test case (ARM omap2plus_defconfig, one of the most common configurations) > shows these size -A differences: > > > > section nohotplug hotplug difference > .head.text 392 392 0 > .text 4829940 4881140 51200 > .rodata 1630360 1633056 2696 > __ksymtab 25720 25720 0 > __ksymtab_gpl 17096 17136 40 > __kcrctab 12860 12860 0 > __kcrctab_gpl 8548 8568 20 > __ksymtab_stri 96427 96509 82 > __init_rodata 0 9800 9800 > __param 2320 2320 0 > __modver 716 364 -352 > .ARM.unwind_idx 160360 160792 432 > .ARM.unwind_tab 24312 24312 0 > .init.text 234632 195688 -38944 > .exit.text 8680 5116 -3564 > .init.proc.info 312 312 0 > .init.arch.info 2964 2964 0 > .init.tagtable 72 72 0 > .init.smpalt 776 776 0 > .init.pv_table 880 880 0 > .init.data 123356 111348 -12008 > .exit.data 0 0 0 > .data..percpu 12928 12928 0 > .data 560160 562688 2528 > .notes 36 36 0 > .bss 5605324 5605580 256 > > total 13359171 13371357 12186 > after boot 13001183 13054521 53338 > > That is over 50kb difference after discarding the init sections, > significantly more than the 200 bytes that Greg found. > The point about lack of testing is still valid of course, and I'm > not saying we need to keep the option around, but it's really > not as obvious as before. An argument in favor of removing the > __devinit logic is that these 50kb is still just 0.4% of the > kernel size. > > For the five ARM defconfig files that actually turn off hotplug, > the absolute numbers are a bit lower, but the percentage is similar. > > This is the amount of space wasted by enabling on CONFIG_HOTPLUG > on them, in bytes after discarding the init sections, and as a > percentage of the vmlinux size: > > at91x40_defconfig 3448 0.27% > edb7211_defconfig 8912 0.41% > footbridge_defconfig 33347 0.97% > fortunet_defconfig 4592 0.25% > pleb_defconfig 7405 0.28% > > Footbridge is the only config among these that enables PCI and USB, so > it has a bunch more drivers that actually have notable functions that > can be discarded.
USB drivers should not be having anything discarded if CONFIG_HOTPLUG is disabled (it shouldn't be disabled for USB systems, unless someone isn't going to plug a USB device into the system after it comes up, which is one of the main confusions here.) As for PCI, that seems like a lot of code getting thrown away, it would be interesting to figure out why that is. My plans are to now start unwinding the CONFIG_HOTPLUG dependancies. If a driver subsystem really does want to throw away sections (like PCI will if CONFIG_PCI_HOTPLUG is not enabled), then it should be able to. But I imagine all of the real savings will be in the bus cores, not the individual drivers, unless they have huge module_init() functions. Thanks for the numbers, I'll look into this more in the coming weeks. greg k-h -- 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/
