(+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.
Arnd
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