Re: powerpc allyesconfig / allmodconfig linux-next next-20160729 - next-20160729 build failures

Arnd Bergmann
2016-08-03T18:52:48Z

On Thursday, August 4, 2016 1:37:29 AM CEST Nicholas Piggin wrote:
>
> I've attached what I'm using, which builds and runs for me without
> any work. Your arch obviously has to select the option to use it.
>
> text data bss dec hex filename
> 11196784 1185024 1923820 14305628 da495c vmlinuxppc64.before
> 11187536 1181848 1923176 14292560 da1650 vmlinuxppc64.after
>
> ~9K text saving, ~3K data saving. I assume this comes from fewer
> branch trampolines and toc entries, but haven't verified exactly.

The patch seems to work great, but for me it's getting bigger
(compared to my older patch, mainline allyesconfig doesn't build):

text data bss dec hex filename
51299868 42599559 23362148 117261575 6fd4507 vmlinuxarm.before
51302545 42595015 23361884 117259444 6fd3cb4 vmlinuxarm.after

Most of the difference appears to be in branch trampolines (634 added,
559 removed, 14837 unchanged) as you suspect, but I also see a couple
of symbols show up in vmlinux that were not there before:

-A __crc_dma_noop_ops
-D dma_noop_ops
-R __clz_tab
-r fdt_errtable
-r __kcrctab_dma_noop_ops
-r __kstrtab_dma_noop_ops
-R __ksymtab_dma_noop_ops
-t dma_noop_alloc
-t dma_noop_free
-t dma_noop_map_page
-t dma_noop_mapping_error
-t dma_noop_map_sg
-t dma_noop_supported
-T fdt_add_reservemap_entry
-T fdt_begin_node
-T fdt_create
-T fdt_create_empty_tree
-T fdt_end_node
-T fdt_finish
-T fdt_finish_reservemap
-T fdt_property
-T fdt_resize
-T fdt_strerror
-T find_cpio_data

From my first look, it seems that all of lib/*.o is now getting linked
into vmlinux, while we traditionally leave out everything from lib/
that is not referenced.

I also see a noticeable overhead in link time, the numbers are for
a cache-hot rebuild after a successful allyesconfig build, using a
24-way Opteron@2.5Ghz, just relinking vmlinux:

$ time make skj30 vmlinux # before
real 2m8.092s
user 3m41.008s
sys 0m48.172s

$ time make skj30 vmlinux # after
real 4m10.189s
user 5m43.804s
sys 0m52.988s

That is clearly a very sharp difference. Fortunately for the defconfig
build, the times are much lower, and I see no real difference other
than the noise between subsequent runs:

$ time make skj30 vmlinux # before
real 0m5.415s
user 0m19.716s
sys 0m9.356s
$ time make skj30 vmlinux # before
real 0m9.536s
user 0m21.320s
sys 0m9.224s

$ time make skj30 vmlinux # after
real 0m5.539s
user 0m20.360s
sys 0m9.224s

$ time make skj30 vmlinux # after
real 0m9.138s
user 0m21.932s
sys 0m8.988s

$ time make skj30 vmlinux # after
real 0m5.659s
user 0m20.332s
sys 0m9.620s

Arnd
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