https://sourceware.org/bugzilla/show_bug.cgi?id=28441
Bug ID: 28441
Summary: [RISCV] ld linker relaxation is really slow
Product: binutils
Version: 2.35
Status: NEW
Severity: normal
Priority: P2
Component: ld
Assignee: unassigned at sourceware dot org
Reporter: wcohen at redhat dot com
Target Milestone: ---
Created attachment 13718
--> https://sourceware.org/bugzilla/attachment.cgi?id=13718&action=edit
perf annotation of riscv_relax_delete_bytes function
After getting perf annotate working for the RISCV
(https://www.spinics.net/lists/linux-perf-users/msg14852.html) I collected perf
data on systemtap being built on a prototype beagle v board to see where it was
spending time. I noticed that the build was spending a very large amount of
time (>90%) in the code of binutils implementing the relaxation
(https://www.sifive.com/blog/all-aboard-part-3-linker-relaxation-in-riscv-toolchain).
This binutils appears to be a Fedora 33 build of the stock
binutils-2.35-18.fc33.riscv64
(http://fedora.riscv.rocks/koji/buildinfo?buildID=192459 ). Below is
beginning of the "perf report --stdio" output:
# To display the perf.data header info, please use --header/--header-only
options.
#
#
# Total Lost Samples: 0
#
# Samples: 5M of event 'task-clock:u'
# Event count (approx.): 1330053000000
#
# Overhead Command Shared Object Symbol
# ........ ............... .........................................
........................................................
#
94.46% ld libbfd-2.35-18.fc33.so [.]
riscv_relax_delete_bytes
1.27% ld libc-2.32.so [.]
_wordcopy_fwd_dest_aligned
0.81% ld libbfd-2.35-18.fc33.so [.]
_bfd_riscv_relax_section.lto_priv.0
0.18% ld libbfd-2.35-18.fc33.so [.]
elf_sort_elf_symbol
0.17% ld libbfd-2.35-18.fc33.so [.]
bfd_elf_final_link
0.16% ld ld.bfd [.]
sha1_process_block
For more detail on riscv_relax_delete_bytes ran and added as an attachment:
perf annotate riscv_relax_delete_bytes --stdio > ~/riscv_relax_delete_bytes.log
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