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[Bug ld/11447] New: default section layout should be improved to reduce
From: |
tglek at mozilla dot com |
Subject: |
[Bug ld/11447] New: default section layout should be improved to reduce pagefaults |
Date: |
29 Mar 2010 20:29:31 -0000 |
I graphed pagefaults on firefox startup which showed that there some bonus page
faults caused by the default section order. The main problem is backwards io
which always causes page faults.
For reference click the second rectange in
http://people.mozilla.com/~tglek/startup/systemtap_graphs/visualize.html?#ld_bug/log.txt.html
x-axis is file offset, y-axis is time
Log of the sections being read is in
http://people.mozilla.com/~tglek/startup/systemtap_graphs/ld_bug/report.txt
Fault #1: This likely can't fixed in ld, but mentioning it in case
Going through the log chronologically there the problems are:
.bss is being zeroed which causes copy-on-write io. Then .dynamic is being
read. The fix should be in the dynamic linker to read .dynamic before memset.
This would allow binaries(where distance between .dynamic and .bss is smaller
than the kernel's readhead) to avoid the .bss pagefault. Perhaps .dynamic should
be the last section before .bss?
Alternatively ld could force .bss to point past the end of the file.
Fault #2
.gnu.version* should be in front of .dyn(sym|str)
Fault #3
.dynstr should be in front of .dynsym
Would be nice if .eh_frame* could be in front of .fini, but as far as I can tell
these have to be in different segments.
--
Summary: default section layout should be improved to reduce
pagefaults
Product: binutils
Version: unspecified
Status: NEW
Severity: normal
Priority: P2
Component: ld
AssignedTo: unassigned at sources dot redhat dot com
ReportedBy: tglek at mozilla dot com
CC: bug-binutils at gnu dot org
http://sourceware.org/bugzilla/show_bug.cgi?id=11447
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