[Bug translator/5673] New: tewak kprobe config arrays

[Bug translator/5673] New: tewak kprobe config arrays

[fche at redhat dot com]

Martin points out that .ko's for big wildcard scripts are pretty
big.  probe kernel.function("*") {}  results in a multi-megabyte
.ko whose bulk is the kprobe configuration array.  Let's see if
this can be shrunk.

-- 
           Summary: tewak kprobe config arrays
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: translator
        AssignedTo: systemtap at sources dot redhat dot com
        ReportedBy: fche at redhat dot com


http://sourceware.org/bugzilla/show_bug.cgi?id=5673

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[Bug translator/5673] tweak kprobe config arrays

[fche at redhat dot com]

------- Additional Comments From fche at redhat dot com  2008-01-26 03:15 -------
Some initial findings on the 'probe kernel.function("*") {}' .ko:

Of the .ko space, 90%+ of the data is the stap_dwarf_probe[]
array.  On x86-64, each entry is 200 bytes long, of which
an embedded blank "struct kprobe" is 120, and the union
"struct kretprobe" is 152.  These latter structs need some
independent runtime existence but they don't have to live in
initialized data ==> dynamically allocate them during module_init.

Next, the probe point string, averages ~30 bytes per probe, is
stored in .rodata.str but is not directly compressible.  Perhaps
it is worthwhile breaking up this string field so that link-time
duplicate elimination can work.  Substrings like `kernel.function("'
or `@file/foo.c' could be merged.  (This would mean making the
stap_dwarf_probe struct contain a small array of char*'s instead
of just one.)

Doing these two things should reduce the unnecessary bloat in the
.ko file considerably.  It should no longer be 93%-compressible by
gzip.


-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|tewak kprobe config arrays  |tweak kprobe config arrays


http://sourceware.org/bugzilla/show_bug.cgi?id=5673

------- You are receiving this mail because: -------
You are the assignee for the bug, or are watching the assignee.

[Bug translator/5673] tweak kprobe config arrays

[fche at redhat dot com]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|systemtap at sources dot    |fche at redhat dot com
                   |redhat dot com              |
             Status|NEW                         |ASSIGNED


http://sourceware.org/bugzilla/show_bug.cgi?id=5673

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You are the assignee for the bug, or are watching the assignee.