[Bug kprobes/6989] New: kprobe_hash_table is too small for systemtap

[Bug kprobes/6989] New: kprobe_hash_table is too small for systemtap

[mhiramat at redhat dot com]

kprobe_hash_table[] has just 64 entries, and it's too small when we run 'probe
syscall.*{..} probe syscall.*.return {..}' which will insert more than 500
probes in the kernel.
I think it would be better that we expand it to 512 or more entries.

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           Summary: kprobe_hash_table is too small for systemtap
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: kprobes
        AssignedTo: systemtap at sources dot redhat dot com
        ReportedBy: mhiramat at redhat dot com


http://sourceware.org/bugzilla/show_bug.cgi?id=6989

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[Bug kprobes/6989] kprobe_hash_table is too small for systemtap

[mhiramat at redhat dot com]

------- Additional Comments From mhiramat at redhat dot com  2008-11-05 23:42 -------
Created an attachment (id=3043)
 --> (http://sourceware.org/bugzilla/attachment.cgi?id=3043&action=view)
increase hash_bits to 9 (512 entries)

This patch increases kprobe_hash_bits to 9 from 6.
The average hlist length will be reduced 1/8.


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[Bug kprobes/6989] kprobe_hash_table is too small for systemtap

[ananth at in dot ibm dot com]

------- Additional Comments From ananth at in dot ibm dot com  2008-11-06 03:26 -------
Looks fine to me.

Acked-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>

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[Bug kprobes/6989] kprobe_hash_table is too small for systemtap

[mhiramat at redhat dot com]

------- Additional Comments From mhiramat at redhat dot com  2008-11-08 02:39 -------
Hmm, since kretprobe_table_locks has been __cacheline_aligned, this change
increases the size of kprobes.o so much (about 64KB!).
It was much larger than I thought. We have to fix this problem...

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[Bug kprobes/6989] kprobe_hash_table is too small for systemtap

[mhiramat at redhat dot com]

------- Additional Comments From mhiramat at redhat dot com  2008-11-08 03:35 -------
(In reply to comment #3)
> Hmm, since kretprobe_table_locks has been __cacheline_aligned, this change
> increases the size of kprobes.o so much (about 64KB!).
> It was much larger than I thought. We have to fix this problem...

Hmm, if we separate hash bits of kprobe_table and kretprobe_table,
the object size wasn't increased so much.

   text	   data	    bss	    dec	    hex	filename
   6610	    436	   8840	  15886	   3e0e
/home/mhiramat/kbin/2.6.28-rc3/kernel/kprobes.o
   6621	    436	  10632	  17689	   4519
/home/mhiramat/kbin/2.6.28-rc3/kernel/kprobes.o


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[Bug kprobes/6989] kprobe_hash_table is too small for systemtap

[fche at redhat dot com]

------- Additional Comments From fche at redhat dot com  2010-06-09 13:33 -------
this patch hasn't been merged into upstream linux

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |WONTFIX


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