Bug 6432 - use 2.6.26 probe_kernel_{read,write}

Bug#:	6432 alias:	Hardware:	Reporter:	Frank Ch. Eigler <fche@redhat.com>
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Status:	RESOLVED	Priority:
Resolution:	FIXED	Severity:
Assigned To:	Unassigned <systemtap@sources.redhat.com>	Target Milestone:

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Attachment	Description	Type	Created	Actions
stap-probe-kernel.patch	Use probe_kernel functions in deref macros	patch	2008-05-27 19:25	Edit \| Diff
deref-long.stp	Test the overhead of dereferencing numbers	text/plain	2008-05-27 19:30	Edit None
deref-string.stp	Test the overhead of dereferencing strings	text/plain	2008-05-27 19:32	Edit None
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Bug 6432 depends on:			Show dependency tree Show dependency graph
Bug 6432 blocks:			Show dependency tree Show dependency graph

Additional Comments:

Leave as RESOLVED FIXED
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Description:

Last confirmed: 0000-00-00 00:00

Opened: 2008-04-19 16:51

*** Bug 6433 has been marked as a duplicate of this bug. ***

------- Additional Comment #1 From Frank Ch. Eigler 2008-04-21 15:43 -------

*** Bug 6434 has been marked as a duplicate of this bug. ***

------- Additional Comment #2 From Frank Ch. Eigler 2008-04-21 15:44 -------

*** Bug 6435 has been marked as a duplicate of this bug. ***

------- Additional Comment #3 From Josh Stone 2008-05-27 19:25 -------

Created an attachment (id=2757)
Use probe_kernel functions in deref macros

This changes the deref macros to use probe_kernel, but there's a performance
hit, probably due to no longer inlining the dereferencing activity.  Simple
benchmark scripts to follow...

------- Additional Comment #4 From Josh Stone 2008-05-27 19:30 -------

Created an attachment (id=2758)
Test the overhead of dereferencing numbers

Run as 'stap -gt deref-long.stp', and add '-DTEST_DIRECT' for direct memory
access.  My results on 2.6.26-rc3 x86_64:

OLD: 
direct: 1057min/1268avg/10905max
deref: 1073min/1305avg/9405max

NEW:
direct: 1050min/1235avg/9443max
deref: 1238min/1473avg/8850max

------- Additional Comment #5 From Josh Stone 2008-05-27 19:32 -------

Created an attachment (id=2759)
Test the overhead of dereferencing strings

Run as 'stap -gt deref-string.stp', and add '-DTEST_DIRECT' for direct memory
access.  My results on 2.6.26-rc3 x86_64:

OLD:
direct: 1725min/2072avg/10283max
deref: 1778min/2085avg/10950max

NEW:
direct: 1650min/2012avg/10613max
deref: 2152min/2476avg/12563max

------- Additional Comment #6 From Josh Stone 2008-05-27 19:40 -------

So given the performance disadvantage, is this still a change you want to 
make?  Or can anyone see a way to improve the efficiency?

------- Additional Comment #7 From Frank Ch. Eigler 2008-05-27 20:21 -------

Josh, thanks for trying this out.  Please commit the patch,
but #if-0'd out, so that some day we can easily try again,
and resolve/wontfix this bug.

------- Additional Comment #8 From Josh Stone 2008-05-27 23:33 -------

Committed in 2cda5f46cba978e19590efd7fee0b3075f8eb8df with the autoconf test
disabled.  One can use -DSTAPCONF_PROBE_KERNEL to enable it manually.