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78 lines
3.4 KiB
Plaintext
78 lines
3.4 KiB
Plaintext
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**************************************************************************
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* The following are notes for any script that uses the "fbt" provider.
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* To identify these scripts, check the "STABILITY" section of the script's
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* man page, or try grepping for "fbt" on the script.
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*
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* $Id: ALLfbt_notes.txt 44 2007-09-17 07:47:20Z brendan $
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*
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* COPYRIGHT: Copyright (c) 2007 Brendan Gregg.
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**************************************************************************
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What is the "fbt" provider?...
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* A DTrace library of probes that instruments raw kernel function calls.
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* An "unstable" provider; meaning, scripts written using "fbt" are not
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guarenteed to work on future versions of the OS - including after
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patching the kernel.
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In a perfect world...
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* None of the DTraceToolkit scripts would use the "fbt" provider; instead
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they would all use stable providers such as "proc", "sched", "io", etc.
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* All the DTraceToolkit scripts would run on any system that supports DTrace.
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In the real world...
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* Not all stable providers exist yet. Many are in development, such as
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stable networking providers.
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* In the meantime, useful tools such as "tcpsnoop" and "tcptop" can
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only be written using the unstable "fbt" provider (and these scripts have
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broken several times due to kernel changes since they were first written).
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* "fbt" provider based scripts,
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- only run on a particular OS (eg, Solaris)
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- may only run on a particular version of an OS (eg, Solaris 10 3/05)
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- are likely to break for future OS releases (eg, Solaris 10 6/06)
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* "fbt" provider based scripts also make the impossible possible, albiet
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in a very unstable way, as a temporary solution while stable providers
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are still in development.
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* Once stable providers exist, "fbt" scripts can be rewritten to use them;
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however these new scripts will only run on newer OS builds that support
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the stable providers. (in other words, this won't help you if you remain
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on Solaris 10 6/06; you'll need to upgrade, or survive with "fbt").
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* Only some of the DTraceToolkit scripts use "fbt", and only a portion of
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those have encountered stability issues - so this issue is limited.
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The "fbt" provider exports raw kernel implementation, which isn't guarenteed
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to be stable nor should it ever be (to do so would freeze kernel development
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and bug fixes). The only practical solution is the development and
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integration of stable providers (although that doesn't help people who keep
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running older versions of the OS).
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More harm than good?...
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Is the inclusion of these "fbt" scripts more harm than good? Consider,
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* the good,
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- shows what is possible with DTrace
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- should help a number of people solve specific performance issues,
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on systems where they run
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- a customer who really wants these scripts but on an OS version
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where they don't work, have at least the source as a starting
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point (and in some cases, the fix was trivial)
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* the bad,
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- teases and frustrates people who find these scripts don't work
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on their OS
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To minimise this issue, only a small number of "fbt" scripts have been
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included, and they have been documented (see their man page) as unstable.
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Can I help?...
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If you really like an "fbt" based script and would like to keep using it
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in a stable way, it may help to raise that with your vendor (Sun for Solaris,
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Apple for MacOS). Sun has OpenSolaris forums, such as dtrace-discuss, which
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are read by their engineers and the public.
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