[Bug translator/10995] New: on-the-fly enabled/disabled probes

[Bug translator/10995] New: on-the-fly enabled/disabled probes

[fche at redhat dot com]

Bug #4935 included script syntax to designate probe enabling conditions,
and bug #6933 has implemented some support for lightweight kprobe
dis/rearming, but the translator is not actually emitting any code to
connect the two.

We should extend the translator and the various probe point family
implementations (tapset*cxx) to support disarm/rearm operations.
The translator would then have to emit code for the probe point
conditionals to invoke disarm/rearm based upon transitions of the
predicate expression values.

-- 
           Summary: on-the-fly enabled/disabled probes
           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
 BugsThisDependsOn: 4935,6933


http://sourceware.org/bugzilla/show_bug.cgi?id=10995

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[Bug translator/10995] on-the-fly enabled/disabled probes

[jkenisto at us dot ibm dot com]

------- Additional Comments From jkenisto at us dot ibm dot com  2009-11-21 01:04 -------
On a related note, in the SystemTap-resident versions of uprobes, a u[ret]probe
handler can call [un]register_u[ret]probe().  A handler can even unregister
itself.  See Section 4.4, "User's Callback for Delayed Registrations", in
runtime/uprobes/uprobes.txt.

U[ret]probe handlers can block, so they could also [un]register k[ret]probes.

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http://sourceware.org/bugzilla/show_bug.cgi?id=10995

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[Bug translator/10995] on-the-fly enabled/disabled probes

[fche at redhat dot com]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
OtherBugsDependingO|                            |11179
              nThis|                            |


http://sourceware.org/bugzilla/show_bug.cgi?id=10995

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[Bug translator/10995] on-the-fly enabled/disabled probes

[fche at redhat dot com]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
OtherBugsDependingO|                            |11550
              nThis|                            |


http://sourceware.org/bugzilla/show_bug.cgi?id=10995

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[Bug translator/10995] on-the-fly enabled/disabled probes

[fche at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=10995

--- Comment #2 from Frank Ch. Eigler <fche at redhat dot com> 2012-12-11 20:23:14 UTC ---
bug #6503 added a derived_probe_group code generation function to
emit_module_refresh().  The code this generates would need to be extended with
per-probe predicate/registration-status bits in the runtime, and with code to
do any sort of lightweight arming/disarming that the probe system permits.  The
predicate-status bits would be mutexfully maintained by other code that
re-evaluates the probe predicate expressions periodically, or whenever the
input globals are suspected to change value.

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[Bug translator/10995] on-the-fly enabled/disabled probes

[jlebon at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=10995

Jonathan Lebon <jlebon at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jlebon at redhat dot com

--- Comment #3 from Jonathan Lebon <jlebon at redhat dot com> ---
I've been working on this feature for a while. I've just pushed to the
jlebon/onthefly branch preliminary work to support this. Currently supported
are hrtimer probes and kprobes.

You can use the -DDEBUG_STP_ON_THE_FLY directive to see it in action during
runtime (outputs to dmesg). Here's a sample (with relevant dmesg output
interspersed):

$ stap -DDEBUG_STP_ON_THE_FLY -e '
global enabled = 0
probe timer.s(1) if (enabled) {
   println("enabled!")
}
probe timer.s(5) {
   println("toggling enable")
   enabled = !enabled
}'



***** DMESG *****
[ 1490.643619] stap_9ea625b9fc91177d0b2a6490acd27b5_20639: systemtap:
2.6/0.158, base: ffffffffa0295000, memory: 31data/24text/1ctx/2058net/17alloc
kb, probes: 2
[ 1490.643625] systemtap_module_init:470 not starting (hrtimer) pidx 0
[ 1490.644421] systemtap_module_init:486 started (hrtimer) pidx 1
*****************



toggling enable



***** DMESG *****
[ 1495.644483] _stp_hrtimer_notify_function:298 scheduling work
[ 1495.645261] module_refresher:68 calling systemtap_module_refresh()
[ 1495.645474] systemtap_module_refresh:538 enabling (hrtimer) pidx 0
*****************



enabled!
enabled!
enabled!
enabled!
toggling enable



***** DMESG *****
[ 1500.644483] _stp_hrtimer_notify_function:298 scheduling work
[ 1500.645275] module_refresher:68 calling systemtap_module_refresh()
[ 1500.646036] systemtap_module_refresh:541 disabling (hrtimer) pidx 0
*****************



toggling enable



***** DMESG *****
[ 1505.644484] _stp_hrtimer_notify_function:298 scheduling work
[ 1505.645287] module_refresher:68 calling systemtap_module_refresh()
[ 1505.646069] systemtap_module_refresh:538 enabling (hrtimer) pidx 0
*****************

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[Bug translator/10995] on-the-fly enabled/disabled probes

[jlebon at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=10995

Jonathan Lebon <jlebon at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|systemtap at sourceware dot org    |jlebon at redhat dot com

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