* [Bug runtime/20286] New: probe handlers using hrtimers taking too long
@ 2016-06-21 20:39 dsmith at redhat dot com
2016-06-21 21:18 ` [Bug documentation/20286] " dsmith at redhat dot com
2016-06-21 21:39 ` dsmith at redhat dot com
0 siblings, 2 replies; 3+ messages in thread
From: dsmith at redhat dot com @ 2016-06-21 20:39 UTC (permalink / raw)
To: systemtap
https://sourceware.org/bugzilla/show_bug.cgi?id=20286
Bug ID: 20286
Summary: probe handlers using hrtimers taking too long
Product: systemtap
Version: unspecified
Status: NEW
Severity: normal
Priority: P2
Component: runtime
Assignee: systemtap at sourceware dot org
Reporter: dsmith at redhat dot com
Target Milestone: ---
When running the full testsuite (in parallel mode, but I'm not sure it
matters), I see the following on the console (3.10.0-442.el7.ppc64):
[ 6881.740026] hrtimer: interrupt took 3721 ns
While that doesn't look too alarming, what it means is that the next timer has
already expired because the current timer callback took too long. I'm looking
at the source of hrtimer_interrupt() in kernel/time/hrtimer.c. Here's a comment
from there:
* The next timer was already expired due to:
* - tracing
* - long lasting callbacks
* - being scheduled away when running in a VM
*
* We need to prevent that we loop forever in the hrtimer
* interrupt routine. We give it 3 attempts to avoid
* overreacting on some spurious event.
We may need to lower MAXACTION for probes that use hrtimers or think of some
other way to not take too long in an hrtimer-based probe. This probably should
depend on the timer's frequency (i.e. the faster the timer, the less actions
should be allowed).
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* [Bug documentation/20286] probe handlers using hrtimers taking too long
2016-06-21 20:39 [Bug runtime/20286] New: probe handlers using hrtimers taking too long dsmith at redhat dot com
@ 2016-06-21 21:18 ` dsmith at redhat dot com
2016-06-21 21:39 ` dsmith at redhat dot com
1 sibling, 0 replies; 3+ messages in thread
From: dsmith at redhat dot com @ 2016-06-21 21:18 UTC (permalink / raw)
To: systemtap
https://sourceware.org/bugzilla/show_bug.cgi?id=20286
David Smith <dsmith at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Component|runtime |documentation
--- Comment #1 from David Smith <dsmith at redhat dot com> ---
After a conversation with Frank Eigler, we're not sure there is much we can do
here. The probes are runing long because someone needed them to run long. If we
limit the runtime, then that just means that we block some types of probes
entirely. So, we'll continue to let them run, and perhaps skipping some.
I'll try to document this.
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* [Bug documentation/20286] probe handlers using hrtimers taking too long
2016-06-21 20:39 [Bug runtime/20286] New: probe handlers using hrtimers taking too long dsmith at redhat dot com
2016-06-21 21:18 ` [Bug documentation/20286] " dsmith at redhat dot com
@ 2016-06-21 21:39 ` dsmith at redhat dot com
1 sibling, 0 replies; 3+ messages in thread
From: dsmith at redhat dot com @ 2016-06-21 21:39 UTC (permalink / raw)
To: systemtap
https://sourceware.org/bugzilla/show_bug.cgi?id=20286
David Smith <dsmith at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution|--- |FIXED
--- Comment #2 from David Smith <dsmith at redhat dot com> ---
Note added to stapprobes man page in commit 42b9738.
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