* [Bug runtime/11592] New: sdt.h should have a 'disable-semaphores' override option
@ 2010-05-12 17:16 fche at redhat dot com
2010-05-12 17:43 ` [Bug runtime/11592] " alexl at redhat dot com
` (6 more replies)
0 siblings, 7 replies; 8+ messages in thread
From: fche at redhat dot com @ 2010-05-12 17:16 UTC (permalink / raw)
To: systemtap
See https://bugzilla.gnome.org/show_bug.cgi?id=606044
for a situation where semaphores constitute a performance
regression. (In this case, argument setup is small compared
to the semaphore value check.)
Unless we can automate per-marker semaphore presence, we should
provide an override capability. It may need to be nothing larger
than allowing an application .c file to define
#define STAP_NO_SEMAPHORES
which then the dtrace.in-generated script would observe and avoid
defining STAP_HAS_SEMAPHORES.
--
Summary: sdt.h should have a 'disable-semaphores' override option
Product: systemtap
Version: unspecified
Status: NEW
Severity: normal
Priority: P2
Component: runtime
AssignedTo: systemtap at sources dot redhat dot com
ReportedBy: fche at redhat dot com
CC: scox at redhat dot com
http://sourceware.org/bugzilla/show_bug.cgi?id=11592
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* [Bug runtime/11592] sdt.h should have a 'disable-semaphores' override option
2010-05-12 17:16 [Bug runtime/11592] New: sdt.h should have a 'disable-semaphores' override option fche at redhat dot com
@ 2010-05-12 17:43 ` alexl at redhat dot com
2010-05-12 17:48 ` fche at redhat dot com
` (5 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: alexl at redhat dot com @ 2010-05-12 17:43 UTC (permalink / raw)
To: systemtap
------- Additional Comments From alexl at redhat dot com 2010-05-12 15:20 -------
Why doesn't semaphores work like the is-enabled stuff in dtrace:
http://blogs.sun.com/ahl/entry/user_land_tracing_gets_better
Seems like that would be much more useful than automatically enabling it for all
probes. And its dtrace compatible to boot.
--
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CC| |alexl at redhat dot com
http://sourceware.org/bugzilla/show_bug.cgi?id=11592
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* [Bug runtime/11592] sdt.h should have a 'disable-semaphores' override option
2010-05-12 17:16 [Bug runtime/11592] New: sdt.h should have a 'disable-semaphores' override option fche at redhat dot com
2010-05-12 17:43 ` [Bug runtime/11592] " alexl at redhat dot com
@ 2010-05-12 17:48 ` fche at redhat dot com
2010-05-14 19:44 ` alexl at redhat dot com
` (4 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: fche at redhat dot com @ 2010-05-12 17:48 UTC (permalink / raw)
To: systemtap
------- Additional Comments From fche at redhat dot com 2010-05-12 15:24 -------
(In reply to comment #1)
> Why doesn't semaphores work like the is-enabled stuff in dtrace:
Right, that foo_IS_ENABLED() is already supported as is.
> Seems like that would be much more useful than automatically enabling it for all
> probes.
The argument has been that we've encountered cases where sdt.h macros
were called with fairly heavy-weight arguments, but without an
explicit foo_IS_ENABLED() wrapper. In these cases, it helped. But now
there is evidence that it also hurts sometimes, so we need to re-evaluate.
--
http://sourceware.org/bugzilla/show_bug.cgi?id=11592
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* [Bug runtime/11592] sdt.h should have a 'disable-semaphores' override option
2010-05-12 17:16 [Bug runtime/11592] New: sdt.h should have a 'disable-semaphores' override option fche at redhat dot com
2010-05-12 17:43 ` [Bug runtime/11592] " alexl at redhat dot com
2010-05-12 17:48 ` fche at redhat dot com
@ 2010-05-14 19:44 ` alexl at redhat dot com
2010-05-25 15:11 ` walters at verbum dot org
` (3 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: alexl at redhat dot com @ 2010-05-14 19:44 UTC (permalink / raw)
To: systemtap
------- Additional Comments From alexl at redhat dot com 2010-05-14 07:20 -------
I don't particularly care if semaphores are automatically enabled for probes or
not, as long as there is a way to enable/disable it. For glib i want to disable
it and do it manually where needed. This should imho be the right approach for
all probe sets, but I realize not everyone need to be as careful about
performance issues as core glib functionallity.
--
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* [Bug runtime/11592] sdt.h should have a 'disable-semaphores' override option
2010-05-12 17:16 [Bug runtime/11592] New: sdt.h should have a 'disable-semaphores' override option fche at redhat dot com
` (2 preceding siblings ...)
2010-05-14 19:44 ` alexl at redhat dot com
@ 2010-05-25 15:11 ` walters at verbum dot org
2010-05-25 15:20 ` fche at redhat dot com
` (2 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: walters at verbum dot org @ 2010-05-25 15:11 UTC (permalink / raw)
To: systemtap
------- Additional Comments From walters at verbum dot org 2010-05-25 13:30 -------
Created an attachment (id=4811)
--> (http://sourceware.org/bugzilla/attachment.cgi?id=4811&action=view)
0001-dtrace.in-Allow-definition-of-STAP_LIGHTWEIGHT_PROBE.patch
Something like this (untested) patch?
--
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* [Bug runtime/11592] sdt.h should have a 'disable-semaphores' override option
2010-05-12 17:16 [Bug runtime/11592] New: sdt.h should have a 'disable-semaphores' override option fche at redhat dot com
` (3 preceding siblings ...)
2010-05-25 15:11 ` walters at verbum dot org
@ 2010-05-25 15:20 ` fche at redhat dot com
2010-05-26 1:31 ` alexl at redhat dot com
2010-05-27 14:19 ` scox at redhat dot com
6 siblings, 0 replies; 8+ messages in thread
From: fche at redhat dot com @ 2010-05-25 15:20 UTC (permalink / raw)
To: systemtap
------- Additional Comments From fche at redhat dot com 2010-05-25 13:35 -------
Or maybe we should flip the default over to no-semaphores, and have
a user specifically request it:
-D STAP_SDT_IMPLICIT_SEMAPHORES
(since they can already use foo_ENABLED() for explicit conditions).
--
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* [Bug runtime/11592] sdt.h should have a 'disable-semaphores' override option
2010-05-12 17:16 [Bug runtime/11592] New: sdt.h should have a 'disable-semaphores' override option fche at redhat dot com
` (4 preceding siblings ...)
2010-05-25 15:20 ` fche at redhat dot com
@ 2010-05-26 1:31 ` alexl at redhat dot com
2010-05-27 14:19 ` scox at redhat dot com
6 siblings, 0 replies; 8+ messages in thread
From: alexl at redhat dot com @ 2010-05-26 1:31 UTC (permalink / raw)
To: systemtap
------- Additional Comments From alexl at redhat dot com 2010-05-25 15:11 -------
I agree with frank. Additionally, thats what dtrace does.
--
http://sourceware.org/bugzilla/show_bug.cgi?id=11592
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* [Bug runtime/11592] sdt.h should have a 'disable-semaphores' override option
2010-05-12 17:16 [Bug runtime/11592] New: sdt.h should have a 'disable-semaphores' override option fche at redhat dot com
` (5 preceding siblings ...)
2010-05-26 1:31 ` alexl at redhat dot com
@ 2010-05-27 14:19 ` scox at redhat dot com
6 siblings, 0 replies; 8+ messages in thread
From: scox at redhat dot com @ 2010-05-27 14:19 UTC (permalink / raw)
To: systemtap
--
What |Removed |Added
----------------------------------------------------------------------------
AssignedTo|systemtap at sources dot |scox at redhat dot com
|redhat dot com |
Status|NEW |ASSIGNED
http://sourceware.org/bugzilla/show_bug.cgi?id=11592
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2010-05-12 17:16 [Bug runtime/11592] New: sdt.h should have a 'disable-semaphores' override option fche at redhat dot com
2010-05-12 17:43 ` [Bug runtime/11592] " alexl at redhat dot com
2010-05-12 17:48 ` fche at redhat dot com
2010-05-14 19:44 ` alexl at redhat dot com
2010-05-25 15:11 ` walters at verbum dot org
2010-05-25 15:20 ` fche at redhat dot com
2010-05-26 1:31 ` alexl at redhat dot com
2010-05-27 14:19 ` scox at redhat dot com
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