Re: [Ltt-dev] LTTng 0.10.0-pre23 (fix)

[David Smith <dsmith at redhat dot com>]

Mike Mason wrote:
> Mathieu Desnoyers wrote:
>> * Mathieu Desnoyers (compudj@krystal.dyndns.org) wrote:
>>> * Mathieu Desnoyers (compudj@krystal.dyndns.org) wrote:
>>>> Hi,
>>>>
>>>> I just released lttng 0.10.0-pre22 for Linux 2.6.24-rc2, which adds
>>>> support for multiple callbacks connected to a single marker. I make
>>>> extensive use the kernel RCU mechanism so batch connexion of probes to
>>>> different markers can be done as quickly as possible, requiring to wait
>>>> for quiescent state only when necessary. It proves to be important when
>>>> connecting probes on busy systems, where waiting for ~50
>>>> synchronize_sched() could take about 1-2 minutes.
>>>>
>>> Actually this release is pre21, not pre22.
>>>
>>
>> LTTng 0.10.0-pre23 fixes a bug in an inaccurate assumption that a
>> function pointer is always aligned on (at least) 2 bytes boundaries.
>> It's not on some architectures.
> 
> I tested your changes on x86_64 using multiple instances of the
> probe-example code.  Everything seems to work fine.  The code itself
> looks fine, too, though I'm no RCU expert.  The SystemTap support for
> markers will have to change again since the register and unregister
> interfaces have changed.  I also noticed the arm and disarm functions
> are gone.

Systemtap has been updated to work with latest LTTNG patch
patch-2.6.24-rc2-lttng-0.10-pre23.tar.bz2, with one exception.

Mathieu, in samples/markers/probe_example.c, you've got:

===
void
probe_subsystem_eventb(void *probe_data, void *call_data,
	const char *format, va_list *args) __attribute__((aligned(2)));
===

However, when I try to compile that (on fedora 7) I get:

===
probe-example.c:25: error: alignment may not be specified for
‘probe_subsystem_eventb’
===

Of course removing the '__attribute__((aligned(2)))' makes it work
correctly.  Am I missing something here?

-- 
David Smith
dsmith@redhat.com
Red Hat
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