K. Prasad wrote:
> Hi Ingo,
> Please accept these patches into the rt tree which convert the
> existing RCU tracing mechanism for Preempt RCU and RCU Boost into
> markers.
>
> These patches are based upon the 2.6.24-rc5-rt1 kernel tree.
>
> Along with marker transition, the RCU Tracing infrastructure has also
> been modularised to be built as a kernel module, thereby enabling
> runtime changes to the RCU Tracing infrastructure.
>
> Patch [1/2] - Patch that converts the Preempt RCU tracing in
> rcupreempt.c into markers.
>
> Patch [1/2] - Patch that converts the Preempt RCU Boost tracing in
> rcupreempt-boost.c into markers.
>
I have a technical problem with marker-based RCU tracing: It causes
nasty recursions with latest multi-probe marker patches (sorry, no link
at hand, can be found in latest LTTng, maybe also already in -mm). Those
patches introduce a marker probe trampoline like this:
void marker_probe_cb(const struct marker *mdata, void *call_private,
const char *fmt, ...)
{
va_list args;
char ptype;
/*
* rcu_read_lock does two things : disabling preemption to make sure the
* teardown of the callbacks can be done correctly when they are in
* modules and they insure RCU read coherency.
*/
rcu_read_lock();
preempt_disable();
...
Can we do multi-probe with pure preempt_disable/enable protection? I
guess it's fine with classic RCU, but what about preemptible RCU? Any
suggestion appreciated!
Jan
PS: You will run into this issue if you try to marry latest -rt with
latest LTTng. Straightforward workaround is to comment-out any RCU
trace_mark occurrences.
--
Siemens AG, Corporate Technology, CT SE 2
Corporate Competence Center Embedded Linux
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