Re: Markers: multi-probe locking fun (was: Re: [PATCH 0/2] Markers Implementation for RCU Tracing - Ver II)
* Paul E. McKenney ([EMAIL PROTECTED]) wrote:
> On Tue, Feb 19, 2008 at 03:33:26PM -0500, Mathieu Desnoyers wrote:
> > * Jan Kiszka ([EMAIL PROTECTED]) wrote:
> > > Paul E. McKenney wrote:
> > > > On Mon, Feb 18, 2008 at 01:47:31PM +0100, Jan Kiszka wrote:
> > > >> 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!
> > > >
> > > > If you substitute synchronize_sched() for synchronize_rcu(), this should
> > > > work fine. Of course, this approach would cause RCU tracing to degrade
> > > > latencies somewhat in -rt.
> > > >
> > > > If tracing is using call_rcu(), we will need to add a call_sched()
> > > > or some such.
> > >
> > > You mean something like "#define call_sched call_rcu_classic"?
> > >
> > > I just learned that there is another reason for killing
> > > rcu_read_lock&friends from the marker probes: It can deadlock on -rt
> > > with PREEMPT_RCU_BOOST (hit probe inside rq-lock protected region =>
> > > rcu_read_unlock triggers unboost => stuck on rq_lock :( ).
> > >
> >
> > Yep, ok, let's do this :
> >
> > in include/linux/rcupdate.h
> >
> > #ifndef PREEMPT_RT
> > #define call_sched call_rcu
> > #else
> > #define call_sched call_rcu_classic
> > #endif
> >
> > And I'll adapt the markers accordingly.
>
> Good point, this will indeed work for 2.6.24-rt1!
>
> Will need to do a bit more for 2.6.25-rc1. My current thought is to
> provide a kernel thread that loops over the CPUs, advancing/invoking
> per-CPU lists of callbacks as it does so. Then call_sched() would simply
> enqueue its callback on the current CPU's next list.
>
I just noticed that my multiple probes support patch, that just got into
mainline, does not include the fixes I did you asked for (which includes
protecting with rcu_read_lock). I guess Andrew did not notice the patch.
Therefore, I think we'll need to address this pretty soon to make the
markers play nicely with CONFIG_PREEMPT_RCU.
Mathieu
> Thanx, Paul
--
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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Re: Markers: multi-probe locking fun (was: Re: [PATCH 0/2] Markers Implementation for RCU Tracing - Ver II)
On Tue, Feb 19, 2008 at 05:03:18PM -0500, Mathieu Desnoyers wrote:
> * Paul E. McKenney ([EMAIL PROTECTED]) wrote:
> > On Tue, Feb 19, 2008 at 05:27:40PM +0100, Jan Kiszka wrote:
> > > Paul E. McKenney wrote:
> > > > On Mon, Feb 18, 2008 at 01:47:31PM +0100, Jan Kiszka wrote:
> > > >> 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!
> > > >
> > > > If you substitute synchronize_sched() for synchronize_rcu(), this should
> > > > work fine. Of course, this approach would cause RCU tracing to degrade
> > > > latencies somewhat in -rt.
> > > >
> > > > If tracing is using call_rcu(), we will need to add a call_sched()
> > > > or some such.
> > >
> > > You mean something like "#define call_sched call_rcu_classic"?
> >
> > This would work for Classic RCU. For preemptible RCU, a bit more
> > work is needed.
> >
> > > I just learned that there is another reason for killing
> > > rcu_read_lock&friends from the marker probes: It can deadlock on -rt
> > > with PREEMPT_RCU_BOOST (hit probe inside rq-lock protected region =>
> > > rcu_read_unlock triggers unboost => stuck on rq_lock :( ).
> >
> > OK, good to know. Guess we need a call_sched() for -rt and for
> > preemptible RCU sooner rather than later...
> >
>
> Yup, I would need call_sched() and sched_barrier().
Ah, good point, kprobes does indeed use modules!
Thanx, Paul
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Re: Markers: multi-probe locking fun (was: Re: [PATCH 0/2] Markers Implementation for RCU Tracing - Ver II)
On Tue, Feb 19, 2008 at 03:33:26PM -0500, Mathieu Desnoyers wrote:
> * Jan Kiszka ([EMAIL PROTECTED]) wrote:
> > Paul E. McKenney wrote:
> > > On Mon, Feb 18, 2008 at 01:47:31PM +0100, Jan Kiszka wrote:
> > >> 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!
> > >
> > > If you substitute synchronize_sched() for synchronize_rcu(), this should
> > > work fine. Of course, this approach would cause RCU tracing to degrade
> > > latencies somewhat in -rt.
> > >
> > > If tracing is using call_rcu(), we will need to add a call_sched()
> > > or some such.
> >
> > You mean something like "#define call_sched call_rcu_classic"?
> >
> > I just learned that there is another reason for killing
> > rcu_read_lock&friends from the marker probes: It can deadlock on -rt
> > with PREEMPT_RCU_BOOST (hit probe inside rq-lock protected region =>
> > rcu_read_unlock triggers unboost => stuck on rq_lock :( ).
> >
>
> Yep, ok, let's do this :
>
> in include/linux/rcupdate.h
>
> #ifndef PREEMPT_RT
> #define call_sched call_rcu
> #else
> #define call_sched call_rcu_classic
> #endif
>
> And I'll adapt the markers accordingly.
Good point, this will indeed work for 2.6.24-rt1!
Will need to do a bit more for 2.6.25-rc1. My current thought is to
provide a kernel thread that loops over the CPUs, advancing/invoking
per-CPU lists of callbacks as it does so. Then call_sched() would simply
enqueue its callback on the current CPU's next list.
Thanx, Paul
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Re: Markers: multi-probe locking fun (was: Re: [PATCH 0/2] Markers Implementation for RCU Tracing - Ver II)
* Paul E. McKenney ([EMAIL PROTECTED]) wrote:
> On Tue, Feb 19, 2008 at 05:27:40PM +0100, Jan Kiszka wrote:
> > Paul E. McKenney wrote:
> > > On Mon, Feb 18, 2008 at 01:47:31PM +0100, Jan Kiszka wrote:
> > >> 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!
> > >
> > > If you substitute synchronize_sched() for synchronize_rcu(), this should
> > > work fine. Of course, this approach would cause RCU tracing to degrade
> > > latencies somewhat in -rt.
> > >
> > > If tracing is using call_rcu(), we will need to add a call_sched()
> > > or some such.
> >
> > You mean something like "#define call_sched call_rcu_classic"?
>
> This would work for Classic RCU. For preemptible RCU, a bit more
> work is needed.
>
> > I just learned that there is another reason for killing
> > rcu_read_lock&friends from the marker probes: It can deadlock on -rt
> > with PREEMPT_RCU_BOOST (hit probe inside rq-lock protected region =>
> > rcu_read_unlock triggers unboost => stuck on rq_lock :( ).
>
> OK, good to know. Guess we need a call_sched() for -rt and for
> preemptible RCU sooner rather than later...
>
Yup, I would need call_sched() and sched_barrier().
Thanks,
Mathieu
> Thanx, Paul
--
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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Re: Markers: multi-probe locking fun (was: Re: [PATCH 0/2] Markers Implementation for RCU Tracing - Ver II)
On Tue, Feb 19, 2008 at 05:27:40PM +0100, Jan Kiszka wrote:
> Paul E. McKenney wrote:
> > On Mon, Feb 18, 2008 at 01:47:31PM +0100, Jan Kiszka wrote:
> >> 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!
> >
> > If you substitute synchronize_sched() for synchronize_rcu(), this should
> > work fine. Of course, this approach would cause RCU tracing to degrade
> > latencies somewhat in -rt.
> >
> > If tracing is using call_rcu(), we will need to add a call_sched()
> > or some such.
>
> You mean something like "#define call_sched call_rcu_classic"?
This would work for Classic RCU. For preemptible RCU, a bit more
work is needed.
> I just learned that there is another reason for killing
> rcu_read_lock&friends from the marker probes: It can deadlock on -rt
> with PREEMPT_RCU_BOOST (hit probe inside rq-lock protected region =>
> rcu_read_unlock triggers unboost => stuck on rq_lock :( ).
OK, good to know. Guess we need a call_sched() for -rt and for
preemptible RCU sooner rather than later...
Thanx, Paul
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Re: Markers: multi-probe locking fun (was: Re: [PATCH 0/2] Markers Implementation for RCU Tracing - Ver II)
* Jan Kiszka ([EMAIL PROTECTED]) wrote:
> Paul E. McKenney wrote:
> > On Mon, Feb 18, 2008 at 01:47:31PM +0100, Jan Kiszka wrote:
> >> 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!
> >
> > If you substitute synchronize_sched() for synchronize_rcu(), this should
> > work fine. Of course, this approach would cause RCU tracing to degrade
> > latencies somewhat in -rt.
> >
> > If tracing is using call_rcu(), we will need to add a call_sched()
> > or some such.
>
> You mean something like "#define call_sched call_rcu_classic"?
>
> I just learned that there is another reason for killing
> rcu_read_lock&friends from the marker probes: It can deadlock on -rt
> with PREEMPT_RCU_BOOST (hit probe inside rq-lock protected region =>
> rcu_read_unlock triggers unboost => stuck on rq_lock :( ).
>
Yep, ok, let's do this :
in include/linux/rcupdate.h
#ifndef PREEMPT_RT
#define call_sched call_rcu
#else
#define call_sched call_rcu_classic
#endif
And I'll adapt the markers accordingly.
Mathieu
> Jan
>
> --
> Siemens AG, Corporate Technology, CT SE 2
> Corporate Competence Center Embedded Linux
--
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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Markers: multi-probe locking fun (was: Re: [PATCH 0/2] Markers Implementation for RCU Tracing - Ver II)
Paul E. McKenney wrote:
> On Mon, Feb 18, 2008 at 01:47:31PM +0100, Jan Kiszka wrote:
>> 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!
>
> If you substitute synchronize_sched() for synchronize_rcu(), this should
> work fine. Of course, this approach would cause RCU tracing to degrade
> latencies somewhat in -rt.
>
> If tracing is using call_rcu(), we will need to add a call_sched()
> or some such.
You mean something like "#define call_sched call_rcu_classic"?
I just learned that there is another reason for killing
rcu_read_lock&friends from the marker probes: It can deadlock on -rt
with PREEMPT_RCU_BOOST (hit probe inside rq-lock protected region =>
rcu_read_unlock triggers unboost => stuck on rq_lock :( ).
Jan
--
Siemens AG, Corporate Technology, CT SE 2
Corporate Competence Center Embedded Linux
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Re: [PATCH 0/2] Markers Implementation for RCU Tracing - Ver II
* Paul E. McKenney ([EMAIL PROTECTED]) wrote:
> On Mon, Feb 18, 2008 at 01:47:31PM +0100, Jan Kiszka wrote:
> > 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!
>
> If you substitute synchronize_sched() for synchronize_rcu(), this should
> work fine. Of course, this approach would cause RCU tracing to degrade
> latencies somewhat in -rt.
>
> If tracing is using call_rcu(), we will need to add a call_sched()
> or some such.
>
Yes, I use call_rcu, so I guess a call_sched would be useful here.
Mathieu
> Thanx, Paul
>
> > 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
--
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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Re: [PATCH 0/2] Markers Implementation for RCU Tracing - Ver II
On Mon, Feb 18, 2008 at 01:47:31PM +0100, Jan Kiszka wrote:
> 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!
If you substitute synchronize_sched() for synchronize_rcu(), this should
work fine. Of course, this approach would cause RCU tracing to degrade
latencies somewhat in -rt.
If tracing is using call_rcu(), we will need to add a call_sched()
or some such.
Thanx, Paul
> 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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Re: [PATCH 0/2] Markers Implementation for RCU Tracing - Ver II
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.
>
> Thanks,
> K.Prasad
> ([EMAIL PROTECTED])
The correct marker annotation for "no arguments" is MARK_NOARGS.
Signed-off-by: Jan Kiszka <[EMAIL PROTECTED]>
---
kernel/rcupreempt-boost.c | 24
kernel/rcupreempt.c | 42 +-
2 files changed, 33 insertions(+), 33 deletions(-)
Index: b/kernel/rcupreempt-boost.c
===
--- a/kernel/rcupreempt-boost.c
+++ b/kernel/rcupreempt-boost.c
@@ -57,10 +57,10 @@ static void rcu_boost_task(struct task_s
WARN_ON(!irqs_disabled());
WARN_ON_SMP(!spin_is_locked(&task->pi_lock));
- trace_mark(task_boost_called, "NULL");
+ trace_mark(task_boost_called, MARK_NOARGS);
if (task->rcu_prio < task->prio) {
- trace_mark(task_boosted, "NULL");
+ trace_mark(task_boosted, MARK_NOARGS);
task_setprio(task, task->rcu_prio);
}
}
@@ -84,7 +84,7 @@ void __rcu_preempt_boost(void)
WARN_ON(!current->rcu_read_lock_nesting);
- trace_mark(boost_called, "NULL");
+ trace_mark(boost_called, MARK_NOARGS);
/* check to see if we are already boosted */
if (unlikely(rcu_is_boosted(curr)))
@@ -102,7 +102,7 @@ void __rcu_preempt_boost(void)
curr->rcub_rbdp = rbd;
- trace_mark(try_boost, "NULL");
+ trace_mark(try_boost, MARK_NOARGS);
prio = rt_mutex_getprio(curr);
@@ -111,7 +111,7 @@ void __rcu_preempt_boost(void)
if (prio <= rbd->rbs_prio)
goto out;
- trace_mark(boosted, "NULL");
+ trace_mark(boosted, MARK_NOARGS);
curr->rcu_prio = rbd->rbs_prio;
rcu_boost_task(curr);
@@ -136,7 +136,7 @@ void __rcu_preempt_unboost(void)
int prio;
unsigned long flags;
- trace_mark(unboost_called, "NULL");
+ trace_mark(unboost_called, MARK_NOARGS);
/* if not boosted, then ignore */
if (likely(!rcu_is_boosted(curr)))
@@ -174,7 +174,7 @@ void __rcu_preempt_unboost(void)
list_del_init(&curr->rcub_entry);
- trace_mark(unboosted, "NULL");
+ trace_mark(unboosted, MARK_NOARGS);
curr->rcu_prio = MAX_PRIO;
@@ -235,7 +235,7 @@ static int __rcu_boost_readers(struct rc
* Another task may have taken over.
*/
if (curr->rcu_preempt_counter != rcu_boost_counter) {
- trace_mark(over_taken, "NULL");
+ trace_mark(over_taken, MARK_NOARGS);
return 1;
}
@@ -266,7 +266,7 @@ void rcu_boost_readers(void)
prio = rt_mutex_getprio(curr);
- trace_mark(try_boost_readers, "NULL");
+ trace_mark(try_boost_readers, MARK_NOARGS);
if (prio >= rcu_boost_prio) {
/* already boosted */
@@ -276,7 +276,7 @@ void rcu_boost_readers(void)
rcu_boost_prio = prio;
- trace_mark(boost_readers, "NULL");
+ trace_mark(boost_readers, MARK_NOARGS);
/* Flag that we are the one to unboost */
curr->rcu_preempt_counter = ++rcu_boost_counter;
@@ -309,12 +309,12 @@ void rcu_unboost_readers(void)
spin_lock_irqsave(&rcu_boost_wake_lock, flags);
- trace_mark(try_unboost_readers, "NULL");
+ trace_mark(try_unboost_readers, MARK_NOARGS);
if (current->rcu_preempt_counter != rcu_boost_counter)
goto out;
- trace_mark(unboost_readers, "NULL");
+ trace_mark(unboost_readers, MARK_NOARGS);
/*
* We could also put in something that
Index: b/kernel/rcupreempt.c
===
--- a/kernel/rcupreempt.c
+++ b/kernel/rcupreempt.c
@@ -308,7 +308,7 @@ static void __rcu_advance_callbacks(stru
if (rdp->waitlist[GP_STAGES - 1] != NULL) {
*rdp->donetail = rdp->waitlist[GP_STAGES - 1];
rdp->donetail = rdp->waittail[GP_STAGES - 1];
- trace_mark(rcupreempt_trace_move2done, "NULL");
+ trace_mark(rcupreempt_trace_move2done, MARK_NOARGS);
}
for (i = GP_STAGES - 2; i >= 0; i--) {
if (rdp->waitlist[i] != NULL) {
@@ -327,7 +327
Re: [PATCH 0/2] Markers Implementation for RCU Tracing - Ver II
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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