tracing: Let tracepoints have data passed to tracepoint callbacks
in [Kernel]
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From: Li Zefan on 27 Apr 2010 05:10 Steven Rostedt wrote: > From: Steven Rostedt <srostedt(a)redhat.com> > > This patch allows data to be passed to the tracepoint callbacks > if the tracepoint was created to do so. > > If a tracepoint is defined with: > > DECLARE_TRACE_DATA(name, proto, args) > > Then a registered function can also register data to be passed > to the tracepoint as such: > > DECLARE_TRACE_DATA(mytracepoint, TP_PROTO(int status), TP_ARGS(status)); > > /* In the C file */ > > DEFINE_TRACE(mytracepoint, TP_PROTO(int status), TP_ARGS(status)); > > [...] > > trace_mytacepoint(status); > > /* In a file registering this tracepoint */ > > int my_callback(int status, void *data) > { > struct my_struct my_data = data; > [...] > } > > [...] > my_data = kmalloc(sizeof(*my_data), GFP_KERNEL); > init_my_data(my_data); > register_trace_mytracepoint_data(my_callback, my_data); > > The same callback can also be registered to the same tracepoint as long > as the data registered is the same. Note, the data must also be used > to unregister the callback: > > unregister_trace_mytracepoint_data(my_callback, my_data); > > Because of the data parameter, tracepoints declared this way can not have > no args. That is: > > DECLARE_TRACE_DATA(mytracepoint, TP_PROTO(void), TP_ARGS()); > > will cause an error, but the original DECLARE_TRACE still allows for this. > > The DECLARE_TRACE_DATA() will be used by TRACE_EVENT() so that it > can reuse code and bring the size of the tracepoint footprint down. > This means that TRACE_EVENT()s must have at least one argument defined. We have to define at least on argument in TRACE_EVENT() even without this patch, otherwise it'll cause compile error while expanding the macros. > This should not be a problem since we should never have a static > tracepoint in the kernel that simply says "Look I'm here!". > We do have such a tracepoint. ;) That is trace_power_end, and it uses a dummy argument merely for passing compilation. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Steven Rostedt on 27 Apr 2010 11:30 On Tue, 2010-04-27 at 17:08 +0800, Li Zefan wrote: > Steven Rostedt wrote: > > Because of the data parameter, tracepoints declared this way can not have > > no args. That is: > > > > DECLARE_TRACE_DATA(mytracepoint, TP_PROTO(void), TP_ARGS()); > > > > will cause an error, but the original DECLARE_TRACE still allows for this. > > > > The DECLARE_TRACE_DATA() will be used by TRACE_EVENT() so that it > > can reuse code and bring the size of the tracepoint footprint down. > > This means that TRACE_EVENT()s must have at least one argument defined. > > We have to define at least on argument in TRACE_EVENT() even without > this patch, otherwise it'll cause compile error while expanding the > macros. OK, good to know that this is not a regression. The DECLARE_TRACE() still allows now arguments, I spent a bit of time (more than I wanted to) to make that work. Since I added a new DECLARE_TRACE_DATA() that must have at least one argument, it is not a regression, because it is new :-) Thanks, -- Steve P.S. I'll let these patches sit out for a week waiting for comments, and if there are none, I'll repackage them (rebase as well) and send them out for real. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Steven Rostedt on 28 Apr 2010 20:00 On Wed, 2010-04-28 at 16:37 -0400, Mathieu Desnoyers wrote: > * Steven Rostedt (rostedt(a)goodmis.org) wrote: > > From: Steven Rostedt <srostedt(a)redhat.com> > > > > This patch allows data to be passed to the tracepoint callbacks > > if the tracepoint was created to do so. > > > > If a tracepoint is defined with: > > > > DECLARE_TRACE_DATA(name, proto, args) > > > > Then a registered function can also register data to be passed > > to the tracepoint as such: > > > > DECLARE_TRACE_DATA(mytracepoint, TP_PROTO(int status), TP_ARGS(status)); > > > > /* In the C file */ > > > > DEFINE_TRACE(mytracepoint, TP_PROTO(int status), TP_ARGS(status)); > > > > [...] > > > > trace_mytacepoint(status); > > > > /* In a file registering this tracepoint */ > > > > int my_callback(int status, void *data) > > { > > struct my_struct my_data = data; > > [...] > > } > > > > [...] > > my_data = kmalloc(sizeof(*my_data), GFP_KERNEL); > > init_my_data(my_data); > > register_trace_mytracepoint_data(my_callback, my_data); > > > > The same callback can also be registered to the same tracepoint as long > > as the data registered is the same. Note, the data must also be used > > to unregister the callback: > > > > unregister_trace_mytracepoint_data(my_callback, my_data); > > > > Because of the data parameter, tracepoints declared this way can not have > > no args. That is: > > > > DECLARE_TRACE_DATA(mytracepoint, TP_PROTO(void), TP_ARGS()); > > > > will cause an error, but the original DECLARE_TRACE still allows for this. > > > > The DECLARE_TRACE_DATA() will be used by TRACE_EVENT() so that it > > can reuse code and bring the size of the tracepoint footprint down. > > This means that TRACE_EVENT()s must have at least one argument defined. > > This should not be a problem since we should never have a static > > tracepoint in the kernel that simply says "Look I'm here!". > > > > I'm not convinced DECLARE_TRACE_DATA() is an appropriate name. Sounds > confusing. What kind of data is this ? It is not obvious that this > refers to callback private data. Well, looking at the examples, it's pretty obvious what data is ;-) > > Why can't we just extend the existing DECLARE_TRACE() instead and add a > "callback_data" argument (or something slightly less verbose) ? We can > update all users anyway. > > We can also create a variant when there are no arguments passed: > > DECLARE_TRACE_NOARG() I have no problem with modifying DECLARE_TRACE() this way. In fact that was the original way I did it. I was just concerned about changing the fact that DECLARE_TRACE() no longer allows for (void), and it breaks your example in the samples dir. We can make DECLARE_TRACE() add the callback data, and add a NOARG() version for those that do not have any args. > > We had to do the same for the Linux kernel markers in the past. Then we > can create a TRACE_EVENT_NOARG() macro if necessary. Hmm, this may be difficult, since the TRACE_EVENT() requires passing of a arg. I guess we can make NOARG will just ignore the "arg" value. > > I don't think it makes sense to require users to pass arguments. It > should be possible to just say "I'm here". Cases where this could make > sense includes cases where we'd only be interested in global variables > at a specific tracepoint. Well, as Li just pointed out, we already require it ;-) Not a big deal, we can add a noarg version in the future, but this is the cost for doing advance work with CPP. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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