Messages in this thread Patch in this message | | | Date | Thu, 10 Dec 2009 09:27:19 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] perf sched: Add max delay time snapshot |
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* Xiao Guangrong <xiaoguangrong@cn.fujitsu.com> wrote:
> > > Ingo Molnar wrote: > > * Xiao Guangrong <xiaoguangrong@cn.fujitsu.com> wrote: > > > >> Frederic Weisbecker wrote: > >> > >>> When we have a maximum latency reported for a task, we need a > >>> convenient way to find the matching location to the raw traces or to > >>> perf sched map that shows where the task has been eventually > >>> scheduled in. This gives a pointer to retrieve the events that > >>> occured during this max latency. > >> Then, we can cooperate with ftrace's data to know what the cpu is > >> doing at that time. > > > > What do you mean by mixing it with ftrace data? These events ought to be > > a full replacement for the sched and wakeup tracers. In the long run we > > want a single stream of events and phase out most of the pretty-printing > > ftrace plugins. > > Hi Ingo, > > I think sometimes perf tool cooperate with ftrace can do more useful > things, take this case for example: > > By 'perf sched latency' we can get the schedule latency time, if the > time is abnormal, then we can run this command and enable function > tracer. > > After running, 'perf sched latency' can show us the timestamps when > the maximum latency(the worst case) occurs, then we can find what the > cpu is doing at this timestamps by reading function tracer's output.
Actually, i think the natural solution here is not any ugly interaction between two largely disjunct sets of APIs, but a new feature: to turn the function tracer into an event.
That would allow perf sched to also record function traces if so desired. And it would also allow a whole lot of other things - mixing function tracer events and other events.
As a starter we could create a new function tracer event. A crude prototype hack is attached below - via that it should already be possible to 'count' function calls via:
perf stat -a --repeat 3 -e context-switches sleep 1
( obviously the real patch would introduce PERF_COUNT_SW_FUNCTION_CALLS, but you get the point. )
Ingo
--- include/trace/events/function.h | 33 +++++++++++++++++++++++++++++++++ kernel/trace/ftrace.c | 15 +++++++++++++++ 2 files changed, 48 insertions(+)
Index: linux/include/trace/events/function.h =================================================================== --- /dev/null +++ linux/include/trace/events/function.h @@ -0,0 +1,33 @@ +#undef TRACE_SYSTEM +#define TRACE_SYSTEM function + +#if !defined(_TRACE_FUNCTION_H) || defined(TRACE_HEADER_MULTI_READ) +#define _TRACE_FUNCTION_H + +#include <linux/tracepoint.h> + +TRACE_EVENT(function_call, + + TP_PROTO(unsigned long ip, unsigned long parent_ip), + + TP_ARGS(ip, parent_ip), + + TP_STRUCT__entry( + __field( u64, ip ) + __field( u64, parent_ip ) + ), + + TP_fast_assign( + __entry->ip = ip; + __entry->parent_ip = parent_ip; + ), + + TP_printk("IP: %016Lx, parent IP: %016Lx", + __entry->ip, + __entry->parent_ip) +); + +#endif /* _TRACE_FUNCTION_H */ + +/* This part must be outside protection */ +#include <trace/define_trace.h> Index: linux/kernel/trace/ftrace.c =================================================================== --- linux.orig/kernel/trace/ftrace.c +++ linux/kernel/trace/ftrace.c @@ -2769,9 +2769,24 @@ void __init ftrace_init(void) #else +#define CREATE_TRACE_POINTS +#include <trace/events/function.h> + +static void perf_ftrace_func(unsigned long ip, unsigned long parent_ip) +{ + struct pt_regs *regs = task_pt_regs(current); + + perf_sw_event(PERF_COUNT_SW_CONTEXT_SWITCHES, 1, 1, regs, 0); +} + static int __init ftrace_nodyn_init(void) { ftrace_enabled = 1; + + printk("enabling function tracer test\n"); + + ftrace_trace_function = perf_ftrace_func; + return 0; } device_initcall(ftrace_nodyn_init);
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