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    SubjectRe: [PATCH] perfcounters: Support for ftrace event records sampling
    On Fri, Aug 07, 2009 at 12:37:57PM +0200, Peter Zijlstra wrote:
    > On Fri, 2009-08-07 at 01:25 +0200, Frederic Weisbecker wrote:
    > > This patch brings the kernel side support for ftrace event record
    > > sampling.
    > >
    > > A new counter attribute is added: PERF_SAMPLE_TP_RECORD which requests
    > > ftrace events record sampling.
    > >
    >
    > > + PERF_SAMPLE_TP_RECORD = 1U << 10,
    >
    > I'd really want this thing called PERF_SAMPLE_RAW
    >
    > > - PERF_SAMPLE_MAX = 1U << 10, /* non-ABI */
    > > + PERF_SAMPLE_MAX = 1U << 11, /* non-ABI */
    > > };
    > >
    > > /*
    > > @@ -413,6 +414,11 @@ struct perf_callchain_entry {
    > > __u64 ip[PERF_MAX_STACK_DEPTH];
    > > };
    > >
    > > +struct perf_tracepoint_record {
    > > + int size;
    > > + char *record;
    > > +};
    >
    > Which would make this:
    >
    > struct perf_raw_record {
    > u32 size;
    > void *data;
    > };
    >
    > > struct task_struct;
    > >
    > > /**
    > > @@ -681,6 +687,7 @@ struct perf_sample_data {
    > > struct pt_regs *regs;
    > > u64 addr;
    > > u64 period;
    > > + void *private;
    > > };
    >
    > might as well make that struct perf_raw_record *raw;



    Ok. Yeah that's far more generic (and typed).


    >
    > > @@ -649,5 +617,99 @@ __attribute__((section("_ftrace_events"))) event_##call = { \
    > >
    > > #include TRACE_INCLUDE(TRACE_INCLUDE_FILE)
    > >
    > > +/*
    > > + * Define the insertion callback to profile events
    > > + *
    > > + * The job is very similar to ftrace_raw_event_<call> except that we don't
    > > + * insert in the ring buffer but in a perf counter.
    > > + *
    > > + * static void ftrace_profile_<call>(proto)
    > > + * {
    > > + * struct ftrace_data_offsets_<call> __maybe_unused __data_offsets;
    > > + * struct ftrace_event_call *event_call = &event_<call>;
    > > + * extern void perf_tpcounter_event(int, u64, u64, void *, int);
    > > + * struct ftrace_raw_##call *entry;
    > > + * u64 __addr = 0, __count = 1;
    > > + * unsigned long irq_flags;
    > > + * int __entry_size;
    > > + * int __data_size;
    > > + * int pc;
    > > + *
    > > + * local_save_flags(irq_flags);
    > > + * pc = preempt_count();
    > > + *
    > > + * __data_size = ftrace_get_offsets_<call>(&__data_offsets, args);
    > > + * __entry_size = __data_size + sizeof(*entry);
    > > + *
    > > + * do {
    > > + * char raw_data[__entry_size]; <- allocate our sample in the stack
    > > + * struct trace_entry *ent;
    > > + *
    > > + * entry = (struct ftrace_raw_<call> *)raw_data;
    > > + * ent = &entry->ent;
    > > + * tracing_generic_entry_update(ent, irq_flags, pc);
    > > + * ent->type = event_call->id;
    > > + *
    > > + * <tstruct> <- do some jobs with dynamic arrays
    > > + *
    > > + * <assign> <- affect our values
    > > + *
    > > + * perf_tpcounter_event(event_call->id, __addr, __count, entry,
    > > + * __entry_size); <- submit them to perf counter
    > > + * } while (0);
    > > + *
    > > + * }
    > > + */
    > > +
    > > +#ifdef CONFIG_EVENT_PROFILE
    > > +
    > > +#undef __perf_addr
    > > +#define __perf_addr(a) __addr = (a)
    > > +
    > > +#undef __perf_count
    > > +#define __perf_count(c) __count = (c)
    > > +
    > > +#undef TRACE_EVENT
    > > +#define TRACE_EVENT(call, proto, args, tstruct, assign, print) \
    > > +static void ftrace_profile_##call(proto) \
    > > +{ \
    > > + struct ftrace_data_offsets_##call __maybe_unused __data_offsets;\
    > > + struct ftrace_event_call *event_call = &event_##call; \
    > > + extern void perf_tpcounter_event(int, u64, u64, void *, int); \
    > > + struct ftrace_raw_##call *entry; \
    > > + u64 __addr = 0, __count = 1; \
    > > + unsigned long irq_flags; \
    > > + int __entry_size; \
    > > + int __data_size; \
    > > + int pc; \
    > > + \
    > > + local_save_flags(irq_flags); \
    > > + pc = preempt_count(); \
    > > + \
    > > + __data_size = ftrace_get_offsets_##call(&__data_offsets, args); \
    > > + __entry_size = __data_size + sizeof(*entry); \
    > > + \
    > > + do { \
    > > + char raw_data[__entry_size]; \
    > > + struct trace_entry *ent; \
    > > + \
    > > + entry = (struct ftrace_raw_##call *)raw_data; \
    > > + ent = &entry->ent; \
    > > + tracing_generic_entry_update(ent, irq_flags, pc); \
    > > + ent->type = event_call->id; \
    > > + \
    > > + tstruct \
    > > + \
    > > + { assign; } \
    > > + \
    > > + perf_tpcounter_event(event_call->id, __addr, __count, entry,\
    > > + __entry_size); \
    > > + } while (0); \
    > > + \
    > > +}
    >
    > ok, so the one concern I have here is that the data needs to fit on the
    > stack. What if someone puts a large string in the data?



    Yeah, I'll try to fix this by storing strings as pointers and copy
    them in perf counter output only.

    TODO-listed, with all the above.



    > > +
    > > +#include TRACE_INCLUDE(TRACE_INCLUDE_FILE)
    > > +#endif /* CONFIG_EVENT_PROFILE */
    > > +
    > > #undef _TRACE_PROFILE_INIT
    > >
    > > diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
    > > index 06d210c..93f4312 100644
    > > --- a/kernel/perf_counter.c
    > > +++ b/kernel/perf_counter.c
    > > @@ -2646,6 +2646,7 @@ static void perf_counter_output(struct perf_counter *counter, int nmi,
    > > u64 counter;
    > > } group_entry;
    > > struct perf_callchain_entry *callchain = NULL;
    > > + struct perf_tracepoint_record *tp;
    > > int callchain_size = 0;
    > > u64 time;
    > > struct {
    > > @@ -2714,6 +2715,11 @@ static void perf_counter_output(struct perf_counter *counter, int nmi,
    > > header.size += sizeof(u64);
    > > }
    > >
    > > + if (sample_type & PERF_SAMPLE_TP_RECORD) {
    > > + tp = data->private;
    > > + header.size += tp->size;
    > > + }
    > > +
    > > ret = perf_output_begin(&handle, counter, header.size, nmi, 1);
    > > if (ret)
    > > return;
    > > @@ -2777,6 +2783,9 @@ static void perf_counter_output(struct perf_counter *counter, int nmi,
    > > }
    > > }
    > >
    > > + if (sample_type & PERF_SAMPLE_TP_RECORD)
    > > + perf_output_copy(&handle, tp->record, tp->size);
    > > +
    > > perf_output_end(&handle);
    > > }
    >
    > You seem to fail to round up to a multiple of u64 somewhere along the
    > line, that'll mess things up as events are supposed to be u64 aligned.


    Indeed.



    >
    > > diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
    > > index 6da0992..90c9808 100644
    > > --- a/tools/perf/builtin-record.c
    > > +++ b/tools/perf/builtin-record.c
    > > @@ -412,6 +412,7 @@ static void create_counter(int counter, int cpu, pid_t pid)
    > > if (call_graph)
    > > attr->sample_type |= PERF_SAMPLE_CALLCHAIN;
    > >
    > > +
    > > attr->mmap = track;
    > > attr->comm = track;
    > > attr->inherit = (cpu < 0) && inherit;
    >
    > Do we really need that extra whitespace?


    Sorry, I added the explicit PERF_SAMPLE_TP_RECORD here to test this patch
    and forgot the newline when I removed it :-s



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