Re: [PATCH] perfcounters: Support for ftrace event records sampling
From: Peter Zijlstra
Date: Fri Aug 07 2009 - 06:38:25 EST
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;
> @@ -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?
> +
> +#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.
> 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?
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