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Date: Fri, 7 Aug 2009 22:26:31 +0200
From: Frederic Weisbecker <fweisbec@...il.com>
To: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
Arnaldo Carvalho de Melo <acme@...hat.com>,
Mike Galbraith <efault@....de>,
Steven Rostedt <rostedt@...dmis.org>,
Paul Mackerras <paulus@...ba.org>,
Pekka Enberg <penberg@...helsinki.fi>,
Gabriel Munteanu <eduard.munteanu@...ux360.ro>,
Li Zefan <lizf@...fujitsu.com>,
Lai Jiangshan <laijs@...fujitsu.com>
Subject: Re: [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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