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Message-ID: <20100227115234.GG5130@nowhere>
Date: Sat, 27 Feb 2010 12:52:36 +0100
From: Frederic Weisbecker <fweisbec@...il.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
Andrew Morton <akpm@...ux-foundation.org>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Mathieu Desnoyers <compudj@...stal.dyndns.org>,
Lai Jiangshan <laijs@...fujitsu.com>,
Li Zefan <lizf@...fujitsu.com>, Christoph Hellwig <hch@....de>,
Wu Fengguang <fengguang.wu@...el.com>
Subject: Re: [PATCH 1/2 v2] tracing: Add EXTRACT_TRACE_SYMBOL() macro
On Fri, Feb 26, 2010 at 12:38:32AM -0500, Steven Rostedt wrote:
> The trace events that are created with the TRACE_EVENT family macros
> can be read by binary readers, such as perf and trace-cmd. In order
> to translate the binary data, the events also have a format file
> associated with them. This format file explains the offset, size and
> signedness of elements in the raw binary data of an event.
>
> At the end of the format file, there is a description on how to print
> this data. A helper function is used to map numbers into strings
> called __print_symbolic(). A problem arises when these numbers are
> defined as enums in the kernel. The macros that export this data into
> the format file does not translate the enums into numbers. Thus we
> have in the irq.h file:
>
> #define softirq_name(sirq) { sirq##_SOFTIRQ, #sirq }
> #define show_softirq_name(val) \
> __print_symbolic(val, \
> softirq_name(HI), \
> softirq_name(TIMER), \
> softirq_name(NET_TX), \
> softirq_name(NET_RX), \
> softirq_name(BLOCK), \
> softirq_name(BLOCK_IOPOLL), \
> softirq_name(TASKLET), \
> softirq_name(SCHED), \
> softirq_name(HRTIMER), \
> softirq_name(RCU))
>
>
> TP_printk("vec=%d [action=%s]", __entry->vec,
> show_softirq_name(__entry->vec))
>
>
> Which shows up in the event format file as:
>
> print fmt: "vec=%d [action=%s]", REC->vec, __print_symbolic(REC->vec, { HI_SOFTIRQ, "HI" }, { TIMER_SOFTIRQ, "TIMER" }, { NET_TX_SOFTIRQ, "NET_TX" }, { NET_RX_SOFTIRQ, "NET_RX" }, { BLOCK_SOFTIRQ, "BLOCK" }, { BLOCK_IOPOLL_SOFTIRQ, "BLOCK_IOPOLL" }, { TASKLET_SOFTIRQ, "TASKLET" }, { SCHED_SOFTIRQ, "SCHED" }, { HRTIMER_SOFTIRQ, "HRTIMER" }, { RCU_SOFTIRQ, "RCU" })
>
>
> The parser has no idea of how to translate "HI_SOFTIRQ" into a number.
>
> This patch adds an EXTRACT_TRACE_SYMBOLS() macro that lets a trace header
> define symbols that it uses, and will be converted into numbers.
> These symbols will be shown in an "event_symbols" file in the event
> directory.
>
> Enums that use this also need to be converted into the following format:
>
> #define ENUMS \
> C(ENUM1) \
> C(ENUM2) \
> C(ENUM3)
>
> #define C(name) name
> enum { ENUMS };
> #undef C
>
> Then the trace header can do the following:
>
> #define C(name) TRACE_SYMBOL_PARSE(#name, name, sizeof(name))
> EXTRACT_TRACE_SYMBOLS(mysyms, ENUMS)
>
> For example, for the softirq names we can now have:
>
> #define C(sirq) \
> TRACE_SYMBOL_PARSE(#sirq, sirq##_SOFTIRQ, sizeof(sirq##_SOFTIRQ))
>
> EXTRACT_TRACE_SYMBOLS(softirqs, SOFTIRQ_NAMES)
>
> where the SOFTIRQ_NAMES are defined as:
>
> #define SOFTIRQ_NAMES \
> C(HI), \
> C(TIMER), \
> C(NET_TX), \
> [...]
> C(RCU)
> #define C(name) name##_SOFTIRQ
> enum { SOFTIRQ_NAMES, NR_SOFTIRQS };
>
>
> This produces:
>
> [tracing/]$ cat events/event_symbols
> # Symbol:Size:Value
> # =================
> HI_SOFTIRQ:4:0
> TIMER_SOFTIRQ:4:1
> NET_TX_SOFTIRQ:4:2
> NET_RX_SOFTIRQ:4:3
> BLOCK_SOFTIRQ:4:4
> BLOCK_IOPOLL_SOFTIRQ:4:5
> TASKLET_SOFTIRQ:4:6
> SCHED_SOFTIRQ:4:7
> HRTIMER_SOFTIRQ:4:8
> RCU_SOFTIRQ:4:9
There is a risk of having a big mess in this file
if we have various types of enums inside. I mean,
it doesn't make the things easy for the tools as they will
have to iterate through the whole list and sort it out
using the suffixes (*_SOFTIRQ).
We could perhaps have this per event subsystem?
cat events/irq/event_symbols
> TRACE_PRINTKS() \
> Index: linux-trace.git/include/linux/tracepoint.h
> ===================================================================
> --- linux-trace.git.orig/include/linux/tracepoint.h 2010-02-12 13:35:15.000000000 -0500
> +++ linux-trace.git/include/linux/tracepoint.h 2010-02-25 22:47:10.000000000 -0500
> @@ -292,4 +292,6 @@ static inline void tracepoint_synchroniz
> assign, print, reg, unreg) \
> DECLARE_TRACE(name, PARAMS(proto), PARAMS(args))
>
> +#define EXTRACT_TRACE_SYMBOLS(name, symbols)
So this could also take the name of the subsystem.
> +
> #endif /* ifdef TRACE_EVENT (see note above) */
> Index: linux-trace.git/include/trace/define_trace.h
> ===================================================================
> --- linux-trace.git.orig/include/trace/define_trace.h 2010-02-12 13:35:15.000000000 -0500
> +++ linux-trace.git/include/trace/define_trace.h 2010-02-25 23:53:52.000000000 -0500
> @@ -20,6 +20,7 @@
> /* Prevent recursion */
> #undef CREATE_TRACE_POINTS
>
> +#include <trace/trace_syms.h>
> #include <linux/stringify.h>
>
> #undef TRACE_EVENT
> @@ -43,6 +44,20 @@
> #define DECLARE_TRACE(name, proto, args) \
> DEFINE_TRACE(name)
>
> +#undef EXTRACT_TRACE_SYMBOLS
> +#define EXTRACT_TRACE_SYMBOLS(name, symbols) \
> + struct trace_syms ___trace_sym_##name[] \
> + __attribute__((section("_trace_symbols"), aligned(4))) = { \
> + symbols \
> + }
> +
> +#define TRACE_SYMBOL_PARSE(symbol, value, sym_size) \
> + { \
> + .name = symbol, \
> + .val = (u64)(value), \
> + .size = sym_size \
...which could be appended there.
What do you think?
--
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