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Date: Thu, 14 May 2009 22:33:53 +0200
From: Frederic Weisbecker <fweisbec@...il.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
Christoph Hellwig <hch@...radead.org>,
Ingo Molnar <mingo@...e.hu>,
Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC] tracing: adding flags to events
On Thu, May 14, 2009 at 03:45:48PM -0400, Steven Rostedt wrote:
>
> Christoph has been asking about processing flags in the output. He rather
> not see c2, and rather see what those three bits are. This patch is
> an RFC to do just that. To test it out, I added the previous task state to
> sched switch and used the flag processing to the printk of the
> sched_switch event.
>
>
> To add a flag, just add __print_flags to the TP_printk arguments.
>
> TP_STRUCT__entry(
> __field( unsigned int, flags )
> ),
>
> TP_printk("flags are %s", __print_flags(__entry->flags,
> 0, "BIT0", 1, "BIT1", 2, "BIT2", -1))
>
Nice idea!
Also, I wonder if that would be possible to get compounded
bits such as GFP_KERNEL instead of __GFP_WAIT | __GFP_IO | __GFP_FS.
To perform that, we could just add two fields:
//__b for byte, __m for mask
#define __b(b) (1 << b)
#define __m(m) m
And then you can compare using a mask.
It also requires to clear the mask from the flags to avoid
duplicate matches such as GFP_KERNEL | __GFP_WAIT | __GFP_IO | __GFP_FS
and only have GFP_KERNEL, eg:
const char *
ftrace_print_flags_seq(struct trace_seq *p, unsigned long flags, ...)
{
const char *str;
va_list args;
long mask;
trace_seq_init(p);
va_start(args, flags);
for (mask = va_arg(args, long) ; mask >= 0; mask = va_arg(args, long)) {
str = va_arg(args, const char *);
if (flags & mask != mask)
continue;
flags &= ~mask;
if (p->len)
trace_seq_putc(p, '|');
trace_seq_puts(p, str);
}
va_end(args);
trace_seq_putc(p, 0);
return p->buffer;
}
> Thus __print_flags prototype would look like:
>
> const char *__print_flags(long flags, ...);
>
> But it is actually converted to other helper functions to handle the
> string. The trick that ftrace does, is disables preemption before calling
> the printk, uses a percpu buffer, and passes that in to a helper function
> that will print out the flags.
>
> You could see "flags are BIT1|BIT2" if flags was 6 in the above case.
>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
> index bae51dd..10da87a 100644
> --- a/include/linux/ftrace_event.h
> +++ b/include/linux/ftrace_event.h
> @@ -3,12 +3,16 @@
>
> #include <linux/trace_seq.h>
> #include <linux/ring_buffer.h>
> -
> +#include <linux/percpu.h>
>
> struct trace_array;
> struct tracer;
> struct dentry;
>
> +DECLARE_PER_CPU(struct trace_seq, ftrace_event_seq);
> +const char *ftrace_print_flags_seq(struct trace_seq *p,
> + unsigned long flags, ...);
> +
> /*
> * The trace entry - the most basic unit of tracing. This is what
> * is printed in the end as a single line in the trace output, such as:
> diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
> index dd4033c..b4fcd40 100644
> --- a/include/trace/events/sched.h
> +++ b/include/trace/events/sched.h
> @@ -156,6 +156,7 @@ TRACE_EVENT(sched_switch,
> __array( char, prev_comm, TASK_COMM_LEN )
> __field( pid_t, prev_pid )
> __field( int, prev_prio )
> + __field( long, prev_state )
> __array( char, next_comm, TASK_COMM_LEN )
> __field( pid_t, next_pid )
> __field( int, next_prio )
> @@ -165,13 +166,18 @@ TRACE_EVENT(sched_switch,
> memcpy(__entry->next_comm, next->comm, TASK_COMM_LEN);
> __entry->prev_pid = prev->pid;
> __entry->prev_prio = prev->prio;
> + __entry->prev_state = prev->state;
> memcpy(__entry->prev_comm, prev->comm, TASK_COMM_LEN);
> __entry->next_pid = next->pid;
> __entry->next_prio = next->prio;
> ),
>
> - TP_printk("task %s:%d [%d] ==> %s:%d [%d]",
> + TP_printk("task %s:%d [%d] (%s) ==> %s:%d [%d]",
> __entry->prev_comm, __entry->prev_pid, __entry->prev_prio,
> + __entry->prev_state ?
> + __print_flags(__entry->prev_state,
> + 0, "S", 1, "D", 2, "T", 3, "t",
> + 4, "Z", 5, "X", 6, "x", 7, "W") : "R",
> __entry->next_comm, __entry->next_pid, __entry->next_prio)
> );
>
> diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
> index edb02bc..1b1e6e8 100644
> --- a/include/trace/ftrace.h
> +++ b/include/trace/ftrace.h
> @@ -87,6 +87,7 @@
> * struct trace_seq *s = &iter->seq;
> * struct ftrace_raw_<call> *field; <-- defined in stage 1
> * struct trace_entry *entry;
> + * struct trace_seq *p;
> * int ret;
> *
> * entry = iter->ent;
> @@ -98,7 +99,9 @@
> *
> * field = (typeof(field))entry;
> *
> + * p = get_cpu_var(ftrace_event_seq);
> * ret = trace_seq_printf(s, <TP_printk> "\n");
> + * put_cpu();
> * if (!ret)
> * return TRACE_TYPE_PARTIAL_LINE;
> *
> @@ -119,6 +122,8 @@
> #undef __get_str
> #define __get_str(field) ((char *)__entry + __entry->__str_loc_##field)
>
> +#define __print_flags(flag, x...) ftrace_print_flags_seq(p, flag, x)
> +
> #undef TRACE_EVENT
> #define TRACE_EVENT(call, proto, args, tstruct, assign, print) \
> enum print_line_t \
> @@ -127,6 +132,7 @@ ftrace_raw_output_##call(struct trace_iterator *iter, int flags) \
> struct trace_seq *s = &iter->seq; \
> struct ftrace_raw_##call *field; \
> struct trace_entry *entry; \
> + struct trace_seq *p; \
> int ret; \
> \
> entry = iter->ent; \
> @@ -138,7 +144,9 @@ ftrace_raw_output_##call(struct trace_iterator *iter, int flags) \
> \
> field = (typeof(field))entry; \
> \
> + p = &get_cpu_var(ftrace_event_seq); \
> ret = trace_seq_printf(s, #call ": " print); \
> + put_cpu(); \
I don't understand the role of this per-cpu trace_seq variable.
It doesn't seem to be used.
Frederic.
> if (!ret) \
> return TRACE_TYPE_PARTIAL_LINE; \
> \
> diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
> index 8bd9a2c..29af794 100644
> --- a/kernel/trace/trace_output.c
> +++ b/kernel/trace/trace_output.c
> @@ -14,6 +14,8 @@
> /* must be a power of 2 */
> #define EVENT_HASHSIZE 128
>
> +DEFINE_PER_CPU(struct trace_seq, ftrace_event_seq);
> +
> static DEFINE_MUTEX(trace_event_mutex);
> static struct hlist_head event_hash[EVENT_HASHSIZE] __read_mostly;
>
> @@ -212,6 +214,31 @@ int trace_seq_path(struct trace_seq *s, struct path *path)
> return 0;
> }
>
> +const char *
> +ftrace_print_flags_seq(struct trace_seq *p, unsigned long flags, ...)
> +{
> + const char *str;
> + va_list args;
> + long bit;
> +
> + trace_seq_init(p);
> + va_start(args, flags);
> + for (bit = va_arg(args, long) ; bit >= 0; bit = va_arg(args, long)) {
> + str = va_arg(args, const char *);
> +
> + if (!(flags & (1<<bit)))
> + continue;
> +
> + if (p->len)
> + trace_seq_putc(p, '|');
> + trace_seq_puts(p, str);
> + }
> + va_end(args);
> + trace_seq_putc(p, 0);
> +
> + return p->buffer;
> +}
> +
> #ifdef CONFIG_KRETPROBES
> static inline const char *kretprobed(const char *name)
> {
>
--
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