linux-kernel - Re: [RFC/PATCH] ftrace: Reduce size of function graph entries

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Date:	Tue, 7 Jun 2016 22:49:15 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC/PATCH] ftrace: Reduce size of function graph entries

Hi Steve,

Could you please take a look at this?

Thanks,
Namhyung


On Mon, May 23, 2016 at 12:26 AM, Namhyung Kim <namhyung@...nel.org> wrote:
> Currently ftrace_graph_ent{,_entry} and ftrace_graph_ret{,_entry} struct
> can have padding bytes at the end due to alignment in 64-bit data type.
> As these data are recorded so frequently, those paddings waste
> non-negligible space.  As some archs can have efficient unaligned
> accesses, reducing the alignment can save ~10% of data size:
>
>   ftrace_graph_ent_entry:  24 -> 20
>   ftrace_graph_ret_entry:  48 -> 44
>
> Also I moved the 'overrun' field in struct ftrace_graph_ret to minimize
> the padding.  Tested on x86_64 only.
>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
>  include/linux/ftrace.h       | 16 ++++++++++++----
>  kernel/trace/trace.h         | 11 +++++++++++
>  kernel/trace/trace_entries.h |  4 ++--
>  3 files changed, 25 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index dea12a6e413b..35c523ba5c59 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -751,25 +751,33 @@ extern void ftrace_init(void);
>  static inline void ftrace_init(void) { }
>  #endif
>
> +#ifndef CONFIG_HAVE_64BIT_ALIGNED_ACCESS
> +# define FTRACE_ALIGNMENT      4
> +#else
> +# define FTRACE_ALIGNMENT      8
> +#endif
> +
> +#define FTRACE_ALIGN_DATA      __attribute__((packed, aligned(FTRACE_ALIGNMENT)))
> +
>  /*
>   * Structure that defines an entry function trace.
>   */
>  struct ftrace_graph_ent {
>         unsigned long func; /* Current function */
>         int depth;
> -};
> +} FTRACE_ALIGN_DATA;
>
>  /*
>   * Structure that defines a return function trace.
>   */
>  struct ftrace_graph_ret {
>         unsigned long func; /* Current function */
> -       unsigned long long calltime;
> -       unsigned long long rettime;
>         /* Number of functions that overran the depth limit for current task */
>         unsigned long overrun;
> +       unsigned long long calltime;
> +       unsigned long long rettime;
>         int depth;
> -};
> +} FTRACE_ALIGN_DATA;
>
>  /* Type of the callback handlers for tracing function graph*/
>  typedef void (*trace_func_graph_ret_t)(struct ftrace_graph_ret *); /* return */
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 5167c366d6b7..d2dd49ca55ee 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -80,6 +80,12 @@ enum trace_type {
>         FTRACE_ENTRY(name, struct_name, id, PARAMS(tstruct), PARAMS(print), \
>                      filter)
>
> +#undef FTRACE_ENTRY_PACKED
> +#define FTRACE_ENTRY_PACKED(name, struct_name, id, tstruct, print,     \
> +                           filter)                                     \
> +       FTRACE_ENTRY(name, struct_name, id, PARAMS(tstruct), PARAMS(print), \
> +                    filter) FTRACE_ALIGN_DATA
> +
>  #include "trace_entries.h"
>
>  /*
> @@ -1600,6 +1606,11 @@ int set_tracer_flag(struct trace_array *tr, unsigned int mask, int enabled);
>  #define FTRACE_ENTRY_DUP(call, struct_name, id, tstruct, print, filter)        \
>         FTRACE_ENTRY(call, struct_name, id, PARAMS(tstruct), PARAMS(print), \
>                      filter)
> +#undef FTRACE_ENTRY_PACKED
> +#define FTRACE_ENTRY_PACKED(call, struct_name, id, tstruct, print, filter) \
> +       FTRACE_ENTRY(call, struct_name, id, PARAMS(tstruct), PARAMS(print), \
> +                    filter)
> +
>  #include "trace_entries.h"
>
>  #if defined(CONFIG_PERF_EVENTS) && defined(CONFIG_FUNCTION_TRACER)
> diff --git a/kernel/trace/trace_entries.h b/kernel/trace/trace_entries.h
> index ee7b94a4810a..5c30efcda5e6 100644
> --- a/kernel/trace/trace_entries.h
> +++ b/kernel/trace/trace_entries.h
> @@ -72,7 +72,7 @@ FTRACE_ENTRY_REG(function, ftrace_entry,
>  );
>
>  /* Function call entry */
> -FTRACE_ENTRY(funcgraph_entry, ftrace_graph_ent_entry,
> +FTRACE_ENTRY_PACKED(funcgraph_entry, ftrace_graph_ent_entry,
>
>         TRACE_GRAPH_ENT,
>
> @@ -88,7 +88,7 @@ FTRACE_ENTRY(funcgraph_entry, ftrace_graph_ent_entry,
>  );
>
>  /* Function return entry */
> -FTRACE_ENTRY(funcgraph_exit, ftrace_graph_ret_entry,
> +FTRACE_ENTRY_PACKED(funcgraph_exit, ftrace_graph_ret_entry,
>
>         TRACE_GRAPH_RET,
>
> --
> 2.8.0
>



-- 
Thanks,
Namhyung