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

[Namhyung Kim]

Ping!

On Tue, Jun 7, 2016 at 10:49 PM, Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
> Hi Steve,
>
> Could you please take a look at this?
>
> Thanks,
> Namhyung
>
>
> On Mon, May 23, 2016 at 12:26 AM, Namhyung Kim <namhyung@xxxxxxxxxx> 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@xxxxxxxxxx>
>> ---
>>  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