Re: [PATCH v1 1/5] perf/core: Define the common branch type classification

Arnaldo Carvalho de Melo
2017-04-04T14:18:14Z

Adding the perf kernel maintainers to the CC list.

Em Fri, Mar 31, 2017 at 11:18:38PM +0800, Jin Yao escreveu:
> It is often useful to know the branch types while analyzing branch
> data. For example, a call is very different from a conditional branch.
>
> Currently we have to look it up in binary while the binary may later
> not be available and even the binary is available but user has to take
> some time. It is very useful for user to check it directly in perf
> report.
>
> Perf already has support for disassembling the branch instruction
> to get the branch type. The branch type is defined in lbr.c.
>
> To keep consistent on kernel and userspace and make the classification
> more common, the patch adds the common branch type classification
> in perf_event.h.
>
> Since the disassembling of branch instruction needs some overhead,
> a new PERF_SAMPLE_BRANCH_TYPE_SAVE is introduced to indicate if it
> needs to disassemble the branch instruction and record the branch
> type.
>
> Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
> ---
> include/uapi/linux/perf_event.h | 24 +++++++++++++++++++++++-
> tools/include/uapi/linux/perf_event.h | 24 +++++++++++++++++++++++-
> 2 files changed, 46 insertions(+), 2 deletions(-)
>
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index d09a9cd..4d731fd 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -174,6 +174,8 @@ enum perf_branch_sample_type_shift {
> PERF_SAMPLE_BRANCH_NO_FLAGS_SHIFT = 14, /* no flags */
> PERF_SAMPLE_BRANCH_NO_CYCLES_SHIFT = 15, /* no cycles */
>
> + PERF_SAMPLE_BRANCH_TYPE_SAVE_SHIFT = 16, /* save branch type */
> +
> PERF_SAMPLE_BRANCH_MAX_SHIFT /* non-ABI */
> };
>
> @@ -198,9 +200,27 @@ enum perf_branch_sample_type {
> PERF_SAMPLE_BRANCH_NO_FLAGS = 1U << PERF_SAMPLE_BRANCH_NO_FLAGS_SHIFT,
> PERF_SAMPLE_BRANCH_NO_CYCLES = 1U << PERF_SAMPLE_BRANCH_NO_CYCLES_SHIFT,
>
> + PERF_SAMPLE_BRANCH_TYPE_SAVE =
> + 1U << PERF_SAMPLE_BRANCH_TYPE_SAVE_SHIFT,
> +
> PERF_SAMPLE_BRANCH_MAX = 1U << PERF_SAMPLE_BRANCH_MAX_SHIFT,
> };
>
> +/*
> + * Common flow change classification
> + */
> +enum {
> + PERF_BR_NONE = 0, /* unknown */
> + PERF_BR_JCC_FWD = 1 << 1, /* conditional forward jump */
> + PERF_BR_JCC_BWD = 1 << 2, /* conditional backward jump */
> + PERF_BR_JMP = 1 << 3, /* jump */
> + PERF_BR_IND_JMP = 1 << 4, /* indirect jump */
> + PERF_BR_CALL = 1 << 5, /* call */
> + PERF_BR_IND_CALL = 1 << 6, /* indirect call */
> + PERF_BR_RET = 1 << 7, /* return */
> + PERF_BR_FAR_BRANCH = 1 << 8, /* SYSCALL,SYSRET,IRQ,... */

Humm, wouldn't be better to have those in separate buckets? I.e.

PERF_BR_SYSCALL
PERF_BR_SYSRET,
PERF_BR_IRQ

etc?

And why a bitmask? /me reads a bit more... couldn't find a reason for
this:

+ type:9, /* branch type */

Do you have a reason to use 9 bits? Why not just:

enum {
PERF_BR_NONE = 0, /* unknown */
PERF_BR_JCC_FWD = 1, /* conditional forward jump */
PERF_BR_JCC_BWD = 2, /* conditional backward jump */
PERF_BR_JMP = 3, /* jump */
PERF_BR_IND_JMP = 4, /* indirect jump */
PERF_BR_CALL = 5, /* call */
PERF_BR_IND_CALL = 6, /* indirect call */
PERF_BR_RET = 7, /* return */
PERF_BR_FAR_BRANCH = 8, /* SYSCALL,SYSRET,IRQ,... */

And then use, say, 4 or 5 bits for that type field?

I must be missing something trivial ;-\

- Arnaldo

> +};
> +
> #define PERF_SAMPLE_BRANCH_PLM_ALL \
> (PERF_SAMPLE_BRANCH_USER|\
> PERF_SAMPLE_BRANCH_KERNEL|\
> @@ -999,6 +1019,7 @@ union perf_mem_data_src {
> * in_tx: running in a hardware transaction
> * abort: aborting a hardware transaction
> * cycles: cycles from last branch (or 0 if not supported)
> + * type: branch type
> */
> struct perf_branch_entry {
> __u64 from;
> @@ -1008,7 +1029,8 @@ struct perf_branch_entry {
> in_tx:1, /* in transaction */
> abort:1, /* transaction abort */
> cycles:16, /* cycle count to last branch */
> - reserved:44;
> + type:9, /* branch type */
> + reserved:35;
> };
>
> #endif /* _UAPI_LINUX_PERF_EVENT_H */
> diff --git a/tools/include/uapi/linux/perf_event.h b/tools/include/uapi/linux/perf_event.h
> index d09a9cd..4d731fd 100644
> --- a/tools/include/uapi/linux/perf_event.h
> +++ b/tools/include/uapi/linux/perf_event.h
> @@ -174,6 +174,8 @@ enum perf_branch_sample_type_shift {
> PERF_SAMPLE_BRANCH_NO_FLAGS_SHIFT = 14, /* no flags */
> PERF_SAMPLE_BRANCH_NO_CYCLES_SHIFT = 15, /* no cycles */
>
> + PERF_SAMPLE_BRANCH_TYPE_SAVE_SHIFT = 16, /* save branch type */
> +
> PERF_SAMPLE_BRANCH_MAX_SHIFT /* non-ABI */
> };
>
> @@ -198,9 +200,27 @@ enum perf_branch_sample_type {
> PERF_SAMPLE_BRANCH_NO_FLAGS = 1U << PERF_SAMPLE_BRANCH_NO_FLAGS_SHIFT,
> PERF_SAMPLE_BRANCH_NO_CYCLES = 1U << PERF_SAMPLE_BRANCH_NO_CYCLES_SHIFT,
>
> + PERF_SAMPLE_BRANCH_TYPE_SAVE =
> + 1U << PERF_SAMPLE_BRANCH_TYPE_SAVE_SHIFT,
> +
> PERF_SAMPLE_BRANCH_MAX = 1U << PERF_SAMPLE_BRANCH_MAX_SHIFT,
> };
>
> +/*
> + * Common flow change classification
> + */
> +enum {
> + PERF_BR_NONE = 0, /* unknown */
> + PERF_BR_JCC_FWD = 1 << 1, /* conditional forward jump */
> + PERF_BR_JCC_BWD = 1 << 2, /* conditional backward jump */
> + PERF_BR_JMP = 1 << 3, /* jump */
> + PERF_BR_IND_JMP = 1 << 4, /* indirect jump */
> + PERF_BR_CALL = 1 << 5, /* call */
> + PERF_BR_IND_CALL = 1 << 6, /* indirect call */
> + PERF_BR_RET = 1 << 7, /* return */
> + PERF_BR_FAR_BRANCH = 1 << 8, /* SYSCALL,SYSRET,IRQ,... */
> +};
> +
> #define PERF_SAMPLE_BRANCH_PLM_ALL \
> (PERF_SAMPLE_BRANCH_USER|\
> PERF_SAMPLE_BRANCH_KERNEL|\
> @@ -999,6 +1019,7 @@ union perf_mem_data_src {
> * in_tx: running in a hardware transaction
> * abort: aborting a hardware transaction
> * cycles: cycles from last branch (or 0 if not supported)
> + * type: branch type
> */
> struct perf_branch_entry {
> __u64 from;
> @@ -1008,7 +1029,8 @@ struct perf_branch_entry {
> in_tx:1, /* in transaction */
> abort:1, /* transaction abort */
> cycles:16, /* cycle count to last branch */
> - reserved:44;
> + type:9, /* branch type */
> + reserved:35;
> };
>
> #endif /* _UAPI_LINUX_PERF_EVENT_H */
> --
> 2.7.4