Re: [PATCH v4 1/5] perf cs-etm: Refactor instruction size handling

[Mike Leach]

Hi Leo,

On Mon, 3 Feb 2020 at 02:07, Leo Yan <leo.yan@xxxxxxxxxx> wrote:
>
> cs-etm.c has several functions which need to know instruction size
> based on address, e.g. cs_etm__instr_addr() and cs_etm__copy_insn()
> two functions both calculate the instruction size separately with its
> duplicated code.  Furthermore, adding new features later which might
> require to calculate instruction size as well.
>
> For this reason, this patch refactors the code to introduce a new
> function cs_etm__instr_size(), this function is central place to
> calculate the instruction size based on ISA type and instruction
> address.
>
> For a neat implementation, cs_etm__instr_addr() will always execute the
> loop without checking ISA type, this allows cs_etm__instr_size() and
> cs_etm__instr_addr() have no any duplicate code with each other and both
> functions are independent and can be changed separately without breaking
> anything.  As a side effect, cs_etm__instr_addr() will do a few more
> iterations for A32/A64 instructions, this would be fine if consider perf
> is a tool running in the user space.
>

I prefer to take the optimisation win where I can - I always do in the
trace decoder when counting instructions over a range.
Consider that you can be processing MB of trace data, and most likely
that will be A64/A32 on a lot of the current and future platforms.

Therefore I would keep the useful cs_etm__instr_size() function, but
also keep a single ISA check in cs_etm__instr_addr() to do
the (addr + offset * 4) calculation for non T32.

Regards

Mike

> Signed-off-by: Leo Yan <leo.yan@xxxxxxxxxx>
> ---
>  tools/perf/util/cs-etm.c | 48 +++++++++++++++++++++++-----------------
>  1 file changed, 28 insertions(+), 20 deletions(-)
>
> diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> index 720108bd8dba..cb6fcc2acca0 100644
> --- a/tools/perf/util/cs-etm.c
> +++ b/tools/perf/util/cs-etm.c
> @@ -918,6 +918,26 @@ static inline int cs_etm__t32_instr_size(struct cs_etm_queue *etmq,
>         return ((instrBytes[1] & 0xF8) >= 0xE8) ? 4 : 2;
>  }
>
> +static inline int cs_etm__instr_size(struct cs_etm_queue *etmq,
> +                                    u8 trace_chan_id,
> +                                    enum cs_etm_isa isa,
> +                                    u64 addr)
> +{
> +       int insn_len;
> +
> +       /*
> +        * T32 instruction size might be 32-bit or 16-bit, decide by calling
> +        * cs_etm__t32_instr_size().
> +        */
> +       if (isa == CS_ETM_ISA_T32)
> +               insn_len = cs_etm__t32_instr_size(etmq, trace_chan_id, addr);
> +       /* Otherwise, A64 and A32 instruction size are always 32-bit. */
> +       else
> +               insn_len = 4;
> +
> +       return insn_len;
> +}
> +
>  static inline u64 cs_etm__first_executed_instr(struct cs_etm_packet *packet)
>  {
>         /* Returns 0 for the CS_ETM_DISCONTINUITY packet */
> @@ -942,19 +962,15 @@ static inline u64 cs_etm__instr_addr(struct cs_etm_queue *etmq,
>                                      const struct cs_etm_packet *packet,
>                                      u64 offset)
>  {
> -       if (packet->isa == CS_ETM_ISA_T32) {
> -               u64 addr = packet->start_addr;
> +       u64 addr = packet->start_addr;
>
> -               while (offset) {
> -                       addr += cs_etm__t32_instr_size(etmq,
> -                                                      trace_chan_id, addr);
> -                       offset--;
> -               }
> -               return addr;
> +       while (offset) {
> +               addr += cs_etm__instr_size(etmq, trace_chan_id,
> +                                          packet->isa, addr);
> +               offset--;
>         }
>
> -       /* Assume a 4 byte instruction size (A32/A64) */
> -       return packet->start_addr + offset * 4;
> +       return addr;
>  }
>
>  static void cs_etm__update_last_branch_rb(struct cs_etm_queue *etmq,
> @@ -1094,16 +1110,8 @@ static void cs_etm__copy_insn(struct cs_etm_queue *etmq,
>                 return;
>         }
>
> -       /*
> -        * T32 instruction size might be 32-bit or 16-bit, decide by calling
> -        * cs_etm__t32_instr_size().
> -        */
> -       if (packet->isa == CS_ETM_ISA_T32)
> -               sample->insn_len = cs_etm__t32_instr_size(etmq, trace_chan_id,
> -                                                         sample->ip);
> -       /* Otherwise, A64 and A32 instruction size are always 32-bit. */
> -       else
> -               sample->insn_len = 4;
> +       sample->insn_len = cs_etm__instr_size(etmq, trace_chan_id,
> +                                             packet->isa, sample->ip);
>
>         cs_etm__mem_access(etmq, trace_chan_id, sample->ip,
>                            sample->insn_len, (void *)sample->insn);
> --
> 2.17.1
>


-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK