Re: [PATCH 3/6] perf cs-etm: Save TRCDEVARCH register

[James Clark <james.clark@arm.com>]

On 21/07/2021 10:48, Mike Leach wrote:
> HI James,
> 
> On Wed, 21 Jul 2021 at 10:07, James Clark <james.clark@arm.com> wrote:
>>
>> Now that the metadata has a length field we can add extra registers
>> without breaking any previous versions of perf.
>>
>> Save the TRCDEVARCH register so that it can be used to configure the ETE
>> decoder in the next commit. If the sysfs file doesn't exist then 0 will
>> be saved which is an impossible register value and can also be used to
>> signify that the file couldn't be read.
>>
>> Signed-off-by: James Clark <james.clark@arm.com>
>> ---
>>  tools/perf/arch/arm/util/cs-etm.c | 13 ++++++++++++-
>>  tools/perf/util/cs-etm.c          |  1 +
>>  tools/perf/util/cs-etm.h          |  5 +++--
>>  3 files changed, 16 insertions(+), 3 deletions(-)
>>
>> diff --git a/tools/perf/arch/arm/util/cs-etm.c b/tools/perf/arch/arm/util/cs-etm.c
>> index 85168d87b2d7..65a863bdf5cc 100644
>> --- a/tools/perf/arch/arm/util/cs-etm.c
>> +++ b/tools/perf/arch/arm/util/cs-etm.c
>> @@ -53,6 +53,7 @@ static const char *metadata_etmv4_ro[CS_ETMV4_PRIV_MAX] = {
>>         [CS_ETMV4_TRCIDR2]              = "trcidr/trcidr2",
>>         [CS_ETMV4_TRCIDR8]              = "trcidr/trcidr8",
>>         [CS_ETMV4_TRCAUTHSTATUS]        = "mgmt/trcauthstatus",
>> +       [CS_ETE_TRCDEVARCH]             = "mgmt/trcdevarch"
>>  };
>>
>>  static bool cs_etm_is_etmv4(struct auxtrace_record *itr, int cpu);
>> @@ -73,7 +74,7 @@ static int cs_etm_set_context_id(struct auxtrace_record *itr,
>>         if (!cs_etm_is_etmv4(itr, cpu))
>>                 goto out;
>>
>> -       /* Get a handle on TRCIRD2 */
>> +       /* Get a handle on TRCIDR2 */
>>         snprintf(path, PATH_MAX, "cpu%d/%s",
>>                  cpu, metadata_etmv4_ro[CS_ETMV4_TRCIDR2]);
>>         err = perf_pmu__scan_file(cs_etm_pmu, path, "%x", &val);
>> @@ -643,6 +644,16 @@ static void cs_etm_get_metadata(int cpu, u32 *offset,
>>                         cs_etm_get_ro(cs_etm_pmu, cpu,
>>                                       metadata_etmv4_ro
>>                                       [CS_ETMV4_TRCAUTHSTATUS]);
>> +               /*
>> +                * ETE uses the same registers as ETMv4 plus TRCDEVARCH. It's also backwards
>> +                * compatible, so don't change the magic number otherwise that will reduce the
>> +                * number of versions of perf that can open it. Just append TRCDEVARCH to the end of
>> +                * the register block and allow newer versions of perf to make use. cs_etm_get_ro()
>> +                * returns 0 if it couldn't be read.
>> +                */
> 
> ETE is a superset of ETMv4, but an old perf that only knows ETMv4
> cannot be guaranteed to decode all ETE due to new packet types.
> Therefore do we want to allow old perfs to decode only some ETE,
> possibly with errors?
> 
> I think it would be better to add in a new magic number for the new
> decoder rather than have some grey overlap area were an "older" perf
> might work intermittently dependent on the packets generated in a
> particular trace run.

I did think about doing it this way and I'm also ok with adding a new
magic number. I will wait till Al's back to get his opinion before
making the change.

Thanks
James

> 
> Regards
> 
> Mike
> 
>> +               info->priv[*offset + CS_ETE_TRCDEVARCH] =
>> +                       cs_etm_get_ro(cs_etm_pmu, cpu,
>> +                                     metadata_etmv4_ro[CS_ETE_TRCDEVARCH]);
>>
>>                 /* How much space was used */
>>                 increment = CS_ETMV4_PRIV_MAX;
>> diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
>> index 62769a84a53f..68978f6707a8 100644
>> --- a/tools/perf/util/cs-etm.c
>> +++ b/tools/perf/util/cs-etm.c
>> @@ -2508,6 +2508,7 @@ static const char * const cs_etmv4_priv_fmts[] = {
>>         [CS_ETMV4_TRCIDR2]      = "     TRCIDR2                        %llx\n",
>>         [CS_ETMV4_TRCIDR8]      = "     TRCIDR8                        %llx\n",
>>         [CS_ETMV4_TRCAUTHSTATUS] = "    TRCAUTHSTATUS                  %llx\n",
>> +       [CS_ETE_TRCDEVARCH]     = "     TRCDEVARCH                     %llx\n"
>>  };
>>
>>  static const char * const param_unk_fmt =
>> diff --git a/tools/perf/util/cs-etm.h b/tools/perf/util/cs-etm.h
>> index d65c7b19407d..52d82dce9d59 100644
>> --- a/tools/perf/util/cs-etm.h
>> +++ b/tools/perf/util/cs-etm.h
>> @@ -59,7 +59,7 @@ enum {
>>  /* define fixed version 0 length - allow new format reader to read old files. */
>>  #define CS_ETM_NR_TRC_PARAMS_V0 (CS_ETM_ETMIDR - CS_ETM_ETMCR + 1)
>>
>> -/* ETMv4 metadata */
>> +/* ETMv4 + ETE metadata */
>>  enum {
>>         /* Dynamic, configurable parameters */
>>         CS_ETMV4_TRCCONFIGR = CS_ETM_COMMON_BLK_MAX_V1,
>> @@ -70,7 +70,8 @@ enum {
>>         CS_ETMV4_TRCIDR2,
>>         CS_ETMV4_TRCIDR8,
>>         CS_ETMV4_TRCAUTHSTATUS,
>> -       CS_ETMV4_PRIV_MAX,
>> +       CS_ETE_TRCDEVARCH,
>> +       CS_ETMV4_PRIV_MAX
>>  };
>>
>>  /* define fixed version 0 length - allow new format reader to read old files. */
>> --
>> 2.28.0
>>
> 
>