Re: [PATCH v2 09/13] perf: cs-etm: Update record event to use new Trace ID protocol

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

On 09/08/2022 17:13, Mike Leach wrote:
> Hi James
> 
> On Wed, 20 Jul 2022 at 15:41, James Clark <james.clark@arm.com> wrote:
>>
>>
>>
>> On 04/07/2022 09:11, Mike Leach wrote:
>>> Trace IDs are now dynamically allocated.
>>>
>>> Previously used the static association algorithm that is no longer
>>> used. The 'cpu * 2 + seed' was outdated and broken for systems with high
>>> core counts (>46). as it did not scale and was broken for larger
>>> core counts.
>>>
>>> Trace ID is  as unknown in AUXINFO record, and the ID / CPU association
>>> will now be sent in PERF_RECORD_AUX_OUTPUT_HW_ID record.
>>>
>>> Remove legacy Trace ID allocation algorithm.
>>>
>>> Signed-off-by: Mike Leach <mike.leach@linaro.org>
>>> ---
>>>  include/linux/coresight-pmu.h       | 19 +++++++------------
>>>  tools/include/linux/coresight-pmu.h | 19 +++++++------------
>>
>> I usually see mentions that these header updates need to be separate commits
>> because they are merged through different trees.
>>
>>>  tools/perf/arch/arm/util/cs-etm.c   | 21 ++++++++++++---------
>>>  3 files changed, 26 insertions(+), 33 deletions(-)
>>>
>>> diff --git a/include/linux/coresight-pmu.h b/include/linux/coresight-pmu.h
>>> index 4ac5c081af93..9f7ee380266b 100644
>>> --- a/include/linux/coresight-pmu.h
>>> +++ b/include/linux/coresight-pmu.h
>>> @@ -8,7 +8,13 @@
>>>  #define _LINUX_CORESIGHT_PMU_H
>>>
>>>  #define CORESIGHT_ETM_PMU_NAME "cs_etm"
>>> -#define CORESIGHT_ETM_PMU_SEED  0x10
>>> +
>>> +/*
>>> + * Metadata now contains an unused trace ID - IDs are transmitted using a
>>> + * PERF_RECORD_AUX_OUTPUT_HW_ID record.
>>> + * Value architecturally defined as reserved in CoreSight.
>>> + */
>>> +#define CS_UNUSED_TRACE_ID 0x7F
>>>
>>>  /*
>>>   * Below are the definition of bit offsets for perf option, and works as
>>> @@ -32,15 +38,4 @@
>>>  #define ETM4_CFG_BIT_RETSTK  12
>>>  #define ETM4_CFG_BIT_VMID_OPT        15
>>>
>>> -static inline int coresight_get_trace_id(int cpu)
>>> -{
>>> -     /*
>>> -      * A trace ID of value 0 is invalid, so let's start at some
>>> -      * random value that fits in 7 bits and go from there.  Since
>>> -      * the common convention is to have data trace IDs be I(N) + 1,
>>> -      * set instruction trace IDs as a function of the CPU number.
>>> -      */
>>> -     return (CORESIGHT_ETM_PMU_SEED + (cpu * 2));
>>> -}
>>> -
>>>  #endif
>>> diff --git a/tools/include/linux/coresight-pmu.h b/tools/include/linux/coresight-pmu.h
>>> index 6c2fd6cc5a98..31d007fab3a6 100644
>>> --- a/tools/include/linux/coresight-pmu.h
>>> +++ b/tools/include/linux/coresight-pmu.h
>>> @@ -8,7 +8,13 @@
>>>  #define _LINUX_CORESIGHT_PMU_H
>>>
>>>  #define CORESIGHT_ETM_PMU_NAME "cs_etm"
>>> -#define CORESIGHT_ETM_PMU_SEED  0x10
>>> +
>>> +/*
>>> + * Metadata now contains an unused trace ID - IDs are transmitted using a
>>> + * PERF_RECORD_AUX_OUTPUT_HW_ID record.
>>> + * Value architecturally defined as reserved in CoreSight.
>>> + */
>>> +#define CS_UNUSED_TRACE_ID 0x7F
>>>
>>
>> minor nit: this isn't used in the kernel so only needs to be defined on the
>> tools side.
>>
> 
> Unfortunately if the two versions of coresight-pmu.h are different,
> the build process for perf throws out a warning. So they have to be
> identical.

I was thinking more along the lines of putting it in a header that is
only present on the perf side, rather than only having it in one version
of a shared header.

> 
> Thanks
> 
> Mike
> 
>>>  /*
>>>   * Below are the definition of bit offsets for perf option, and works as
>>> @@ -34,15 +40,4 @@
>>>  #define ETM4_CFG_BIT_RETSTK  12
>>>  #define ETM4_CFG_BIT_VMID_OPT        15
>>>
>>> -static inline int coresight_get_trace_id(int cpu)
>>> -{
>>> -     /*
>>> -      * A trace ID of value 0 is invalid, so let's start at some
>>> -      * random value that fits in 7 bits and go from there.  Since
>>> -      * the common convention is to have data trace IDs be I(N) + 1,
>>> -      * set instruction trace IDs as a function of the CPU number.
>>> -      */
>>> -     return (CORESIGHT_ETM_PMU_SEED + (cpu * 2));
>>> -}
>>> -
>>>  #endif
>>> diff --git a/tools/perf/arch/arm/util/cs-etm.c b/tools/perf/arch/arm/util/cs-etm.c
>>> index 1b54638d53b0..2d68e6a722ed 100644
>>> --- a/tools/perf/arch/arm/util/cs-etm.c
>>> +++ b/tools/perf/arch/arm/util/cs-etm.c
>>> @@ -421,13 +421,16 @@ static int cs_etm_recording_options(struct auxtrace_record *itr,
>>>       evlist__to_front(evlist, cs_etm_evsel);
>>>
>>>       /*
>>> -      * In the case of per-cpu mmaps, we need the CPU on the
>>> -      * AUX event.  We also need the contextID in order to be notified
>>> +      * get the CPU on the sample - need it to associate trace ID in the
>>> +      * AUX_OUTPUT_HW_ID event, and the AUX event for per-cpu mmaps.
>>> +      */
>>> +     evsel__set_sample_bit(cs_etm_evsel, CPU);
>>> +
>>> +     /*
>>> +      * Also the case of per-cpu mmaps, need the contextID in order to be notified
>>>        * when a context switch happened.
>>>        */
>>>       if (!perf_cpu_map__empty(cpus)) {
>>> -             evsel__set_sample_bit(cs_etm_evsel, CPU);
>>> -
>>>               err = cs_etm_set_option(itr, cs_etm_evsel,
>>>                                       BIT(ETM_OPT_CTXTID) | BIT(ETM_OPT_TS));
>>>               if (err)
>>> @@ -633,8 +636,9 @@ static void cs_etm_save_etmv4_header(__u64 data[], struct auxtrace_record *itr,
>>>
>>>       /* Get trace configuration register */
>>>       data[CS_ETMV4_TRCCONFIGR] = cs_etmv4_get_config(itr);
>>> -     /* Get traceID from the framework */
>>> -     data[CS_ETMV4_TRCTRACEIDR] = coresight_get_trace_id(cpu);
>>> +     /* traceID set to unused */
>>> +     data[CS_ETMV4_TRCTRACEIDR] = CS_UNUSED_TRACE_ID;
>>> +
>>>       /* Get read-only information from sysFS */
>>>       data[CS_ETMV4_TRCIDR0] = cs_etm_get_ro(cs_etm_pmu, cpu,
>>>                                              metadata_etmv4_ro[CS_ETMV4_TRCIDR0]);
>>> @@ -681,9 +685,8 @@ static void cs_etm_get_metadata(int cpu, u32 *offset,
>>>               magic = __perf_cs_etmv3_magic;
>>>               /* Get configuration register */
>>>               info->priv[*offset + CS_ETM_ETMCR] = cs_etm_get_config(itr);
>>> -             /* Get traceID from the framework */
>>> -             info->priv[*offset + CS_ETM_ETMTRACEIDR] =
>>> -                                             coresight_get_trace_id(cpu);
>>> +             /* traceID set to unused */
>>> +             info->priv[*offset + CS_ETM_ETMTRACEIDR] = CS_UNUSED_TRACE_ID;
>>>               /* Get read-only information from sysFS */
>>>               info->priv[*offset + CS_ETM_ETMCCER] =
>>>                       cs_etm_get_ro(cs_etm_pmu, cpu,
> 
> 
>