linux-kernel - Re: [PATCH v7 00/15] coresight: Add new API to allocate trace source ID values

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Message-ID: <5b7df6df-0c2d-6953-0f50-e85745cb1f4b@arm.com>
Date:   Tue, 24 Jan 2023 11:36:10 +0000
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     mathieu.poirier@...aro.org, peterz@...radead.org, mingo@...hat.com,
        linux-perf-users@...r.kernel.org, leo.yan@...aro.org,
        quic_jinlmao@...cinc.com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Mike Leach <mike.leach@...aro.org>,
        James Clark <james.clark@....com>
Subject: Re: [PATCH v7 00/15] coresight: Add new API to allocate trace source
 ID values

Hi Arnaldo

Gentle ping.

On 19/01/2023 12:00, Suzuki K Poulose wrote:
> Hi Arnaldo,
> 
> On 16/01/2023 12:49, Mike Leach wrote:
>> The current method for allocating trace source ID values to sources is
>> to use a fixed algorithm for CPU based sources of (cpu_num * 2 + 0x10).
>> The STM is allocated ID 0x1.
>>
>> This fixed algorithm is used in both the CoreSight driver code, and by
>> perf when writing the trace metadata in the AUXTRACE_INFO record.
>>
>> The method needs replacing as currently:-
>> 1. It is inefficient in using available IDs.
>> 2. Does not scale to larger systems with many cores and the algorithm
>> has no limits so will generate invalid trace IDs for cpu number > 44.
>>
>> Additionally requirements to allocate additional system IDs on some
>> systems have been seen.
>>
>> This patch set  introduces an API that allows the allocation of trace IDs
>> in a dynamic manner.
>>
>> Architecturally reserved IDs are never allocated, and the system is
>> limited to allocating only valid IDs.
>>
>> Each of the current trace sources ETM3.x, ETM4.x and STM is updated to 
>> use
>> the new API.
>>
>> For the ETMx.x devices IDs are allocated on certain events
>> a) When using sysfs, an ID will be allocated on hardware enable, or a 
>> read of
>> sysfs TRCTRACEID register and freed when the sysfs reset is written.
>>
>> b) When using perf, ID is allocated on during setup AUX event, and 
>> freed on
>> event free. IDs are communicated using the AUX_OUTPUT_HW_ID packet.
>> The ID allocator is notified when perf sessions start and stop
>> so CPU based IDs are kept constant throughout any perf session.
>>
>>
>> Note: This patchset breaks some backward compatibility for perf record 
>> and
>> perf report.
>>
>> The version of the AUXTRACE_INFO has been updated to reflect the fact 
>> that
>> the trace source IDs are generated differently. This will
>> mean older versions of perf report cannot decode the newer file.
>>
>> Appies to coresight/next
>>

...

>> Mike Leach (15):
>>    coresight: trace-id: Add API to dynamically assign Trace ID values
>>    coresight: Remove obsolete Trace ID unniqueness checks
>>    coresight: perf: traceid: Add perf ID allocation and notifiers
>>    coresight: stm: Update STM driver to use Trace ID API
>>    coresight: etm4x: Update ETM4 driver to use Trace ID API
>>    coresight: etm3x: Update ETM3 driver to use Trace ID API
>>    coresight: etmX.X: stm: Remove trace_id() callback
>>    coresight: trace id: Remove legacy get trace ID function.
>>    perf: cs-etm: Move mapping of Trace ID and cpu into helper function
>>    perf: cs-etm: Update record event to use new Trace ID protocol
>>    kernel: events: Export perf_report_aux_output_id()
>>    perf: cs-etm: Handle PERF_RECORD_AUX_OUTPUT_HW_ID packet
>>    coresight: events: PERF_RECORD_AUX_OUTPUT_HW_ID used for Trace ID
>>    coresight: trace-id: Add debug & test macros to Trace ID allocation
>>    coresight: etm3x: docs: Alter sysfs documentation for trace id updates
> 
> I have pushed the kernel patches on this series to coresight tree next[0].
> 
> I will be sending them out to Greg for v6.3. Please could you queue the
> perf tool changes in the series ? i.e., Patches 9,10 and 12.
> 
> 
> [0] 
> https://git.kernel.org/pub/scm/linux/kernel/git/coresight/linux.git/log/?h=next
> 

Please could you pick up the perf tool changes above ?

Suzuki