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

From: Suzuki K Poulose
Date: Tue Jan 31 2023 - 06:49:25 EST


Hi Arnaldo

On 24/01/2023 11:36, Suzuki K Poulose wrote:
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 ?

Please could you confirm if you are able to queue the perf tool changes ? Or would you like me route it via coresight tree ?

Kind regards
Suzuki