trappy/ftrace: add support for boot clock timestamp

[derkling]

FTrace can be configured to report events timestamp using different clock sources which can be selected via the trace_clock sysfs attribute as described in: https://www.kernel.org/doc/Documentation/trace/ftrace.txt

The global clock source reports time in [s] with a [us] resolution. Other sources instead, like for example the boot clock, uses [ns]. Thus, in these last cases we do not have decimals in the timestamp.

Let's update the special fields regexp to match both [s] and [ns] formatted times. This also update the base test to add a set of trace events which are expressed in [ns] resolution.

Signed-off-by: Patrick Bellasi patrick.bellasi@arm.com

[derkling]

Maybe @joelagnel can be interested in having a look since I think he had a similar "issue" with some Android traces in the past.

[bjackman]

The documentation says "the timestamp in . format" so I wonder if this is a bug in a device kernel? If it's not going to be fixed in the kernel then yeah I guess we have to support it here.

[derkling]

@bjackman the only reference I can find related to the "." format is related to the specific description of the function tracer, I'm looking at this file: https://www.kernel.org/doc/Documentation/trace/ftrace.txt ... thus it could be very well a post-processing formatting.

Moreover, the description of the trace_clock parameter says that the boot clock comes from ktime_get_boot_fast_ns()... which name suggests it should return a ns based timestamp. There is also an explicit reference to possible required post-processing.

[derkling]

Update:

• detect [s].[us] format using an additional regexp capture group
• pre-process [ns] timestamps to convert them in [s].[decimals] format
• update test_base to properly check for timestamps which are always expressed in the [s].[decimals] foramt

[credp]

As I understand it the timestamp format in a trace depends upon the configured trace_clock - it's perfectly possible and valid to use the nanosecond boot clock.

[derkling]

Update:

• added a comment to explain the timestamp adjustments

[joelagnel]

LGTM... Let's get it merged ASAP 😁😁

[sinkap]

Merged.