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collector/ftrace: Use top-level buffer instance

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Abandon the use of non-toplevel buffer instance (-B parameter), as they
are not worth the hassle. A number of frace features do not interact
well with them such as:
* bprint event emitted by trace_printk(), that always lands in the
  top-level buffer no matter what.
* synthetic events that can also only reasonably be emitted in the
  top-level buffer as of Linux 6.13
This commit is contained in:
Douglas Raillard 2025-03-17 14:21:47 +00:00 committed by Marc Bonnici
parent f02a0a38b0
commit f71b6a7d96
1 changed files with 30 additions and 11 deletions

41
devlib/collector/ftrace.py

@ -200,6 +200,19 @@ class FtraceCollector(CollectorBase):
self._selected_events = selected_events
@property
def _buffer_size(self):
top = self.top_buffer_size
nontop = self.buffer_size
if top is None and nontop is None:
return None
elif top is None:
return nontop
elif nontop is None:
return top
else:
return max(top, nontop)
@property
def event_string(self):
return _build_trace_events(self._selected_events)
@ -254,19 +267,25 @@ class FtraceCollector(CollectorBase):
except TargetStableError:
kprobe_events = None
self.target.execute('{} reset -B devlib'.format(self.target_binary),
self.target.execute('{} reset'.format(self.target_binary),
as_root=True, timeout=TIMEOUT)
# This code is currently not necessary as we are not using alternate
# instances (not using -B parameter). If we end up using it again, it
# may very well be that trace-cmd at that point takes care of that
# problem itself somehow, so this should be re-evaluated.
# trace-cmd start will not set the top-level buffer size if passed -B
# parameter, but unfortunately some events still end up there (e.g.
# print event). So we still need to set that size, otherwise the buffer
# might be too small and some event lost.
top_buffer_size = self.top_buffer_size if self.top_buffer_size else self.buffer_size
if top_buffer_size:
self.target.write_value(
self.target.path.join(self.tracing_path, 'buffer_size_kb'),
top_buffer_size, verify=False
)
# top_buffer_size = self.top_buffer_size or self.buffer_size
# if top_buffer_size:
# self.target.write_value(
# self.target.path.join(self.tracing_path, 'buffer_size_kb'),
# top_buffer_size, verify=False
# )
if self.functions:
self.target.write_value(self.function_profile_file, 0, verify=False)
@ -315,11 +334,11 @@ class FtraceCollector(CollectorBase):
with contextlib.suppress(TargetStableError):
self.target.write_value('/proc/sys/kernel/kptr_restrict', 0)
params = '-B devlib {buffer_size} {cmdlines_size} {clock} {events} {tracer} {functions}'.format(
params = '{buffer_size} {cmdlines_size} {clock} {events} {tracer} {functions}'.format(
events=self.event_string,
tracer=tracer_string,
functions=tracecmd_functions,
buffer_size='-b {}'.format(self.buffer_size) if self.buffer_size is not None else '',
buffer_size='-b {}'.format(self._buffer_size) if self._buffer_size is not None else '',
clock='-C {}'.format(self.trace_clock) if self.trace_clock else '',
cmdlines_size='--cmdlines-size {}'.format(self.saved_cmdlines_nr) if self.saved_cmdlines_nr is not None else '',
)
@ -381,7 +400,7 @@ class FtraceCollector(CollectorBase):
bg_cmd.communicate()
bg_cmd.__exit__(None, None, None)
elif mode == 'write-to-memory':
self.target.execute('{} stop -B devlib'.format(self.target_binary),
self.target.execute('{} stop'.format(self.target_binary),
timeout=TIMEOUT, as_root=True)
else:
raise ValueError(f'Unknown mode {mode}')
@ -404,7 +423,7 @@ class FtraceCollector(CollectorBase):
# Interrupting trace-cmd record will make it create the file
pass
elif mode == 'write-to-memory':
cmd = f'{self.target_binary} extract -B devlib -o {self.target_output_file} && {busybox} chmod 666 {self.target_output_file}'
cmd = f'{self.target_binary} extract -o {self.target_output_file} && {busybox} chmod 666 {self.target_output_file}'
self.target.execute(cmd, timeout=TIMEOUT, as_root=True)
else:
raise ValueError(f'Unknown mode {mode}')