[PATCH V9 12/13] perf intel-pt: Add documentation for pause / resume

Adrian Hunter
2024-07-15T16:08:33Z

Document the use of aux-action config term and provide a simple example.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Ian Rogers <irogers@google.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
---

Changes in V5:
Added more examples

tools/perf/Documentation/perf-intel-pt.txt | 108 +++++++++++++++++++++
1 file changed, 108 insertions(+)

diff --git a/tools/perf/Documentation/perf-intel-pt.txt b/tools/perf/Documentation/perf-intel-pt.txt
index ad39bf20f862..cc0f37f0fa5a 100644
--- a/tools/perf/Documentation/perf-intel-pt.txt
+++ b/tools/perf/Documentation/perf-intel-pt.txt
@@ -555,6 +555,9 @@ Support for this feature is indicated by:
which contains "1" if the feature is supported and
"0" otherwise.

+*aux-action=start-paused*::
+Start tracing paused, refer to the section <<_pause_or_resume_tracing,Pause or Resume Tracing>>
+

config terms on other events
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -570,6 +573,9 @@ and PEBS-via-PT. In those cases, the other events can have config terms below:
Used to select PEBS-via-PT, refer to the
section <<_pebs_via_intel_pt,PEBS via Intel PT>>

+*aux-action*::
+ Used to pause or resume tracing, refer to the section
+ <<_pause_or_resume_tracing,Pause or Resume Tracing>>

AUX area sampling option
~~~~~~~~~~~~~~~~~~~~~~~~
@@ -1915,6 +1921,108 @@ For pipe mode, the order of events and timestamps can presumably
be messed up.

+Pause or Resume Tracing
+-----------------------
+
+With newer Kernels, it is possible to use other selected events to pause
+or resume Intel PT tracing. This is configured by using the "aux-action"
+config term:
+
+"aux-action=pause" is used with events that are to pause Intel PT tracing.
+
+"aux-action=resume" is used with events that are to resume Intel PT tracing.
+
+"aux-action=start-paused" is used with the Intel PT event to start in a
+paused state.
+
+For example, to trace only the uname system call (sys_newuname) when running the
+command line utility uname:
+
+ $ perf record --kcore -e intel_pt/aux-action=start-paused/k,syscalls:sys_enter_newuname/aux-action=resume/,syscalls:sys_exit_newuname/aux-action=pause/ uname
+ Linux
+ [ perf record: Woken up 1 times to write data ]
+ [ perf record: Captured and wrote 0.043 MB perf.data ]
+ $ perf script --call-trace
+ uname 30805 [000] 24001.058782799: name: 0x7ffc9c1865b0
+ uname 30805 [000] 24001.058784424: psb offs: 0
+ uname 30805 [000] 24001.058784424: cbr: 39 freq: 3904 MHz (139%)
+ uname 30805 [000] 24001.058784629: ([kernel.kallsyms]) debug_smp_processor_id
+ uname 30805 [000] 24001.058784629: ([kernel.kallsyms]) __x64_sys_newuname
+ uname 30805 [000] 24001.058784629: ([kernel.kallsyms]) down_read
+ uname 30805 [000] 24001.058784629: ([kernel.kallsyms]) __cond_resched
+ uname 30805 [000] 24001.058784629: ([kernel.kallsyms]) preempt_count_add
+ uname 30805 [000] 24001.058784629: ([kernel.kallsyms]) in_lock_functions
+ uname 30805 [000] 24001.058784629: ([kernel.kallsyms]) preempt_count_sub
+ uname 30805 [000] 24001.058784629: ([kernel.kallsyms]) up_read
+ uname 30805 [000] 24001.058784629: ([kernel.kallsyms]) preempt_count_add
+ uname 30805 [000] 24001.058784838: ([kernel.kallsyms]) in_lock_functions
+ uname 30805 [000] 24001.058784838: ([kernel.kallsyms]) preempt_count_sub
+ uname 30805 [000] 24001.058784838: ([kernel.kallsyms]) _copy_to_user
+ uname 30805 [000] 24001.058784838: ([kernel.kallsyms]) syscall_exit_to_user_mode
+ uname 30805 [000] 24001.058784838: ([kernel.kallsyms]) syscall_exit_work
+ uname 30805 [000] 24001.058784838: ([kernel.kallsyms]) perf_syscall_exit
+ uname 30805 [000] 24001.058784838: ([kernel.kallsyms]) debug_smp_processor_id
+ uname 30805 [000] 24001.058785046: ([kernel.kallsyms]) perf_trace_buf_alloc
+ uname 30805 [000] 24001.058785046: ([kernel.kallsyms]) perf_swevent_get_recursion_context
+ uname 30805 [000] 24001.058785046: ([kernel.kallsyms]) debug_smp_processor_id
+ uname 30805 [000] 24001.058785046: ([kernel.kallsyms]) debug_smp_processor_id
+ uname 30805 [000] 24001.058785046: ([kernel.kallsyms]) perf_tp_event
+ uname 30805 [000] 24001.058785046: ([kernel.kallsyms]) perf_trace_buf_update
+ uname 30805 [000] 24001.058785046: ([kernel.kallsyms]) tracing_gen_ctx_irq_test
+ uname 30805 [000] 24001.058785046: ([kernel.kallsyms]) perf_swevent_event
+ uname 30805 [000] 24001.058785046: ([kernel.kallsyms]) __perf_event_account_interrupt
+ uname 30805 [000] 24001.058785046: ([kernel.kallsyms]) __this_cpu_preempt_check
+ uname 30805 [000] 24001.058785046: ([kernel.kallsyms]) perf_event_output_forward
+ uname 30805 [000] 24001.058785046: ([kernel.kallsyms]) perf_event_aux_pause
+ uname 30805 [000] 24001.058785046: ([kernel.kallsyms]) ring_buffer_get
+ uname 30805 [000] 24001.058785046: ([kernel.kallsyms]) __rcu_read_lock
+ uname 30805 [000] 24001.058785046: ([kernel.kallsyms]) __rcu_read_unlock
+ uname 30805 [000] 24001.058785254: ([kernel.kallsyms]) pt_event_stop
+ uname 30805 [000] 24001.058785254: ([kernel.kallsyms]) debug_smp_processor_id
+ uname 30805 [000] 24001.058785254: ([kernel.kallsyms]) debug_smp_processor_id
+ uname 30805 [000] 24001.058785254: ([kernel.kallsyms]) native_write_msr
+ uname 30805 [000] 24001.058785463: ([kernel.kallsyms]) native_write_msr
+ uname 30805 [000] 24001.058785639: 0x0
+
+The example above uses tracepoints, but any kind of sampled event can be used.
+
+For example:
+
+ Tracing between arch_cpu_idle_enter() and arch_cpu_idle_exit() using breakpoint events:
+
+ $ sudo cat /proc/kallsyms | sort | grep ' arch_cpu_idle_enter\| arch_cpu_idle_exit'
+ ffffffffb605bf60 T arch_cpu_idle_enter
+ ffffffffb614d8a0 W arch_cpu_idle_exit
+ $ sudo perf record --kcore -a -e intel_pt/aux-action=start-paused/k -e mem:0xffffffffb605bf60:x/aux-action=resume/ -e mem:0xffffffffb614d8a0:x/aux-action=pause/ -- sleep 1
+ [ perf record: Woken up 1 times to write data ]
+ [ perf record: Captured and wrote 1.387 MB perf.data ]
+
+ Tracing __alloc_pages() using kprobes:
+
+ $ sudo perf probe --add '__alloc_pages order'
+ Added new event: probe:__alloc_pages (on __alloc_pages with order)
+ $ sudo perf probe --add __alloc_pages%return
+ Added new event: probe:__alloc_pages__return (on __alloc_pages%return)
+ $ sudo perf record --kcore -aR -e intel_pt/aux-action=start-paused/k -e probe:__alloc_pages/aux-action=resume/ -e probe:__alloc_pages__return/aux-action=pause/ -- sleep 1
+ [ perf record: Woken up 1 times to write data ]
+ [ perf record: Captured and wrote 1.490 MB perf.data ]
+
+ Tracing starting at main() using a uprobe event:
+
+ $ sudo perf probe -x /usr/bin/uname main
+ Added new event: probe_uname:main (on main in /usr/bin/uname)
+ $ sudo perf record -e intel_pt/-aux-action=start-paused/u -e probe_uname:main/aux-action=resume/ -- uname
+ Linux
+ [ perf record: Woken up 1 times to write data ]
+ [ perf record: Captured and wrote 0.031 MB perf.data ]
+
+ Tracing occasionally using cycles events with different periods:
+
+ $ perf record --kcore -a -m,64M -e intel_pt/aux-action=start-paused/k -e cycles/aux-action=pause,period=1000000/Pk -e cycles/aux-action=resume,period=10500000/Pk -- firefox
+ [ perf record: Woken up 19 times to write data ]
+ [ perf record: Captured and wrote 16.561 MB perf.data ]
+
+
EXAMPLE
-------

--
2.34.1