Merge tag 'trace-v5.14' of git://git.kernel.org/pub/scm/linux/kernel/…

…git/rostedt/linux-trace

Pull tracing updates from Steven Rostedt:

 - Added option for per CPU threads to the hwlat tracer

 - Have hwlat tracer handle hotplug CPUs

 - New tracer: osnoise, that detects latency caused by interrupts,
   softirqs and scheduling of other tasks.

 - Added timerlat tracer that creates a thread and measures in detail
   what sources of latency it has for wake ups.

 - Removed the "success" field of the sched_wakeup trace event. This has
   been hardcoded as "1" since 2015, no tooling should be looking at it
   now. If one exists, we can revert this commit, fix that tool and try
   to remove it again in the future.

 - tgid mapping fixed to handle more than PID_MAX_DEFAULT pids/tgids.

 - New boot command line option "tp_printk_stop", as tp_printk causes
   trace events to write to console. When user space starts, this can
   easily live lock the system. Having a boot option to stop just after
   boot up is useful to prevent that from happening.

 - Have ftrace_dump_on_oops boot command line option take numbers that
   match the numbers shown in /proc/sys/kernel/ftrace_dump_on_oops.

 - Bootconfig clean ups, fixes and enhancements.

 - New ktest script that tests bootconfig options.

 - Add tracepoint_probe_register_may_exist() to register a tracepoint
   without triggering a WARN*() if it already exists. BPF has a path
   from user space that can do this. All other paths are considered a
   bug.

 - Small clean ups and fixes

* tag 'trace-v5.14' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace: (49 commits)
  tracing: Resize tgid_map to pid_max, not PID_MAX_DEFAULT
  tracing: Simplify & fix saved_tgids logic
  treewide: Add missing semicolons to __assign_str uses
  tracing: Change variable type as bool for clean-up
  trace/timerlat: Fix indentation on timerlat_main()
  trace/osnoise: Make 'noise' variable s64 in run_osnoise()
  tracepoint: Add tracepoint_probe_register_may_exist() for BPF tracing
  tracing: Fix spelling in osnoise tracer "interferences" -> "interference"
  Documentation: Fix a typo on trace/osnoise-tracer
  trace/osnoise: Fix return value on osnoise_init_hotplug_support
  trace/osnoise: Make interval u64 on osnoise_main
  trace/osnoise: Fix 'no previous prototype' warnings
  tracing: Have osnoise_main() add a quiescent state for task rcu
  seq_buf: Make trace_seq_putmem_hex() support data longer than 8
  seq_buf: Fix overflow in seq_buf_putmem_hex()
  trace/osnoise: Support hotplug operations
  trace/hwlat: Support hotplug operations
  trace/hwlat: Protect kdata->kthread with get/put_online_cpus
  trace: Add timerlat tracer
  trace: Add osnoise tracer
  ...

Documentation/admin-guide/bootconfig.rst

@@ -89,13 +89,35 @@ you can use ``+=`` operator. For example::
 
 In this case, the key ``foo`` has ``bar``, ``baz`` and ``qux``.
 
-However, a sub-key and a value can not co-exist under a parent key.
-For example, following config is NOT allowed.::
+Moreover, sub-keys and a value can coexist under a parent key.
+For example, following config is allowed.::
 
  foo = value1
- foo.bar = value2 # !ERROR! subkey "bar" and value "value1" can NOT co-exist
- foo.bar := value2 # !ERROR! even with the override operator, this is NOT allowed.
+ foo.bar = value2
+ foo := value3 # This will update foo's value.
+
+Note, since there is no syntax to put a raw value directly under a
+structured key, you have to define it outside of the brace. For example::
+
+ foo {
+     bar = value1
+     bar {
+         baz = value2
+         qux = value3
+     }
+ }
+
+Also, the order of the value node under a key is fixed. If there
+are a value and subkeys, the value is always the first child node
+of the key. Thus if user specifies subkeys first, e.g.::
+
+ foo.bar = value1
+ foo = value2
+
+In the program (and /proc/bootconfig), it will be shown as below::
 
+ foo = value2
+ foo.bar = value1
 
 Comments
 --------

Documentation/admin-guide/kernel-parameters.txt

@@ -5672,12 +5672,25 @@
 			Note, echoing 1 into this file without the
 			tracepoint_printk kernel cmdline option has no effect.
 
+			The tp_printk_stop_on_boot (see below) can also be used
+			to stop the printing of events to console at
+			late_initcall_sync.
+
 			** CAUTION **
 
 			Having tracepoints sent to printk() and activating high
 			frequency tracepoints such as irq or sched, can cause
 			the system to live lock.
 
+	tp_printk_stop_on_boot[FTRACE]
+			When tp_printk (above) is set, it can cause a lot of noise
+			on the console. It may be useful to only include the
+			printing of events during boot up, as user space may
+			make the system inoperable.
+
+			This command line option will stop the printing of events
+			to console at the late_initcall_sync() time frame.
+
 	traceoff_on_warning
 			[FTRACE] enable this option to disable tracing when a
 			warning is hit. This turns off "tracing_on". Tracing can

Documentation/trace/boottime-trace.rst

@@ -99,6 +99,12 @@ These options are setting per-event options.
 ftrace.[instance.INSTANCE.]event.GROUP.EVENT.enable
    Enable GROUP:EVENT tracing.
 
+ftrace.[instance.INSTANCE.]event.GROUP.enable
+   Enable all event tracing within GROUP.
+
+ftrace.[instance.INSTANCE.]event.enable
+   Enable all event tracing.
+
 ftrace.[instance.INSTANCE.]event.GROUP.EVENT.filter = FILTER
    Set FILTER rule to the GROUP:EVENT.
 

Documentation/trace/hwlat_detector.rst

@@ -76,8 +76,13 @@ in /sys/kernel/tracing:
  - tracing_cpumask	- the CPUs to move the hwlat thread across
  - hwlat_detector/width	- specified amount of time to spin within window (usecs)
  - hwlat_detector/window	- amount of time between (width) runs (usecs)
+ - hwlat_detector/mode	- the thread mode
 
-The hwlat detector's kernel thread will migrate across each CPU specified in
-tracing_cpumask between each window. To limit the migration, either modify
-tracing_cpumask, or modify the hwlat kernel thread (named [hwlatd]) CPU
-affinity directly, and the migration will stop.
+By default, one hwlat detector's kernel thread will migrate across each CPU
+specified in cpumask at the beginning of a new window, in a round-robin
+fashion. This behavior can be changed by changing the thread mode,
+the available options are:
+
+ - none:        do not force migration
+ - round-robin: migrate across each CPU specified in cpumask [default]
+ - per-cpu:     create one thread for each cpu in tracing_cpumask

Documentation/trace/index.rst

@@ -23,6 +23,8 @@ Linux Tracing Technologies
    histogram-design
    boottime-trace
    hwlat_detector
+   osnoise-tracer
+   timerlat-tracer
    intel_th
    ring-buffer-design
    stm

Documentation/trace/osnoise-tracer.rst

@@ -0,0 +1,152 @@
+==============
+OSNOISE Tracer
+==============
+
+In the context of high-performance computing (HPC), the Operating System
+Noise (*osnoise*) refers to the interference experienced by an application
+due to activities inside the operating system. In the context of Linux,
+NMIs, IRQs, SoftIRQs, and any other system thread can cause noise to the
+system. Moreover, hardware-related jobs can also cause noise, for example,
+via SMIs.
+
+hwlat_detector is one of the tools used to identify the most complex
+source of noise: *hardware noise*.
+
+In a nutshell, the hwlat_detector creates a thread that runs
+periodically for a given period. At the beginning of a period, the thread
+disables interrupt and starts sampling. While running, the hwlatd
+thread reads the time in a loop. As interrupts are disabled, threads,
+IRQs, and SoftIRQs cannot interfere with the hwlatd thread. Hence, the
+cause of any gap between two different reads of the time roots either on
+NMI or in the hardware itself. At the end of the period, hwlatd enables
+interrupts and reports the max observed gap between the reads. It also
+prints a NMI occurrence counter. If the output does not report NMI
+executions, the user can conclude that the hardware is the culprit for
+the latency. The hwlat detects the NMI execution by observing
+the entry and exit of a NMI.
+
+The osnoise tracer leverages the hwlat_detector by running a
+similar loop with preemption, SoftIRQs and IRQs enabled, thus allowing
+all the sources of *osnoise* during its execution. Using the same approach
+of hwlat, osnoise takes note of the entry and exit point of any
+source of interferences, increasing a per-cpu interference counter. The
+osnoise tracer also saves an interference counter for each source of
+interference. The interference counter for NMI, IRQs, SoftIRQs, and
+threads is increased anytime the tool observes these interferences' entry
+events. When a noise happens without any interference from the operating
+system level, the hardware noise counter increases, pointing to a
+hardware-related noise. In this way, osnoise can account for any
+source of interference. At the end of the period, the osnoise tracer
+prints the sum of all noise, the max single noise, the percentage of CPU
+available for the thread, and the counters for the noise sources.
+
+Usage
+-----
+
+Write the ASCII text "osnoise" into the current_tracer file of the
+tracing system (generally mounted at /sys/kernel/tracing).
+
+For example::
+
+        [root@f32 ~]# cd /sys/kernel/tracing/
+        [root@f32 tracing]# echo osnoise > current_tracer
+
+It is possible to follow the trace by reading the trace trace file::
+
+        [root@f32 tracing]# cat trace
+        # tracer: osnoise
+        #
+        #                                _-----=> irqs-off
+        #                               / _----=> need-resched
+        #                              | / _---=> hardirq/softirq
+        #                              || / _--=> preempt-depth                            MAX
+        #                              || /                                             SINGLE     Interference counters:
+        #                              ||||               RUNTIME      NOISE   % OF CPU  NOISE    +-----------------------------+
+        #           TASK-PID      CPU# ||||   TIMESTAMP    IN US       IN US  AVAILABLE  IN US     HW    NMI    IRQ   SIRQ THREAD
+        #              | |         |   ||||      |           |             |    |            |      |      |      |      |      |
+                   <...>-859     [000] ....    81.637220: 1000000        190  99.98100       9     18      0   1007     18      1
+                   <...>-860     [001] ....    81.638154: 1000000        656  99.93440      74     23      0   1006     16      3
+                   <...>-861     [002] ....    81.638193: 1000000       5675  99.43250     202      6      0   1013     25     21
+                   <...>-862     [003] ....    81.638242: 1000000        125  99.98750      45      1      0   1011     23      0
+                   <...>-863     [004] ....    81.638260: 1000000       1721  99.82790     168      7      0   1002     49     41
+                   <...>-864     [005] ....    81.638286: 1000000        263  99.97370      57      6      0   1006     26      2
+                   <...>-865     [006] ....    81.638302: 1000000        109  99.98910      21      3      0   1006     18      1
+                   <...>-866     [007] ....    81.638326: 1000000       7816  99.21840     107      8      0   1016     39     19
+
+In addition to the regular trace fields (from TASK-PID to TIMESTAMP), the
+tracer prints a message at the end of each period for each CPU that is
+running an osnoise/ thread. The osnoise specific fields report:
+
+ - The RUNTIME IN US reports the amount of time in microseconds that
+   the osnoise thread kept looping reading the time.
+ - The NOISE IN US reports the sum of noise in microseconds observed
+   by the osnoise tracer during the associated runtime.
+ - The % OF CPU AVAILABLE reports the percentage of CPU available for
+   the osnoise thread during the runtime window.
+ - The MAX SINGLE NOISE IN US reports the maximum single noise observed
+   during the runtime window.
+ - The Interference counters display how many each of the respective
+   interference happened during the runtime window.
+
+Note that the example above shows a high number of HW noise samples.
+The reason being is that this sample was taken on a virtual machine,
+and the host interference is detected as a hardware interference.
+
+Tracer options
+---------------------
+
+The tracer has a set of options inside the osnoise directory, they are:
+
+ - osnoise/cpus: CPUs at which a osnoise thread will execute.
+ - osnoise/period_us: the period of the osnoise thread.
+ - osnoise/runtime_us: how long an osnoise thread will look for noise.
+ - osnoise/stop_tracing_us: stop the system tracing if a single noise
+   higher than the configured value happens. Writing 0 disables this
+   option.
+ - osnoise/stop_tracing_total_us: stop the system tracing if total noise
+   higher than the configured value happens. Writing 0 disables this
+   option.
+ - tracing_threshold: the minimum delta between two time() reads to be
+   considered as noise, in us. When set to 0, the default value will
+   will be used, which is currently 5 us.
+
+Additional Tracing
+------------------
+
+In addition to the tracer, a set of tracepoints were added to
+facilitate the identification of the osnoise source.
+
+ - osnoise:sample_threshold: printed anytime a noise is higher than
+   the configurable tolerance_ns.
+ - osnoise:nmi_noise: noise from NMI, including the duration.
+ - osnoise:irq_noise: noise from an IRQ, including the duration.
+ - osnoise:softirq_noise: noise from a SoftIRQ, including the
+   duration.
+ - osnoise:thread_noise: noise from a thread, including the duration.
+
+Note that all the values are *net values*. For example, if while osnoise
+is running, another thread preempts the osnoise thread, it will start a
+thread_noise duration at the start. Then, an IRQ takes place, preempting
+the thread_noise, starting a irq_noise. When the IRQ ends its execution,
+it will compute its duration, and this duration will be subtracted from
+the thread_noise, in such a way as to avoid the double accounting of the
+IRQ execution. This logic is valid for all sources of noise.
+
+Here is one example of the usage of these tracepoints::
+
+       osnoise/8-961     [008] d.h.  5789.857532: irq_noise: local_timer:236 start 5789.857529929 duration 1845 ns
+       osnoise/8-961     [008] dNh.  5789.858408: irq_noise: local_timer:236 start 5789.858404871 duration 2848 ns
+     migration/8-54      [008] d...  5789.858413: thread_noise: migration/8:54 start 5789.858409300 duration 3068 ns
+       osnoise/8-961     [008] ....  5789.858413: sample_threshold: start 5789.858404555 duration 8812 ns interferences 2
+
+In this example, a noise sample of 8 microseconds was reported in the last
+line, pointing to two interferences. Looking backward in the trace, the
+two previous entries were about the migration thread running after a
+timer IRQ execution. The first event is not part of the noise because
+it took place one millisecond before.
+
+It is worth noticing that the sum of the duration reported in the
+tracepoints is smaller than eight us reported in the sample_threshold.
+The reason roots in the overhead of the entry and exit code that happens
+before and after any interference execution. This justifies the dual
+approach: measuring thread and tracing.