diff options
34 files changed, 5686 insertions, 1922 deletions
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 8ccbf27aead4..5abc09a93bc2 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -320,6 +320,13 @@ bytes respectively. Such letter suffixes can also be entirely omitted. on: enable for both 32- and 64-bit processes off: disable for both 32- and 64-bit processes + alloc_snapshot [FTRACE] + Allocate the ftrace snapshot buffer on boot up when the + main buffer is allocated. This is handy if debugging + and you need to use tracing_snapshot() on boot up, and + do not want to use tracing_snapshot_alloc() as it needs + to be done where GFP_KERNEL allocations are allowed. + amd_iommu= [HW,X86-64] Pass parameters to the AMD IOMMU driver in the system. Possible values are: diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt index a372304aef10..bfe8c29b1f1d 100644 --- a/Documentation/trace/ftrace.txt +++ b/Documentation/trace/ftrace.txt @@ -8,6 +8,7 @@ Copyright 2008 Red Hat Inc. Reviewers: Elias Oltmanns, Randy Dunlap, Andrew Morton, John Kacur, and David Teigland. Written for: 2.6.28-rc2 +Updated for: 3.10 Introduction ------------ @@ -17,13 +18,16 @@ designers of systems to find what is going on inside the kernel. It can be used for debugging or analyzing latencies and performance issues that take place outside of user-space. -Although ftrace is the function tracer, it also includes an -infrastructure that allows for other types of tracing. Some of -the tracers that are currently in ftrace include a tracer to -trace context switches, the time it takes for a high priority -task to run after it was woken up, the time interrupts are -disabled, and more (ftrace allows for tracer plugins, which -means that the list of tracers can always grow). +Although ftrace is typically considered the function tracer, it +is really a frame work of several assorted tracing utilities. +There's latency tracing to examine what occurs between interrupts +disabled and enabled, as well as for preemption and from a time +a task is woken to the task is actually scheduled in. + +One of the most common uses of ftrace is the event tracing. +Through out the kernel is hundreds of static event points that +can be enabled via the debugfs file system to see what is +going on in certain parts of the kernel. Implementation Details @@ -61,7 +65,7 @@ the extended "/sys/kernel/debug/tracing" path name. That's it! (assuming that you have ftrace configured into your kernel) -After mounting the debugfs, you can see a directory called +After mounting debugfs, you can see a directory called "tracing". This directory contains the control and output files of ftrace. Here is a list of some of the key files: @@ -84,7 +88,9 @@ of ftrace. Here is a list of some of the key files: This sets or displays whether writing to the trace ring buffer is enabled. Echo 0 into this file to disable - the tracer or 1 to enable it. + the tracer or 1 to enable it. Note, this only disables + writing to the ring buffer, the tracing overhead may + still be occurring. trace: @@ -109,7 +115,15 @@ of ftrace. Here is a list of some of the key files: This file lets the user control the amount of data that is displayed in one of the above output - files. + files. Options also exist to modify how a tracer + or events work (stack traces, timestamps, etc). + + options: + + This is a directory that has a file for every available + trace option (also in trace_options). Options may also be set + or cleared by writing a "1" or "0" respectively into the + corresponding file with the option name. tracing_max_latency: @@ -121,10 +135,17 @@ of ftrace. Here is a list of some of the key files: latency is greater than the value in this file. (in microseconds) + tracing_thresh: + + Some latency tracers will record a trace whenever the + latency is greater than the number in this file. + Only active when the file contains a number greater than 0. + (in microseconds) + buffer_size_kb: This sets or displays the number of kilobytes each CPU - buffer can hold. The tracer buffers are the same size + buffer holds. By default, the trace buffers are the same size for each CPU. The displayed number is the size of the CPU buffer and not total size of all buffers. The trace buffers are allocated in pages (blocks of memory @@ -133,16 +154,30 @@ of ftrace. Here is a list of some of the key files: than requested, the rest of the page will be used, making the actual allocation bigger than requested. ( Note, the size may not be a multiple of the page size - due to buffer management overhead. ) + due to buffer management meta-data. ) - This can only be updated when the current_tracer - is set to "nop". + buffer_total_size_kb: + + This displays the total combined size of all the trace buffers. + + free_buffer: + + If a process is performing the tracing, and the ring buffer + should be shrunk "freed" when the process is finished, even + if it were to be killed by a signal, this file can be used + for that purpose. On close of this file, the ring buffer will + be resized to its minimum size. Having a process that is tracing + also open this file, when the process exits its file descriptor + for this file will be closed, and in doing so, the ring buffer + will be "freed". + + It may also stop tracing if disable_on_free option is set. tracing_cpumask: This is a mask that lets the user only trace - on specified CPUS. The format is a hex string - representing the CPUS. + on specified CPUs. The format is a hex string + representing the CPUs. set_ftrace_filter: @@ -183,6 +218,261 @@ of ftrace. Here is a list of some of the key files: "set_ftrace_notrace". (See the section "dynamic ftrace" below for more details.) + enabled_functions: + + This file is more for debugging ftrace, but can also be useful + in seeing if any function has a callback attached to it. + Not only does the trace infrastructure use ftrace function + trace utility, but other subsystems might too. This file + displays all functions that have a callback attached to them + as well as the number of callbacks that have been attached. + Note, a callback may also call multiple functions which will + not be listed in this count. + + If the callback registered to be traced by a function with + the "save regs" attribute (thus even more overhead), a 'R' + will be displayed on the same line as the function that + is returning registers. + + function_profile_enabled: + + When set it will enable all functions with either the function + tracer, or if enabled, the function graph tracer. It will + keep a histogram of the number of functions that were called + and if run with the function graph tracer, it will also keep + track of the time spent in those functions. The histogram + content can be displayed in the files: + + trace_stats/function<cpu> ( function0, function1, etc). + + trace_stats: + + A directory that holds different tracing stats. + + kprobe_events: + + Enable dynamic trace points. See kprobetrace.txt. + + kprobe_profile: + + Dynamic trace points stats. See kprobetrace.txt. + + max_graph_depth: + + Used with the function graph tracer. This is the max depth + it will trace into a function. Setting this to a value of + one will show only the first kernel function that is called + from user space. + + printk_formats: + + This is for tools that read the raw format files. If an event in + the ring buffer references a string (currently only trace_printk() + does this), only a pointer to the string is recorded into the buffer + and not the string itself. This prevents tools from knowing what + that string was. This file displays the string and address for + the string allowing tools to map the pointers to what the + strings were. + + saved_cmdlines: + + Only the pid of the task is recorded in a trace event unless + the event specifically saves the task comm as well. Ftrace + makes a cache of pid mappings to comms to try to display + comms for events. If a pid for a comm is not listed, then + "<...>" is displayed in the output. + + snapshot: + + This displays the "snapshot" buffer and also lets the user + take a snapshot of the current running trace. + See the "Snapshot" section below for more details. + + stack_max_size: + + When the stack tracer is activated, this will display the + maximum stack size it has encountered. + See the "Stack Trace" section below. + + stack_trace: + + This displays the stack back trace of the largest stack + that was encountered when the stack tracer is activated. + See the "Stack Trace" section below. + + stack_trace_filter: + + This is similar to "set_ftrace_filter" but it limits what + functions the stack tracer will check. + + trace_clock: + + Whenever an event is recorded into the ring buffer, a + "timestamp" is added. This stamp comes from a specified + clock. By default, ftrace uses the "local" clock. This + clock is very fast and strictly per cpu, but on some + systems it may not be monotonic with respect to other + CPUs. In other words, the local clocks may not be in sync + with local clocks on other CPUs. + + Usual clocks for tracing: + + # cat trace_clock + [local] global counter x86-tsc + + local: Default clock, but may not be in sync across CPUs + + global: This clock is in sync with all CPUs but may + be a bit slower than the local clock. + + counter: This is not a clock at all, but literally an atomic + counter. It counts up one by one, but is in sync + with all CPUs. This is useful when you need to + know exactly the order events occurred with respect to + each other on different CPUs. + + uptime: This uses the jiffies counter and the time stamp + is relative to the time since boot up. + + perf: This makes ftrace use the same clock that perf uses. + Eventually perf will be able to read ftrace buffers + and this will help out in interleaving the data. + + x86-tsc: Architectures may define their own clocks. For + example, x86 uses its own TSC cycle clock here. + + To set a clock, simply echo the clock name into this file. + + echo global > trace_clock + + trace_marker: + + This is a very useful file for synchronizing user space + with events happening in the kernel. Writing strings into + this file will be written into the ftrace buffer. + + It is useful in applications to open this file at the start + of the application and just reference the file descriptor + for the file. + + void trace_write(const char *fmt, ...) + { + va_list ap; + char buf[256]; + int n; + + if (trace_fd < 0) + return; + + va_start(ap, fmt); + n = vsnprintf(buf, 256, fmt, ap); + va_end(ap); + + write(trace_fd, buf, n); + } + + start: + + trace_fd = open("trace_marker", WR_ONLY); + + uprobe_events: + + Add dynamic tracepoints in programs. + See uprobetracer.txt + + uprobe_profile: + + Uprobe statistics. See uprobetrace.txt + + instances: + + This is a way to make multiple trace buffers where different + events can be recorded in different buffers. + See "Instances" section below. + + events: + + This is the trace event directory. It holds event tracepoints + (also known as static tracepoints) that have been compiled + into the kernel. It shows what event tracepoints exist + and how they are grouped by system. There are "enable" + files at various levels that can enable the tracepoints + when a "1" is written to them. + + See events.txt for more information. + + per_cpu: + + This is a directory that contains the trace per_cpu information. + + per_cpu/cpu0/buffer_size_kb: + + The ftrace buffer is defined per_cpu. That is, there's a separate + buffer for each CPU to allow writes to be done atomically, + and free from cache bouncing. These buffers may have different + size buffers. This file is similar to the buffer_size_kb + file, but it only displays or sets the buffer size for the + specific CPU. (here cpu0). + + per_cpu/cpu0/trace: + + This is similar to the "trace" file, but it will only display + the data specific for the CPU. If written to, it only clears + the specific CPU buffer. + + per_cpu/cpu0/trace_pipe + + This is similar to the "trace_pipe" file, and is a consuming + read, but it will only display (and consume) the data specific + for the CPU. + + per_cpu/cpu0/trace_pipe_raw + + For tools that can parse the ftrace ring buffer binary format, + the trace_pipe_raw file can be used to extract the data + from the ring buffer directly. With the use of the splice() + system call, the buffer data can be quickly transferred to + a file or to the network where a server is collecting the + data. + + Like trace_pipe, this is a consuming reader, where multiple + reads will always produce different data. + + per_cpu/cpu0/snapshot: + + This is similar to the main "snapshot" file, but will only + snapshot the current CPU (if supported). It only displays + the content of the snapshot for a given CPU, and if + written to, only clears this CPU buffer. + + per_cpu/cpu0/snapshot_raw: + + Similar to the trace_pipe_raw, but will read the binary format + from the snapshot buffer for the given CPU. + + per_cpu/cpu0/stats: + + This displays certain stats about the ring buffer: + + entries: The number of events that are still in the buffer. + + overrun: The number of lost events due to overwriting when + the buffer was full. + + commit overrun: Should always be zero. + This gets set if so many events happened within a nested + event (ring buffer is re-entrant), that it fills the + buffer and starts dropping events. + + bytes: Bytes actually read (not overwritten). + + oldest event ts: The oldest timestamp in the buffer + + now ts: The current timestamp + + dropped events: Events lost due to overwrite option being off. + + read events: The number of events read. The Tracers ----------- @@ -234,11 +524,6 @@ Here is the list of current tracers that may be configured. RT tasks (as the current "wakeup" does). This is useful for those interested in wake up timings of RT tasks. - "hw-branch-tracer" - - Uses the BTS CPU feature on x86 CPUs to traces all - branches executed. - "nop" This is the "trace nothing" tracer. To remove all @@ -261,70 +546,100 @@ Here is an example of the output format of the file "trace" -------- # tracer: function # -# TASK-PID CPU# TIMESTAMP FUNCTION -# | | | | | - bash-4251 [01] 10152.583854: path_put <-path_walk - bash-4251 [01] 10152.583855: dput <-path_put - bash-4251 [01] 10152.583855: _atomic_dec_and_lock <-dput +# entries-in-buffer/entries-written: 140080/250280 #P:4 +# +# _-----=> irqs-off +# / _----=> need-resched +# | / _---=> hardirq/softirq +# || / _--=> preempt-depth +# ||| / delay +# TASK-PID CPU# |||| TIMESTAMP FUNCTION +# | | | |||| | | + bash-1977 [000] .... 17284.993652: sys_close <-system_call_fastpath + bash-1977 [000] .... 17284.993653: __close_fd <-sys_close + bash-1977 [000] .... 17284.993653: _raw_spin_lock <-__close_fd + sshd-1974 [003] .... 17284.993653: __srcu_read_unlock <-fsnotify + bash-1977 [000] .... 17284.993654: add_preempt_count <-_raw_spin_lock + bash-1977 [000] ...1 17284.993655: _raw_spin_unlock <-__close_fd + bash-1977 [000] ...1 17284.993656: sub_preempt_count <-_raw_spin_unlock + bash-1977 [000] .... 17284.993657: filp_close <-__close_fd + bash-1977 [000] .... 17284.993657: dnotify_flush <-filp_close + sshd-1974 [003] .... 17284.993658: sys_select <-system_call_fastpath -------- A header is printed with the tracer name that is represented by -the trace. In this case the tracer is "function". Then a header -showing the format. Task name "bash", the task PID "4251", the -CPU that it was running on "01", the timestamp in <secs>.<usecs> -format, the function name that was traced "path_put" and the -parent function that called this function "path_walk". The -timestamp is the time at which the function was entered. +the trace. In this case the tracer is "function". Then it shows the +number of events in the buffer as well as the total number of entries +that were written. The difference is the number of entries that were +lost due to the buffer filling up (250280 - 140080 = 110200 events +lost). + +The header explains the content of the events. Task name "bash", the task +PID "1977", the CPU that it was running on "000", the latency format +(explained below), the timestamp in <secs>.<usecs> format, the +function name that was traced "sys_close" and the parent function that +called this function "system_call_fastpath". The timestamp is the time +at which the function was entered. Latency trace format -------------------- -When the latency-format option is enabled, the trace file gives -somewhat more information to see why a latency happened. -Here is a typical trace. +When the latency-format option is enabled or when one of the latency +tracers is set, the trace file gives somewhat more information to see +why a latency happened. Here is a typical trace. # tracer: irqsoff # -irqsoff latency trace v1.1.5 on 2.6.26-rc8 --------------------------------------------------------------------- - latency: 97 us, #3/3, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:2) - ----------------- - | task: swapper-0 (uid:0 nice:0 policy:0 rt_prio:0) - ----------------- - => started at: apic_timer_interrupt - => ended at: do_softirq - -# _------=> CPU# -# / _-----=> irqs-off -# | / _----=> need-resched -# || / _---=> hardirq/softirq -# ||| / _--=> preempt-depth -# |||| / -# ||||| delay -# cmd pid ||||| time | caller -# \ / ||||| \ | / - <idle>-0 0d..1 0us+: trace_hardirqs_off_thunk (apic_timer_interrupt) - <idle>-0 0d.s. 97us : __do_softirq (do_softirq) - <idle>-0 0d.s1 98us : trace_hardirqs_on (do_softirq) +# irqsoff latency trace v1.1.5 on 3.8.0-test+ +# -------------------------------------------------------------------- +# latency: 259 us, #4/4, CPU#2 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) +# ----------------- +# | task: ps-6143 (uid:0 nice:0 policy:0 rt_prio:0) +# ----------------- +# => started at: __lock_task_sighand +# => ended at: _raw_spin_unlock_irqrestore +# +# +# _------=> CPU# +# / _-----=> irqs-off +# | / _----=> need-resched +# || / _---=> hardirq/softirq +# ||| / _--=> preempt-depth +# |||| / delay +# cmd pid ||||| time | caller +# \ / ||||| \ | / + ps-6143 2d... 0us!: trace_hardirqs_off <-__lock_task_sighand + ps-6143 2d..1 259us+: trace_hardirqs_on <-_raw_spin_unlock_irqrestore + ps-6143 2d..1 263us+: time_hardirqs_on <-_raw_spin_unlock_irqrestore + ps-6143 2d..1 306us : <stack trace> + => trace_hardirqs_on_caller + => trace_hardirqs_on + => _raw_spin_unlock_irqrestore + => do_task_stat + => proc_tgid_stat + => proc_single_show + => seq_read + => vfs_read + => sys_read + => system_call_fastpath This shows that the current tracer is "irqsoff" tracing the time -for which interrupts were disabled. It gives the trace version -and the version of the kernel upon which this was executed on -(2.6.26-rc8). Then it displays the max latency in microsecs (97 -us). The number of trace entries displayed and the total number -recorded (both are three: #3/3). The type of preemption that was -used (PREEMPT). VP, KP, SP, and HP are always zero and are -reserved for later use. #P is the number of online CPUS (#P:2). +for which interrupts were disabled. It gives the trace version (which +never changes) and the version of the kernel upon which this was executed on +(3.10). Then it displays the max latency in microseconds (259 us). The number +of trace entries displayed and the total number (both are four: #4/4). +VP, KP, SP, and HP are always zero and are reserved for later use. +#P is the number of online CPUs (#P:4). The task is the process that was running when the latency -occurred. (swapper pid: 0). +occurred. (ps pid: 6143). The start and stop (the functions in which the interrupts were disabled and enabled respectively) that caused the latencies: - apic_timer_interrupt is where the interrupts were disabled. - do_softirq is where they were enabled again. + __lock_task_sighand is where the interrupts were disabled. + _raw_spin_unlock_irqrestore is where they were enabled again. The next lines after the header are the trace itself. The header explains which is which. @@ -367,16 +682,43 @@ The above is mostly meaningful for kernel developers. The rest is the same as the 'trace' file. + Note, the latency tracers will usually end with a back trace + to easily find where the latency occurred. trace_options ------------- -The trace_options file is used to control what gets printed in -the trace output. To see what is available, simply cat the file: +The trace_options file (or the options directory) is used to control +what gets printed in the trace output, or manipulate the tracers. +To see what is available, simply cat the file: cat trace_options - print-parent nosym-offset nosym-addr noverbose noraw nohex nobin \ - noblock nostacktrace nosched-tree nouserstacktrace nosym-userobj +print-parent +nosym-offset +nosym-addr +noverbose +noraw +nohex +nobin +noblock +nostacktrace +trace_printk +noftrace_preempt +nobranch +annotate +nouserstacktrace +nosym-userobj +noprintk-msg-only +context-info +latency-format +sleep-time +graph-time +record-cmd +overwrite +nodisable_on_free +irq-info +markers +function-trace To disable one of the options, echo in the option prepended with "no". @@ -428,13 +770,34 @@ Here are the available options: bin - This will print out the formats in raw binary. - block - TBD (needs update) + block - When set, reading trace_pipe will not block when polled. stacktrace - This is one of the options that changes the trace itself. When a trace is recorded, so is the stack of functions. This allows for back traces of trace sites. + trace_printk - Can disable trace_printk() from writing into the buffer. + + branch - Enable branch tracing with the tracer. + + annotate - It is sometimes confusing when the CPU buffers are full + and one CPU buffer had a lot of events recently, thus + a shorter time frame, were another CPU may have only had + a few events, which lets it have older events. When + the trace is reported, it shows the oldest events first, + and it may look like only one CPU ran (the one with the + oldest events). When the annotate option is set, it will + display when a new CPU buffer started: + + <idle>-0 [001] dNs4 21169.031481: wake_up_idle_cpu <-add_timer_on + <idle>-0 [001] dNs4 21169.031482: _raw_spin_unlock_irqrestore <-add_timer_on + <idle>-0 [001] .Ns4 21169.031484: sub_preempt_count <-_raw_spin_unlock_irqrestore +##### CPU 2 buffer started #### + <idle>-0 [002] .N.1 21169.031484: rcu_idle_exit <-cpu_idle + <idle>-0 [001] .Ns3 21169.031484: _raw_spin_unlock <-clocksource_watchdog + <idle>-0 [001] .Ns3 21169.031485: sub_preempt_count <-_raw_spin_unlock + userstacktrace - This option changes the trace. It records a stacktrace of the current userspace thread. @@ -451,9 +814,13 @@ Here are the available options: a.out-1623 [000] 40874.465068: /root/a.out[+0x480] <-/root/a.out[+0 x494] <- /root/a.out[+0x4a8] <- /lib/libc-2.7.so[+0x1e1a6] - sched-tree - trace all tasks that are on the runqueue, at - every scheduling event. Will add overhead if - there's a lot of tasks running at once. + + printk-msg-only - When set, trace_printk()s will only show the format + and not their parameters (if trace_bprintk() or + trace_bputs() was used to save the trace_printk()). + + context-info - Show only the event data. Hides the comm, PID, + timestamp, CPU, and other useful data. latency-format - This option changes the trace. When it is enabled, the trace displays @@ -461,31 +828,61 @@ x494] <- /root/a.out[+0x4a8] <- /lib/libc-2.7.so[+0x1e1a6] latencies, as described in "Latency trace format". + sleep-time - When running function graph tracer, to include + the time a task schedules out in its function. + When enabled, it will account time the task has been + scheduled out as part of the function call. + + graph-time - When running function graph tracer, to include the + time to call nested functions. When this is not set, + the time reported for the function will only include + the time the function itself executed for, not the time + for functions that it called. + + record-cmd - When any event or tracer is enabled, a hook is enabled + in the sched_switch trace point to fill comm cache + with mapped pids and comms. But this may cause some + overhead, and if you only care about pids, and not the + name of the task, disabling this option can lower the + impact of tracing. + overwrite - This controls what happens when the trace buffer is full. If "1" (default), the oldest events are discarded and overwritten. If "0", then the newest events are discarded. + (see per_cpu/cpu0/stats for overrun and dropped) -ftrace_enabled --------------- + disable_on_free - When the free_buffer is closed, tracing will + stop (tracing_on set to 0). -The following tracers (listed below) give different output -depending on whether or not the sysctl ftrace_enabled is set. To -set ftrace_enabled, one can either use the sysctl function or -set it via the proc file system interface. + irq-info - Shows the interrupt, preempt count, need resched data. + When disabled, the trace looks like: - sysctl kernel.ftrace_enabled=1 +# tracer: function +# +# entries-in-buffer/entries-written: 144405/9452052 #P:4 +# +# TASK-PID CPU# TIMESTAMP FUNCTION +# | | | | | + <idle>-0 [002] 23636.756054: ttwu_do_activate.constprop.89 <-try_to_wake_up + <idle>-0 [002] 23636.756054: activate_task <-ttwu_do_activate.constprop.89 + <idle>-0 [002] 23636.756055: enqueue_task <-activate_task - or - echo 1 > /proc/sys/kernel/ftrace_enabled + markers - When set, the trace_marker is writable (only by root). + When disabled, the trace_marker will error with EINVAL + on write. + + + function-trace - The latency tracers will enable function tracing + if this option is enabled (default it is). When + it is disabled, the latency tracers do not trace + functions. This keeps the overhead of the tracer down + when performing latency tests. -To disable ftrace_enabled simply replace the '1' with '0' in the -above commands. + Note: Some tracers have their own options. They only appear + when the tracer is active. -When ftrace_enabled is set the tracers will also record the -functions that are within the trace. The descriptions of the -tracers will also show an example with ftrace enabled. irqsoff @@ -506,95 +903,133 @@ new trace is saved. To reset the maximum, echo 0 into tracing_max_latency. Here is an example: + # echo 0 > options/function-trace # echo irqsoff > current_tracer - # echo latency-format > trace_options - # echo 0 > tracing_max_latency # echo 1 > tracing_on + # echo 0 > tracing_max_latency # ls -ltr [...] # echo 0 > tracing_on # cat trace # tracer: irqsoff # -irqsoff latency trace v1.1.5 on 2.6.26 --------------------------------------------------------------------- - latency: 12 us, #3/3, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:2) - ----------------- - | task: bash-3730 (uid:0 nice:0 policy:0 rt_prio:0) - ----------------- |