diff options
Diffstat (limited to 'Documentation/trace/timerlat-tracer.rst')
| -rw-r--r-- | Documentation/trace/timerlat-tracer.rst | 24 |
1 files changed, 12 insertions, 12 deletions
diff --git a/Documentation/trace/timerlat-tracer.rst b/Documentation/trace/timerlat-tracer.rst index c7cbb557aee7..64d1fe6e9b93 100644 --- a/Documentation/trace/timerlat-tracer.rst +++ b/Documentation/trace/timerlat-tracer.rst @@ -3,7 +3,7 @@ Timerlat tracer ############### The timerlat tracer aims to help the preemptive kernel developers to -find souces of wakeup latencies of real-time threads. Like cyclictest, +find sources of wakeup latencies of real-time threads. Like cyclictest, the tracer sets a periodic timer that wakes up a thread. The thread then computes a *wakeup latency* value as the difference between the *current time* and the *absolute time* that the timer was set to expire. The main @@ -50,14 +50,14 @@ The second is the *timer latency* observed by the thread. The ACTIVATION ID field serves to relate the *irq* execution to its respective *thread* execution. -The *irq*/*thread* splitting is important to clarify at which context +The *irq*/*thread* splitting is important to clarify in which context the unexpected high value is coming from. The *irq* context can be -delayed by hardware related actions, such as SMIs, NMIs, IRQs -or by a thread masking interrupts. Once the timer happens, the delay +delayed by hardware-related actions, such as SMIs, NMIs, IRQs, +or by thread masking interrupts. Once the timer happens, the delay can also be influenced by blocking caused by threads. For example, by -postponing the scheduler execution via preempt_disable(), by the -scheduler execution, or by masking interrupts. Threads can -also be delayed by the interference from other threads and IRQs. +postponing the scheduler execution via preempt_disable(), scheduler +execution, or masking interrupts. Threads can also be delayed by the +interference from other threads and IRQs. Tracer options --------------------- @@ -68,14 +68,14 @@ directory. The timerlat configs are: - cpus: CPUs at which a timerlat thread will execute. - timerlat_period_us: the period of the timerlat thread. - - osnoise/stop_tracing_us: stop the system tracing if a + - stop_tracing_us: stop the system tracing if a timer latency at the *irq* context higher than the configured value happens. Writing 0 disables this option. - stop_tracing_total_us: stop the system tracing if a - timer latency at the *thread* context higher than the configured + timer latency at the *thread* context is higher than the configured value happens. Writing 0 disables this option. - - print_stack: save the stack of the IRQ ocurrence, and print - it afte the *thread context* event". + - print_stack: save the stack of the IRQ occurrence, and print + it after the *thread context* event". timerlat and osnoise ---------------------------- @@ -95,7 +95,7 @@ For example:: timerlat/5-1035 [005] ....... 548.771104: #402268 context thread timer_latency 39960 ns In this case, the root cause of the timer latency does not point to a -single cause, but to multiple ones. Firstly, the timer IRQ was delayed +single cause but to multiple ones. Firstly, the timer IRQ was delayed for 13 us, which may point to a long IRQ disabled section (see IRQ stacktrace section). Then the timer interrupt that wakes up the timerlat thread took 7597 ns, and the qxl:21 device IRQ took 7139 ns. Finally, |