diff options
| -rw-r--r-- | Documentation/trace/timerlat-tracer.rst | 78 | ||||
| -rw-r--r-- | kernel/trace/trace_osnoise.c | 378 | ||||
| -rw-r--r-- | kernel/trace/trace_output.c | 4 |
3 files changed, 455 insertions, 5 deletions
diff --git a/Documentation/trace/timerlat-tracer.rst b/Documentation/trace/timerlat-tracer.rst index db17df312bc8..53a56823e903 100644 --- a/Documentation/trace/timerlat-tracer.rst +++ b/Documentation/trace/timerlat-tracer.rst @@ -180,3 +180,81 @@ dummy_load_1ms_pd_init, which had the following code (on purpose):: return 0; } + +User-space interface +--------------------------- + +Timerlat allows user-space threads to use timerlat infra-structure to +measure scheduling latency. This interface is accessible via a per-CPU +file descriptor inside $tracing_dir/osnoise/per_cpu/cpu$ID/timerlat_fd. + +This interface is accessible under the following conditions: + + - timerlat tracer is enable + - osnoise workload option is set to NO_OSNOISE_WORKLOAD + - The user-space thread is affined to a single processor + - The thread opens the file associated with its single processor + - Only one thread can access the file at a time + +The open() syscall will fail if any of these conditions are not met. +After opening the file descriptor, the user space can read from it. + +The read() system call will run a timerlat code that will arm the +timer in the future and wait for it as the regular kernel thread does. + +When the timer IRQ fires, the timerlat IRQ will execute, report the +IRQ latency and wake up the thread waiting in the read. The thread will be +scheduled and report the thread latency via tracer - as for the kernel +thread. + +The difference from the in-kernel timerlat is that, instead of re-arming +the timer, timerlat will return to the read() system call. At this point, +the user can run any code. + +If the application rereads the file timerlat file descriptor, the tracer +will report the return from user-space latency, which is the total +latency. If this is the end of the work, it can be interpreted as the +response time for the request. + +After reporting the total latency, timerlat will restart the cycle, arm +a timer, and go to sleep for the following activation. + +If at any time one of the conditions is broken, e.g., the thread migrates +while in user space, or the timerlat tracer is disabled, the SIG_KILL +signal will be sent to the user-space thread. + +Here is an basic example of user-space code for timerlat:: + + int main(void) + { + char buffer[1024]; + int timerlat_fd; + int retval; + long cpu = 0; /* place in CPU 0 */ + cpu_set_t set; + + CPU_ZERO(&set); + CPU_SET(cpu, &set); + + if (sched_setaffinity(gettid(), sizeof(set), &set) == -1) + return 1; + + snprintf(buffer, sizeof(buffer), + "/sys/kernel/tracing/osnoise/per_cpu/cpu%ld/timerlat_fd", + cpu); + + timerlat_fd = open(buffer, O_RDONLY); + if (timerlat_fd < 0) { + printf("error opening %s: %s\n", buffer, strerror(errno)); + exit(1); + } + + for (;;) { + retval = read(timerlat_fd, buffer, 1024); + if (retval < 0) + break; + } + + close(timerlat_fd); + exit(0); + } diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c index 220172cb874d..bd0d01d00fb9 100644 --- a/kernel/trace/trace_osnoise.c +++ b/kernel/trace/trace_osnoise.c @@ -181,6 +181,7 @@ struct osn_irq { #define IRQ_CONTEXT 0 #define THREAD_CONTEXT 1 +#define THREAD_URET 2 /* * sofirq runtime info. */ @@ -238,6 +239,7 @@ struct timerlat_variables { u64 abs_period; bool tracing_thread; u64 count; + bool uthread_migrate; }; static DEFINE_PER_CPU(struct timerlat_variables, per_cpu_timerlat_var); @@ -1181,6 +1183,78 @@ thread_exit(struct osnoise_variables *osn_var, struct task_struct *t) osn_var->thread.arrival_time = 0; } +#ifdef CONFIG_TIMERLAT_TRACER +/* + * osnoise_stop_exception - Stop tracing and the tracer. + */ +static __always_inline void osnoise_stop_exception(char *msg, int cpu) +{ + struct osnoise_instance *inst; + struct trace_array *tr; + + rcu_read_lock(); + list_for_each_entry_rcu(inst, &osnoise_instances, list) { + tr = inst->tr; + trace_array_printk_buf(tr->array_buffer.buffer, _THIS_IP_, + "stop tracing hit on cpu %d due to exception: %s\n", + smp_processor_id(), + msg); + + if (test_bit(OSN_PANIC_ON_STOP, &osnoise_options)) + panic("tracer hit on cpu %d due to exception: %s\n", + smp_processor_id(), + msg); + + tracer_tracing_off(tr); + } + rcu_read_unlock(); +} + +/* + * trace_sched_migrate_callback - sched:sched_migrate_task trace event handler + * + * his function is hooked to the sched:sched_migrate_task trace event, and monitors + * timerlat user-space thread migration. + */ +static void trace_sched_migrate_callback(void *data, struct task_struct *p, int dest_cpu) +{ + struct osnoise_variables *osn_var; + long cpu = task_cpu(p); + + osn_var = per_cpu_ptr(&per_cpu_osnoise_var, cpu); + if (osn_var->pid == p->pid && dest_cpu != cpu) { + per_cpu_ptr(&per_cpu_timerlat_var, cpu)->uthread_migrate = 1; + osnoise_taint("timerlat user-thread migrated\n"); + osnoise_stop_exception("timerlat user-thread migrated", cpu); + } +} + +static int register_migration_monitor(void) +{ + int ret = 0; + + /* + * Timerlat thread migration check is only required when running timerlat in user-space. + * Thus, enable callback only if timerlat is set with no workload. + */ + if (timerlat_enabled() && !test_bit(OSN_WORKLOAD, &osnoise_options)) + ret = register_trace_sched_migrate_task(trace_sched_migrate_callback, NULL); + + return ret; +} + +static void unregister_migration_monitor(void) +{ + if (timerlat_enabled() && !test_bit(OSN_WORKLOAD, &osnoise_options)) + unregister_trace_sched_migrate_task(trace_sched_migrate_callback, NULL); +} +#else +static int register_migration_monitor(void) +{ + return 0; +} +static void unregister_migration_monitor(void) {} +#endif /* * trace_sched_switch - sched:sched_switch trace event handler * @@ -1204,7 +1278,7 @@ trace_sched_switch_callback(void *data, bool preempt, } /* - * hook_thread_events - Hook the insturmentation for thread noise + * hook_thread_events - Hook the instrumentation for thread noise * * Hook the osnoise tracer callbacks to handle the noise from other * threads on the necessary kernel events. @@ -1217,11 +1291,19 @@ static int hook_thread_events(void) if (ret) return -EINVAL; + ret = register_migration_monitor(); + if (ret) + goto out_unreg; + return 0; + +out_unreg: + unregister_trace_sched_switch(trace_sched_switch_callback, NULL); + return -EINVAL; } /* - * unhook_thread_events - *nhook the insturmentation for thread noise + * unhook_thread_events - unhook the instrumentation for thread noise * * Unook the osnoise tracer callbacks to handle the noise from other * threads on the necessary kernel events. @@ -1229,6 +1311,7 @@ static int hook_thread_events(void) static void unhook_thread_events(void) { unregister_trace_sched_switch(trace_sched_switch_callback, NULL); + unregister_migration_monitor(); } /* @@ -1864,10 +1947,24 @@ static void stop_kthread(unsigned int cpu) kthread = per_cpu(per_cpu_osnoise_var, cpu).kthread; if (kthread) { - kthread_stop(kthread); + if (test_bit(OSN_WORKLOAD, &osnoise_options)) { + kthread_stop(kthread); + } else { + /* + * This is a user thread waiting on the timerlat_fd. We need + * to close all users, and the best way to guarantee this is + * by killing the thread. NOTE: this is a purpose specific file. + */ + kill_pid(kthread->thread_pid, SIGKILL, 1); + put_task_struct(kthread); + } per_cpu(per_cpu_osnoise_var, cpu).kthread = NULL; } else { + /* if no workload, just return */ if (!test_bit(OSN_WORKLOAD, &osnoise_options)) { + /* + * This is set in the osnoise tracer case. + */ per_cpu(per_cpu_osnoise_var, cpu).sampling = false; barrier(); return; @@ -1912,7 +2009,6 @@ static int start_kthread(unsigned int cpu) barrier(); return 0; } - snprintf(comm, 24, "osnoise/%d", cpu); } @@ -1941,6 +2037,11 @@ static int start_per_cpu_kthreads(void) int retval = 0; int cpu; + if (!test_bit(OSN_WORKLOAD, &osnoise_options)) { + if (timerlat_enabled()) + return 0; + } + cpus_read_lock(); /* * Run only on online CPUs in which osnoise is allowed to run. @@ -2281,6 +2382,223 @@ err_free: return err; } +#ifdef CONFIG_TIMERLAT_TRACER +static int timerlat_fd_open(struct inode *inode, struct file *file) +{ + struct osnoise_variables *osn_var; + struct timerlat_variables *tlat; + long cpu = (long) inode->i_cdev; + + mutex_lock(&interface_lock); + + /* + * This file is accessible only if timerlat is enabled, and + * NO_OSNOISE_WORKLOAD is set. + */ + if (!timerlat_enabled() || test_bit(OSN_WORKLOAD, &osnoise_options)) { + mutex_unlock(&interface_lock); + return -EINVAL; + } + + migrate_disable(); + + osn_var = this_cpu_osn_var(); + + /* + * The osn_var->pid holds the single access to this file. + */ + if (osn_var->pid) { + mutex_unlock(&interface_lock); + migrate_enable(); + return -EBUSY; + } + + /* + * timerlat tracer is a per-cpu tracer. Check if the user-space too + * is pinned to a single CPU. The tracer laters monitor if the task + * migrates and then disables tracer if it does. However, it is + * worth doing this basic acceptance test to avoid obviusly wrong + * setup. + */ + if (current->nr_cpus_allowed > 1 || cpu != smp_processor_id()) { + mutex_unlock(&interface_lock); + migrate_enable(); + return -EPERM; + } + + /* + * From now on, it is good to go. + */ + file->private_data = inode->i_cdev; + + get_task_struct(current); + + osn_var->kthread = current; + osn_var->pid = current->pid; + + /* + * Setup is done. + */ + mutex_unlock(&interface_lock); + + tlat = this_cpu_tmr_var(); + tlat->count = 0; + + migrate_enable(); + return 0; +}; + +/* + * timerlat_fd_read - Read function for "timerlat_fd" file + * @file: The active open file structure + * @ubuf: The userspace provided buffer to read value into + * @cnt: The maximum number of bytes to read + * @ppos: The current "file" position + * + * Prints 1 on timerlat, the number of interferences on osnoise, -1 on error. + */ +static ssize_t +timerlat_fd_read(struct file *file, char __user *ubuf, size_t count, + loff_t *ppos) +{ + long cpu = (long) file->private_data; + struct osnoise_variables *osn_var; + struct timerlat_variables *tlat; + struct timerlat_sample s; + s64 diff; + u64 now; + + migrate_disable(); + + tlat = this_cpu_tmr_var(); + + /* + * While in user-space, the thread is migratable. There is nothing + * we can do about it. + * So, if the thread is running on another CPU, stop the machinery. + */ + if (cpu == smp_processor_id()) { + if (tlat->uthread_migrate) { + migrate_enable(); + return -EINVAL; + } + } else { + per_cpu_ptr(&per_cpu_timerlat_var, cpu)->uthread_migrate = 1; + osnoise_taint("timerlat user thread migrate\n"); + osnoise_stop_tracing(); + migrate_enable(); + return -EINVAL; + } + + osn_var = this_cpu_osn_var(); + + /* + * The timerlat in user-space runs in a different order: + * the read() starts from the execution of the previous occurrence, + * sleeping for the next occurrence. + * + * So, skip if we are entering on read() before the first wakeup + * from timerlat IRQ: + */ + if (likely(osn_var->sampling)) { + now = ktime_to_ns(hrtimer_cb_get_time(&tlat->timer)); + diff = now - tlat->abs_period; + + /* + * it was not a timer firing, but some other signal? + */ + if (diff < 0) + goto out; + + s.seqnum = tlat->count; + s.timer_latency = diff; + s.context = THREAD_URET; + + trace_timerlat_sample(&s); + + notify_new_max_latency(diff); + + tlat->tracing_thread = false; + if (osnoise_data.stop_tracing_total) + if (time_to_us(diff) >= osnoise_data.stop_tracing_total) + osnoise_stop_tracing(); + } else { + tlat->tracing_thread = false; + tlat->kthread = current; + + hrtimer_init(&tlat->timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED_HARD); + tlat->timer.function = timerlat_irq; + + /* Annotate now to drift new period */ + tlat->abs_period = hrtimer_cb_get_time(&tlat->timer); + + osn_var->sampling = 1; + } + + /* wait for the next period */ + wait_next_period(tlat); + + /* This is the wakeup from this cycle */ + now = ktime_to_ns(hrtimer_cb_get_time(&tlat->timer)); + diff = now - tlat->abs_period; + + /* + * it was not a timer firing, but some other signal? + */ + if (diff < 0) + goto out; + + s.seqnum = tlat->count; + s.timer_latency = diff; + s.context = THREAD_CONTEXT; + + trace_timerlat_sample(&s); + + if (osnoise_data.stop_tracing_total) { + if (time_to_us(diff) >= osnoise_data.stop_tracing_total) { + timerlat_dump_stack(time_to_us(diff)); + notify_new_max_latency(diff); + osnoise_stop_tracing(); + } + } + +out: + migrate_enable(); + return 0; +} + +static int timerlat_fd_release(struct inode *inode, struct file *file) +{ + struct osnoise_variables *osn_var; + struct timerlat_variables *tlat_var; + long cpu = (long) file->private_data; + + migrate_disable(); + mutex_lock(&interface_lock); + + osn_var = per_cpu_ptr(&per_cpu_osnoise_var, cpu); + tlat_var = per_cpu_ptr(&per_cpu_timerlat_var, cpu); + + hrtimer_cancel(&tlat_var->timer); + memset(tlat_var, 0, sizeof(*tlat_var)); + + osn_var->sampling = 0; + osn_var->pid = 0; + + /* + * We are leaving, not being stopped... see stop_kthread(); + */ + if (osn_var->kthread) { + put_task_struct(osn_var->kthread); + osn_var->kthread = NULL; + } + + mutex_unlock(&interface_lock); + migrate_enable(); + return 0; +} +#endif + /* * osnoise/runtime_us: cannot be greater than the period. */ @@ -2344,6 +2662,13 @@ static struct trace_min_max_param timerlat_period = { .max = &timerlat_max_period, .min = &timerlat_min_period, }; + +static const struct file_operations timerlat_fd_fops = { + .open = timerlat_fd_open, + .read = timerlat_fd_read, + .release = timerlat_fd_release, + .llseek = generic_file_llseek, +}; #endif static const struct file_operations cpus_fops = { @@ -2381,18 +2706,63 @@ static int init_timerlat_stack_tracefs(struct dentry *top_dir) } #endif /* CONFIG_STACKTRACE */ +static int osnoise_create_cpu_timerlat_fd(struct dentry *top_dir) +{ + struct dentry *timerlat_fd; + struct dentry *per_cpu; + struct dentry *cpu_dir; + char cpu_str[30]; /* see trace.c: tracing_init_tracefs_percpu() */ + long cpu; + + /* + * Why not using tracing instance per_cpu/ dir? + * + * Because osnoise/timerlat have a single workload, having + * multiple files like these are wast of memory. + */ + per_cpu = tracefs_create_dir("per_cpu", top_dir); + if (!per_cpu) + return -ENOMEM; + + for_each_possible_cpu(cpu) { + snprintf(cpu_str, 30, "cpu%ld", cpu); + cpu_dir = tracefs_create_dir(cpu_str, per_cpu); + if (!cpu_dir) + goto out_clean; + + timerlat_fd = trace_create_file("timerlat_fd", TRACE_MODE_READ, + cpu_dir, NULL, &timerlat_fd_fops); + if (!timerlat_fd) + goto out_clean; + + /* Record the CPU */ + d_inode(timerlat_fd)->i_cdev = (void *)(cpu); + } + + return 0; + +out_clean: + tracefs_remove(per_cpu); + return -ENOMEM; +} + /* * init_timerlat_tracefs - A function to initialize the timerlat interface files */ static int init_timerlat_tracefs(struct dentry *top_dir) { struct dentry *tmp; + int retval; tmp = tracefs_create_file("timerlat_period_us", TRACE_MODE_WRITE, top_dir, &timerlat_period, &trace_min_max_fops); if (!tmp) return -ENOMEM; + retval = osnoise_create_cpu_timerlat_fd(top_dir); + if (retval) + return retval; + return init_timerlat_stack_tracefs(top_dir); } #else /* CONFIG_TIMERLAT_TRACER */ diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c index 15f05faaae44..9f10c0071c4f 100644 --- a/kernel/trace/trace_output.c +++ b/kernel/trace/trace_output.c @@ -1446,6 +1446,8 @@ static struct trace_event trace_osnoise_event = { }; /* TRACE_TIMERLAT */ + +static char *timerlat_lat_context[] = {"irq", "thread", "user-ret"}; static enum print_line_t trace_timerlat_print(struct trace_iterator *iter, int flags, struct trace_event *event) @@ -1458,7 +1460,7 @@ trace_timerlat_print(struct trace_iterator *iter, int flags, trace_seq_printf(s, "#%-5u context %6s timer_latency %9llu ns\n", field->seqnum, - field->context ? "thread" : "irq", + timerlat_lat_context[field->context], field->timer_latency); return trace_handle_return(s); |