Say N, unless you absolutely know what you are doing.
+config TRACEPOINT_BENCHMARK
+ bool "Add tracepoint that benchmarks tracepoints"
+ help
+ This option creates the tracepoint "benchmark:benchmark_event".
+ When the tracepoint is enabled, it kicks off a kernel thread that
+ goes into an infinite loop (calling cond_sched() to let other tasks
+ run), and calls the tracepoint. Each iteration will record the time
+ it took to write to the tracepoint and the next iteration that
+ data will be passed to the tracepoint itself. That is, the tracepoint
+ will report the time it took to do the previous tracepoint.
+ The string written to the tracepoint is a static string of 128 bytes
+ to keep the time the same. The initial string is simply a write of
+ "START". The second string records the cold cache time of the first
+ write which is not added to the rest of the calculations.
+
+ As it is a tight loop, it benchmarks as hot cache. That's fine because
+ we care most about hot paths that are probably in cache already.
+
+ An example of the output:
+
+ START
+ first=3672 [COLD CACHED]
+ last=632 first=3672 max=632 min=632 avg=316 std=446 std^2=199712
+ last=278 first=3672 max=632 min=278 avg=303 std=316 std^2=100337
+ last=277 first=3672 max=632 min=277 avg=296 std=258 std^2=67064
+ last=273 first=3672 max=632 min=273 avg=292 std=224 std^2=50411
+ last=273 first=3672 max=632 min=273 avg=288 std=200 std^2=40389
+ last=281 first=3672 max=632 min=273 avg=287 std=183 std^2=33666
+
+
config RING_BUFFER_BENCHMARK
tristate "Ring buffer benchmark stress tester"
depends on RING_BUFFER
--- /dev/null
+#include <linux/delay.h>
+#include <linux/module.h>
+#include <linux/kthread.h>
+#include <linux/trace_clock.h>
+
+#define CREATE_TRACE_POINTS
+#include "trace_benchmark.h"
+
+static struct task_struct *bm_event_thread;
+
+static char bm_str[BENCHMARK_EVENT_STRLEN] = "START";
+
+static u64 bm_total;
+static u64 bm_totalsq;
+static u64 bm_last;
+static u64 bm_max;
+static u64 bm_min;
+static u64 bm_first;
+static s64 bm_cnt;
+
+/*
+ * This gets called in a loop recording the time it took to write
+ * the tracepoint. What it writes is the time statistics of the last
+ * tracepoint write. As there is nothing to write the first time
+ * it simply writes "START". As the first write is cold cache and
+ * the rest is hot, we save off that time in bm_first and it is
+ * reported as "first", which is shown in the second write to the
+ * tracepoint. The "first" field is writen within the statics from
+ * then on but never changes.
+ */
+static void trace_do_benchmark(void)
+{
+ u64 start;
+ u64 stop;
+ u64 delta;
+ s64 stddev;
+ u64 seed;
+ u64 seedsq;
+ u64 last_seed;
+ unsigned int avg;
+ unsigned int std = 0;
+
+ /* Only run if the tracepoint is actually active */
+ if (!trace_benchmark_event_enabled())
+ return;
+
+ local_irq_disable();
+ start = trace_clock_local();
+ trace_benchmark_event(bm_str);
+ stop = trace_clock_local();
+ local_irq_enable();
+
+ bm_cnt++;
+
+ delta = stop - start;
+
+ /*
+ * The first read is cold cached, keep it separate from the
+ * other calculations.
+ */
+ if (bm_cnt == 1) {
+ bm_first = delta;
+ scnprintf(bm_str, BENCHMARK_EVENT_STRLEN,
+ "first=%llu [COLD CACHED]", bm_first);
+ return;
+ }
+
+ bm_last = delta;
+
+ bm_total += delta;
+ bm_totalsq += delta * delta;
+
+ if (delta > bm_max)
+ bm_max = delta;
+ if (!bm_min || delta < bm_min)
+ bm_min = delta;
+
+ if (bm_cnt > 1) {
+ /*
+ * Apply Welford's method to calculate standard deviation:
+ * s^2 = 1 / (n * (n-1)) * (n * \Sum (x_i)^2 - (\Sum x_i)^2)
+ */
+ stddev = (u64)bm_cnt * bm_totalsq - bm_total * bm_total;
+ do_div(stddev, bm_cnt);
+ do_div(stddev, bm_cnt - 1);
+ } else
+ stddev = 0;
+
+ delta = bm_total;
+ do_div(delta, bm_cnt);
+ avg = delta;
+
+ if (stddev > 0) {
+ int i = 0;
+ /*
+ * stddev is the square of standard deviation but
+ * we want the actualy number. Use the average
+ * as our seed to find the std.
+ *
+ * The next try is:
+ * x = (x + N/x) / 2
+ *
+ * Where N is the squared number to find the square
+ * root of.
+ */
+ seed = avg;
+ do {
+ last_seed = seed;
+ seed = stddev;
+ if (!last_seed)
+ break;
+ do_div(seed, last_seed);
+ seed += last_seed;
+ do_div(seed, 2);
+ } while (i++ < 10 && last_seed != seed);
+
+ std = seed;
+ }
+
+ scnprintf(bm_str, BENCHMARK_EVENT_STRLEN,
+ "last=%llu first=%llu max=%llu min=%llu avg=%u std=%d std^2=%lld",
+ bm_last, bm_first, bm_max, bm_min, avg, std, stddev);
+}
+
+static int benchmark_event_kthread(void *arg)
+{
+ /* sleep a bit to make sure the tracepoint gets activated */
+ msleep(100);
+
+ while (!kthread_should_stop()) {
+
+ trace_do_benchmark();
+
+ /*
+ * We don't go to sleep, but let others
+ * run as well.
+ */
+ cond_resched();
+ }
+
+ return 0;
+}
+
+/*
+ * When the benchmark tracepoint is enabled, it calls this
+ * function and the thread that calls the tracepoint is created.
+ */
+void trace_benchmark_reg(void)
+{
+ bm_event_thread = kthread_run(benchmark_event_kthread,
+ NULL, "event_benchmark");
+ WARN_ON(!bm_event_thread);
+}
+
+/*
+ * When the benchmark tracepoint is disabled, it calls this
+ * function and the thread that calls the tracepoint is deleted
+ * and all the numbers are reset.
+ */
+void trace_benchmark_unreg(void)
+{
+ if (!bm_event_thread)
+ return;
+
+ kthread_stop(bm_event_thread);
+
+ strcpy(bm_str, "START");
+ bm_total = 0;
+ bm_totalsq = 0;
+ bm_last = 0;
+ bm_max = 0;
+ bm_min = 0;
+ bm_cnt = 0;
+ /* bm_first doesn't need to be reset but reset it anyway */
+ bm_first = 0;
+}
--- /dev/null
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM benchmark
+
+#if !defined(_TRACE_BENCHMARK_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_BENCHMARK_H
+
+#include <linux/tracepoint.h>
+
+extern void trace_benchmark_reg(void);
+extern void trace_benchmark_unreg(void);
+
+#define BENCHMARK_EVENT_STRLEN 128
+
+TRACE_EVENT_FN(benchmark_event,
+
+ TP_PROTO(const char *str),
+
+ TP_ARGS(str),
+
+ TP_STRUCT__entry(
+ __array( char, str, BENCHMARK_EVENT_STRLEN )
+ ),
+
+ TP_fast_assign(
+ memcpy(__entry->str, str, BENCHMARK_EVENT_STRLEN);
+ ),
+
+ TP_printk("%s", __entry->str),
+
+ trace_benchmark_reg, trace_benchmark_unreg
+);
+
+#endif /* _TRACE_BENCHMARK_H */
+
+#undef TRACE_INCLUDE_FILE
+#undef TRACE_INCLUDE_PATH
+#define TRACE_INCLUDE_PATH .
+#define TRACE_INCLUDE_FILE trace_benchmark
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
projects / linux-2.6-microblaze.git / commitdiff