// SPDX-License-Identifier: GPL-2.0-only
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/ftrace.h>
#include <linux/ktime.h>
#include <linux/module.h>
#include <asm/barrier.h>
/*
* Arbitrary large value chosen to be sufficiently large to minimize noise but
* sufficiently small to complete quickly.
*/
static unsigned int nr_function_calls = 100000;
module_param(nr_function_calls, uint, 0);
MODULE_PARM_DESC(nr_function_calls, "How many times to call the relevant tracee");
/*
* The number of ops associated with a call site affects whether a tracer can
* be called directly or whether it's necessary to go via the list func, which
* can be significantly more expensive.
*/
static unsigned int nr_ops_relevant = 1;
module_param(nr_ops_relevant, uint, 0);
MODULE_PARM_DESC(nr_ops_relevant, "How many ftrace_ops to associate with the relevant tracee");
/*
* On architectures where all call sites share the same trampoline, having
* tracers enabled for distinct functions can force the use of the list func
* and incur overhead for all call sites.
*/
static unsigned int nr_ops_irrelevant;
module_param(nr_ops_irrelevant, uint, 0);
MODULE_PARM_DESC(nr_ops_irrelevant, "How many ftrace_ops to associate with the irrelevant tracee");
/*
* On architectures with DYNAMIC_FTRACE_WITH_REGS, saving the full pt_regs can
* be more expensive than only saving the minimal necessary regs.
*/
static bool save_regs;
module_param(save_regs, bool, 0);
MODULE_PARM_DESC(save_regs, "Register ops with FTRACE_OPS_FL_SAVE_REGS (save all registers in the trampoline)");
static bool assist_recursion;
module_param(assist_recursion, bool, 0);
MODULE_PARM_DESC(assist_reursion, "Register ops with FTRACE_OPS_FL_RECURSION");
static bool assist_rcu;
module_param(assist_rcu, bool, 0);
MODULE_PARM_DESC(assist_reursion, "Register ops with FTRACE_OPS_FL_RCU");
/*
* By default, a trivial tracer is used which immediately returns to mimimize
* overhead. Sometimes a consistency check using a more expensive tracer is
* desireable.
*/
static bool check_count;
module_param(check_count, bool, 0);
MODULE_PARM_DESC(check_count, "Check that tracers are called the expected number of times\n");
/*
* Usually it's not interesting to leave the ops registered after the test
* runs, but sometimes it can be useful to leave them registered so that they
* can be inspected through the tracefs 'enabled_functions' file.
*/
static bool persist;
module_param(persist, bool, 0);
MODULE_PARM_DESC(persist, "Successfully load module and leave ftrace ops registered after test completes\n");
/*
* Marked as noinline to ensure that an out-of-line traceable copy is
* generated by the compiler.
*
* The barrier() ensures the compiler won't elide calls by determining there
* are no side-effects.
*/
static noinline void tracee_relevant(void)
{
barrier();
}
/*
* Marked as noinline to ensure that an out-of-line traceable copy is
* generated by the compiler.
*
* The barrier() ensures the compiler won't elide calls by determining there
* are no side-effects.
*/
static noinline void tracee_irrelevant(void)
{
barrier();
}
struct sample_ops {
struct ftrace_ops ops;
unsigned int count;
};
static void ops_func_nop(unsigned long ip, unsigned long parent_ip,
struct ftrace_ops *op,
struct ftrace_regs *fregs)
{
/* do nothing */
}
static void ops_func_count(unsigned long ip, unsigned long parent_ip,
struct ftrace_ops *op,
struct ftrace_regs *fregs)
{
struct sample_ops *self;
self = container_of(op, struct sample_ops, ops);
self->count++;
}
static struct sample_ops *ops_relevant;
static struct sample_ops *ops_irrelevant;
static struct sample_ops *ops_alloc_init(void *tracee, ftrace_func_t func,
unsigned long flags, int nr)
{
struct sample_ops *ops;
ops = kcalloc(nr, sizeof(*ops), GFP_KERNEL);
if (WARN_ON_ONCE(!ops))
return NULL;
for (unsigned int i = 0; i < nr; i++) {
ops[i].ops.func = func;
ops[i].ops.flags = flags;
WARN_ON_ONCE(ftrace_set_filter_ip(&ops[i].ops, (unsigned long)tracee, 0, 0));
WARN_ON_ONCE(register_ftrace_function(&ops[i].ops));
}
return ops;
}
static void ops_destroy(struct sample_ops *ops, int nr)
{
if (!ops)
return;
for (unsigned int i = 0; i < nr; i++) {
WARN_ON_ONCE(unregister_ftrace_function(&ops[i].ops));
ftrace_free_filter(&ops[i].ops);
}
kfree(ops);
}
static void ops_check(struct sample_ops *ops, int nr,
unsigned int expected_count)
{
if (!ops || !check_count)
return;
for (unsigned int i = 0; i < nr; i++) {
if (ops->count == expected_count)
continue;
pr_warn("Counter called %u times (expected %u)\n",
ops->count, expected_count);
}
}
static ftrace_func_t tracer_relevant = ops_func_nop;
static ftrace_func_t tracer_irrelevant = ops_func_nop;
static int __init ftrace_ops_sample_init(void)
{
unsigned long flags = 0;
ktime_t start, end;
u64 period;
if (!IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS) && save_regs) {
pr_info("this kernel does not support saving registers\n");
save_regs = false;
} else if (save_regs) {
flags |= FTRACE_OPS_FL_SAVE_REGS;
}
if (assist_recursion)
flags |= FTRACE_OPS_FL_RECURSION;
if (assist_rcu)
flags |= FTRACE_OPS_FL_RCU;
if (check_count) {
tracer_relevant = ops_func_count;
tracer_irrelevant = ops_func_count;
}
pr_info("registering:\n"
" relevant ops: %u\n"
" tracee: %ps\n"
" tracer: %ps\n"
" irrelevant ops: %u\n"
" tracee: %ps\n"
" tracer: %ps\n"
" saving registers: %s\n"
" assist recursion: %s\n"
" assist RCU: %s\n",
nr_ops_relevant, tracee_relevant, tracer_relevant,
nr_ops_irrelevant, tracee_irrelevant, tracer_irrelevant,
save_regs ? "YES" : "NO",
assist_recursion ? "YES" : "NO",
assist_rcu ? "YES" : "NO");
ops_relevant = ops_alloc_init(tracee_relevant, tracer_relevant,
flags, nr_ops_relevant);
ops_irrelevant = ops_alloc_init(tracee_irrelevant, tracer_irrelevant,
flags, nr_ops_irrelevant);
start = ktime_get();
for (unsigned int i = 0; i < nr_function_calls; i++)
tracee_relevant();
end = ktime_get();
ops_check(ops_relevant, nr_ops_relevant, nr_function_calls);
ops_check(ops_irrelevant, nr_ops_irrelevant, 0);
period = ktime_to_ns(ktime_sub(end, start));
pr_info("Attempted %u calls to %ps in %lluns (%lluns / call)\n",
nr_function_calls, tracee_relevant,
period, div_u64(period, nr_function_calls));
if (persist)
return 0;
ops_destroy(ops_relevant, nr_ops_relevant);
ops_destroy(ops_irrelevant, nr_ops_irrelevant);
/*
* The benchmark completed sucessfully, but there's no reason to keep
* the module around. Return an error do the user doesn't have to
* manually unload the module.
*/
return -EINVAL;
}
module_init(ftrace_ops_sample_init);
static void __exit ftrace_ops_sample_exit(void)
{
ops_destroy(ops_relevant, nr_ops_relevant);
ops_destroy(ops_irrelevant, nr_ops_irrelevant);
}
module_exit(ftrace_ops_sample_exit);
MODULE_AUTHOR("Mark Rutland");
MODULE_DESCRIPTION("Example of using custom ftrace_ops");
MODULE_LICENSE("GPL");
Codebase Browser
linux