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ftrace: Add sample with custom ops
When reworking core ftrace code or architectural ftrace code, it's often necessary to test/analyse/benchmark a number of ftrace_ops configurations. This patch adds a module which can be used to explore some of those configurations. I'm using this to benchmark various options for changing the way trampolines and handling of ftrace_ops work on arm64, and ensuring other architectures aren't adversely affected. For example, in a QEMU+KVM VM running on a 2GHz Xeon E5-2660 workstation, loading the module in various configurations produces: | # insmod ftrace-ops.ko | ftrace_ops: registering: | relevant ops: 1 | tracee: tracee_relevant [ftrace_ops] | tracer: ops_func_nop [ftrace_ops] | irrelevant ops: 0 | tracee: tracee_irrelevant [ftrace_ops] | tracer: ops_func_nop [ftrace_ops] | saving registers: NO | assist recursion: NO | assist RCU: NO | ftrace_ops: Attempted 100000 calls to tracee_relevant [ftrace_ops] in 1681558ns (16ns / call) | # insmod ftrace-ops.ko nr_ops_irrelevant=5 | ftrace_ops: registering: | relevant ops: 1 | tracee: tracee_relevant [ftrace_ops] | tracer: ops_func_nop [ftrace_ops] | irrelevant ops: 5 | tracee: tracee_irrelevant [ftrace_ops] | tracer: ops_func_nop [ftrace_ops] | saving registers: NO | assist recursion: NO | assist RCU: NO | ftrace_ops: Attempted 100000 calls to tracee_relevant [ftrace_ops] in 1693042ns (16ns / call) | # insmod ftrace-ops.ko nr_ops_relevant=2 | ftrace_ops: registering: | relevant ops: 2 | tracee: tracee_relevant [ftrace_ops] | tracer: ops_func_nop [ftrace_ops] | irrelevant ops: 0 | tracee: tracee_irrelevant [ftrace_ops] | tracer: ops_func_nop [ftrace_ops] | saving registers: NO | assist recursion: NO | assist RCU: NO | ftrace_ops: Attempted 100000 calls to tracee_relevant [ftrace_ops] in 11965582ns (119ns / call) | # insmod ftrace-ops.ko save_regs=true | ftrace_ops: registering: | relevant ops: 1 | tracee: tracee_relevant [ftrace_ops] | tracer: ops_func_nop [ftrace_ops] | irrelevant ops: 0 | tracee: tracee_irrelevant [ftrace_ops] | tracer: ops_func_nop [ftrace_ops] | saving registers: YES | assist recursion: NO | assist RCU: NO | ftrace_ops: Attempted 100000 calls to tracee_relevant [ftrace_ops] in 4459624ns (44ns / call) Link: https://lkml.kernel.org/r/20230103124912.2948963-4-mark.rutland@arm.com Cc: Florent Revest <revest@chromium.org> Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> Signed-off-by: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Mark Rutland
Steven Rostedt (Google)
parent
7f09d639b8
commit
b56c68f705
@ -46,6 +46,13 @@ config SAMPLE_FTRACE_DIRECT_MULTI
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that hooks to wake_up_process and schedule, and prints
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the function addresses.
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config SAMPLE_FTRACE_OPS
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tristate "Build custom ftrace ops example"
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depends on FUNCTION_TRACER
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help
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This builds an ftrace ops example that hooks two functions and
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measures the time taken to invoke one function a number of times.
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config SAMPLE_TRACE_ARRAY
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tristate "Build sample module for kernel access to Ftrace instancess"
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depends on EVENT_TRACING && m
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@ -24,6 +24,7 @@ obj-$(CONFIG_SAMPLE_TRACE_CUSTOM_EVENTS) += trace_events/
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obj-$(CONFIG_SAMPLE_TRACE_PRINTK) += trace_printk/
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obj-$(CONFIG_SAMPLE_FTRACE_DIRECT) += ftrace/
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obj-$(CONFIG_SAMPLE_FTRACE_DIRECT_MULTI) += ftrace/
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obj-$(CONFIG_SAMPLE_FTRACE_OPS) += ftrace/
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obj-$(CONFIG_SAMPLE_TRACE_ARRAY) += ftrace/
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subdir-$(CONFIG_SAMPLE_UHID) += uhid
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obj-$(CONFIG_VIDEO_PCI_SKELETON) += v4l/
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@ -5,6 +5,7 @@ obj-$(CONFIG_SAMPLE_FTRACE_DIRECT) += ftrace-direct-too.o
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obj-$(CONFIG_SAMPLE_FTRACE_DIRECT) += ftrace-direct-modify.o
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obj-$(CONFIG_SAMPLE_FTRACE_DIRECT_MULTI) += ftrace-direct-multi.o
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obj-$(CONFIG_SAMPLE_FTRACE_DIRECT_MULTI) += ftrace-direct-multi-modify.o
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obj-$(CONFIG_SAMPLE_FTRACE_OPS) += ftrace-ops.o
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CFLAGS_sample-trace-array.o := -I$(src)
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obj-$(CONFIG_SAMPLE_TRACE_ARRAY) += sample-trace-array.o
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252
samples/ftrace/ftrace-ops.c
Normal file
252
samples/ftrace/ftrace-ops.c
Normal file
@ -0,0 +1,252 @@
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// SPDX-License-Identifier: GPL-2.0-only
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/ftrace.h>
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#include <linux/ktime.h>
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#include <linux/module.h>
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#include <asm/barrier.h>
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/*
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* Arbitrary large value chosen to be sufficiently large to minimize noise but
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* sufficiently small to complete quickly.
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*/
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unsigned int nr_function_calls = 100000;
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module_param(nr_function_calls, uint, 0);
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MODULE_PARM_DESC(nr_function_calls, "How many times to call the relevant tracee");
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/*
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* The number of ops associated with a call site affects whether a tracer can
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* be called directly or whether it's necessary to go via the list func, which
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* can be significantly more expensive.
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*/
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unsigned int nr_ops_relevant = 1;
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module_param(nr_ops_relevant, uint, 0);
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MODULE_PARM_DESC(nr_ops_relevant, "How many ftrace_ops to associate with the relevant tracee");
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/*
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* On architectures where all call sites share the same trampoline, having
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* tracers enabled for distinct functions can force the use of the list func
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* and incur overhead for all call sites.
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*/
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unsigned int nr_ops_irrelevant = 0;
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module_param(nr_ops_irrelevant, uint, 0);
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MODULE_PARM_DESC(nr_ops_irrelevant, "How many ftrace_ops to associate with the irrelevant tracee");
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/*
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* On architectures with DYNAMIC_FTRACE_WITH_REGS, saving the full pt_regs can
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* be more expensive than only saving the minimal necessary regs.
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*/
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bool save_regs = false;
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module_param(save_regs, bool, 0);
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MODULE_PARM_DESC(save_regs, "Register ops with FTRACE_OPS_FL_SAVE_REGS (save all registers in the trampoline)");
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bool assist_recursion = false;
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module_param(assist_recursion, bool, 0);
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MODULE_PARM_DESC(assist_reursion, "Register ops with FTRACE_OPS_FL_RECURSION");
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bool assist_rcu = false;
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module_param(assist_rcu, bool, 0);
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MODULE_PARM_DESC(assist_reursion, "Register ops with FTRACE_OPS_FL_RCU");
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/*
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* By default, a trivial tracer is used which immediately returns to mimimize
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* overhead. Sometimes a consistency check using a more expensive tracer is
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* desireable.
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*/
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bool check_count = false;
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module_param(check_count, bool, 0);
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MODULE_PARM_DESC(check_count, "Check that tracers are called the expected number of times\n");
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/*
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* Usually it's not interesting to leave the ops registered after the test
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* runs, but sometimes it can be useful to leave them registered so that they
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* can be inspected through the tracefs 'enabled_functions' file.
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*/
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bool persist = false;
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module_param(persist, bool, 0);
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MODULE_PARM_DESC(persist, "Successfully load module and leave ftrace ops registered after test completes\n");
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/*
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* Marked as noinline to ensure that an out-of-line traceable copy is
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* generated by the compiler.
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*
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* The barrier() ensures the compiler won't elide calls by determining there
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* are no side-effects.
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*/
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static noinline void tracee_relevant(void)
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{
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barrier();
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}
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/*
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* Marked as noinline to ensure that an out-of-line traceable copy is
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* generated by the compiler.
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*
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* The barrier() ensures the compiler won't elide calls by determining there
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* are no side-effects.
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*/
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static noinline void tracee_irrelevant(void)
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{
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barrier();
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}
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struct sample_ops {
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struct ftrace_ops ops;
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unsigned int count;
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};
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static void ops_func_nop(unsigned long ip, unsigned long parent_ip,
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struct ftrace_ops *op,
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struct ftrace_regs *fregs)
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{
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/* do nothing */
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}
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static void ops_func_count(unsigned long ip, unsigned long parent_ip,
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struct ftrace_ops *op,
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struct ftrace_regs *fregs)
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{
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struct sample_ops *self;
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self = container_of(op, struct sample_ops, ops);
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self->count++;
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}
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struct sample_ops *ops_relevant;
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struct sample_ops *ops_irrelevant;
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static struct sample_ops *ops_alloc_init(void *tracee, ftrace_func_t func,
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unsigned long flags, int nr)
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{
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struct sample_ops *ops;
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ops = kcalloc(nr, sizeof(*ops), GFP_KERNEL);
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if (WARN_ON_ONCE(!ops))
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return NULL;
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for (unsigned int i = 0; i < nr; i++) {
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ops[i].ops.func = func;
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ops[i].ops.flags = flags;
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WARN_ON_ONCE(ftrace_set_filter_ip(&ops[i].ops, (unsigned long)tracee, 0, 0));
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WARN_ON_ONCE(register_ftrace_function(&ops[i].ops));
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}
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return ops;
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}
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static void ops_destroy(struct sample_ops *ops, int nr)
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{
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if (!ops)
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return;
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for (unsigned int i = 0; i < nr; i++) {
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WARN_ON_ONCE(unregister_ftrace_function(&ops[i].ops));
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ftrace_free_filter(&ops[i].ops);
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}
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kfree(ops);
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}
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static void ops_check(struct sample_ops *ops, int nr,
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unsigned int expected_count)
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{
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if (!ops || !check_count)
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return;
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for (unsigned int i = 0; i < nr; i++) {
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if (ops->count == expected_count)
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continue;
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pr_warn("Counter called %u times (expected %u)\n",
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ops->count, expected_count);
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}
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}
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ftrace_func_t tracer_relevant = ops_func_nop;
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ftrace_func_t tracer_irrelevant = ops_func_nop;
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static int __init ftrace_ops_sample_init(void)
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{
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unsigned long flags = 0;
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ktime_t start, end;
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u64 period;
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if (!IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS) && save_regs) {
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pr_info("this kernel does not support saving registers\n");
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save_regs = false;
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} else if (save_regs) {
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flags |= FTRACE_OPS_FL_SAVE_REGS;
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}
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if (assist_recursion)
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flags |= FTRACE_OPS_FL_RECURSION;
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if (assist_rcu)
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flags |= FTRACE_OPS_FL_RCU;
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if (check_count) {
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tracer_relevant = ops_func_count;
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tracer_irrelevant = ops_func_count;
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}
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pr_info("registering:\n"
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" relevant ops: %u\n"
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" tracee: %ps\n"
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" tracer: %ps\n"
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" irrelevant ops: %u\n"
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" tracee: %ps\n"
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" tracer: %ps\n"
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" saving registers: %s\n"
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" assist recursion: %s\n"
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" assist RCU: %s\n",
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nr_ops_relevant, tracee_relevant, tracer_relevant,
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nr_ops_irrelevant, tracee_irrelevant, tracer_irrelevant,
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save_regs ? "YES" : "NO",
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assist_recursion ? "YES" : "NO",
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assist_rcu ? "YES" : "NO");
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ops_relevant = ops_alloc_init(tracee_relevant, tracer_relevant,
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flags, nr_ops_relevant);
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ops_irrelevant = ops_alloc_init(tracee_irrelevant, tracer_irrelevant,
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flags, nr_ops_irrelevant);
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start = ktime_get();
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for (unsigned int i = 0; i < nr_function_calls; i++)
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tracee_relevant();
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end = ktime_get();
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ops_check(ops_relevant, nr_ops_relevant, nr_function_calls);
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ops_check(ops_irrelevant, nr_ops_irrelevant, 0);
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period = ktime_to_ns(ktime_sub(end, start));
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pr_info("Attempted %u calls to %ps in %lluns (%lluns / call)\n",
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nr_function_calls, tracee_relevant,
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period, period / nr_function_calls);
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if (persist)
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return 0;
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ops_destroy(ops_relevant, nr_ops_relevant);
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ops_destroy(ops_irrelevant, nr_ops_irrelevant);
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/*
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* The benchmark completed sucessfully, but there's no reason to keep
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* the module around. Return an error do the user doesn't have to
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* manually unload the module.
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*/
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return -EINVAL;
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}
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module_init(ftrace_ops_sample_init);
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static void __exit ftrace_ops_sample_exit(void)
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{
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ops_destroy(ops_relevant, nr_ops_relevant);
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ops_destroy(ops_irrelevant, nr_ops_irrelevant);
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}
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module_exit(ftrace_ops_sample_exit);
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MODULE_AUTHOR("Mark Rutland");
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MODULE_DESCRIPTION("Example of using custom ftrace_ops");
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MODULE_LICENSE("GPL");
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