From patchwork Tue Jan 3 12:49:12 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mark Rutland X-Patchwork-Id: 13087445 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id AE65FC4708E for ; Tue, 3 Jan 2023 12:54:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233189AbjACMyt (ORCPT ); Tue, 3 Jan 2023 07:54:49 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41614 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237633AbjACMte (ORCPT ); Tue, 3 Jan 2023 07:49:34 -0500 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id C7FE7BF7; Tue, 3 Jan 2023 04:49:32 -0800 (PST) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 438D51570; Tue, 3 Jan 2023 04:50:14 -0800 (PST) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id B11173F587; Tue, 3 Jan 2023 04:49:31 -0800 (PST) From: Mark Rutland To: linux-kernel@vger.kernel.org Cc: mark.rutland@arm.com, mhiramat@kernel.org, revest@chromium.org, rostedt@goodmis.org, linux-trace-kernel@vger.kernel.org Subject: [PATCH v2 3/3] ftrace: Add sample with custom ops Date: Tue, 3 Jan 2023 12:49:12 +0000 Message-Id: <20230103124912.2948963-4-mark.rutland@arm.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20230103124912.2948963-1-mark.rutland@arm.com> References: <20230103124912.2948963-1-mark.rutland@arm.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-trace-kernel@vger.kernel.org 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) Signed-off-by: Mark Rutland Cc: Florent Revest Cc: Masami Hiramatsu Cc: Steven Rostedt Acked-by: Masami Hiramatsu (Google) --- samples/Kconfig | 7 + samples/Makefile | 1 + samples/ftrace/Makefile | 1 + samples/ftrace/ftrace-ops.c | 252 ++++++++++++++++++++++++++++++++++++ 4 files changed, 261 insertions(+) create mode 100644 samples/ftrace/ftrace-ops.c diff --git a/samples/Kconfig b/samples/Kconfig index 0d81c00289ee3..daf14c35f071d 100644 --- a/samples/Kconfig +++ b/samples/Kconfig @@ -46,6 +46,13 @@ config SAMPLE_FTRACE_DIRECT_MULTI that hooks to wake_up_process and schedule, and prints the function addresses. +config SAMPLE_FTRACE_OPS + tristate "Build custom ftrace ops example" + depends on FUNCTION_TRACER + help + This builds an ftrace ops example that hooks two functions and + measures the time taken to invoke one function a number of times. + config SAMPLE_TRACE_ARRAY tristate "Build sample module for kernel access to Ftrace instancess" depends on EVENT_TRACING && m diff --git a/samples/Makefile b/samples/Makefile index 9832ef3f8fcba..7cb632ef88eeb 100644 --- a/samples/Makefile +++ b/samples/Makefile @@ -24,6 +24,7 @@ obj-$(CONFIG_SAMPLE_TRACE_CUSTOM_EVENTS) += trace_events/ obj-$(CONFIG_SAMPLE_TRACE_PRINTK) += trace_printk/ obj-$(CONFIG_SAMPLE_FTRACE_DIRECT) += ftrace/ obj-$(CONFIG_SAMPLE_FTRACE_DIRECT_MULTI) += ftrace/ +obj-$(CONFIG_SAMPLE_FTRACE_OPS) += ftrace/ obj-$(CONFIG_SAMPLE_TRACE_ARRAY) += ftrace/ subdir-$(CONFIG_SAMPLE_UHID) += uhid obj-$(CONFIG_VIDEO_PCI_SKELETON) += v4l/ diff --git a/samples/ftrace/Makefile b/samples/ftrace/Makefile index faf8cdb79c5f4..589baf2ec4e3d 100644 --- a/samples/ftrace/Makefile +++ b/samples/ftrace/Makefile @@ -5,6 +5,7 @@ obj-$(CONFIG_SAMPLE_FTRACE_DIRECT) += ftrace-direct-too.o obj-$(CONFIG_SAMPLE_FTRACE_DIRECT) += ftrace-direct-modify.o obj-$(CONFIG_SAMPLE_FTRACE_DIRECT_MULTI) += ftrace-direct-multi.o obj-$(CONFIG_SAMPLE_FTRACE_DIRECT_MULTI) += ftrace-direct-multi-modify.o +obj-$(CONFIG_SAMPLE_FTRACE_OPS) += ftrace-ops.o CFLAGS_sample-trace-array.o := -I$(src) obj-$(CONFIG_SAMPLE_TRACE_ARRAY) += sample-trace-array.o diff --git a/samples/ftrace/ftrace-ops.c b/samples/ftrace/ftrace-ops.c new file mode 100644 index 0000000000000..24deb51c72618 --- /dev/null +++ b/samples/ftrace/ftrace-ops.c @@ -0,0 +1,252 @@ +// SPDX-License-Identifier: GPL-2.0-only + +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt + +#include +#include +#include + +#include + +/* + * Arbitrary large value chosen to be sufficiently large to minimize noise but + * sufficiently small to complete quickly. + */ +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. + */ +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. + */ +unsigned int nr_ops_irrelevant = 0; +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. + */ +bool save_regs = false; +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)"); + +bool assist_recursion = false; +module_param(assist_recursion, bool, 0); +MODULE_PARM_DESC(assist_reursion, "Register ops with FTRACE_OPS_FL_RECURSION"); + +bool assist_rcu = false; +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. + */ +bool check_count = false; +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. + */ +bool persist = false; +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++; +} + +struct sample_ops *ops_relevant; +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); + } +} + +ftrace_func_t tracer_relevant = ops_func_nop; +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, 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");