Re: [RFC PATCH v3] ftrace: support very early function tracing
From: Abderrahmane Benbachir
Date: Fri Nov 30 2018 - 01:24:32 EST
+Paul, +Eddie and +Feng.
Hi Steven, any update regarding this patch. I'm including some folks
from server performance analysis team in microsoft, they are currently
investigating early boot-up latencies using ftrace.
Abderrahmane Benbachir <abderrahmane.benbachir@xxxxxxxxxx> a ÃcritÂ:
Hi Steve,
I believe this patch is quite stable. I know some folks that were using
it to debug early VM/KVM handshak and seemed very helpful for them.
Previous changes:
PATCH v1: Initial patch
PATCH v2:
Removed arch specific code and use the default clock.
Add more code re-usability
Add HAVE_VERY_EARLY_FTRACE config option which is disabled by default
PATCH v3 starts here :
---------------------------------------------------------------------
The very early tracing will start from the beginning of start_kernel()
and will stop at ftrace_init()
start_kernel()
{
ftrace_early_init() <--- start early function tracing
...
(calls)
...
ftrace_init() <--- stop early function tracing
early_trace_init(); <--- fill ring buffer, before starting function tracer
...
}
The events are placed in a temporary buffer, which will be copied to
the trace buffer after memory setup.
Dynamic tracing is not implemented with live patching, we use
ftrace_filter and ftrace_notrace to find which functions to be
filtered (traced / not traced), then during the callback from
mcount hook, we do binary search lookup to decide which function
to be save or not.
Signed-off-by: Abderrahmane Benbachir <abderrahmane.benbachir@xxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
arch/x86/Kconfig | 1 +
arch/x86/kernel/ftrace_32.S | 45 ++++--
arch/x86/kernel/ftrace_64.S | 14 ++
include/linux/ftrace.h | 16 +-
init/main.c | 1 +
kernel/trace/Kconfig | 51 +++++++
kernel/trace/ftrace.c | 289 +++++++++++++++++++++++++++++++++++-
kernel/trace/trace.c | 3 +
8 files changed, 408 insertions(+), 12 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 1a0be022f91d..3d5b89061a51 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -148,6 +148,7 @@ config X86
select HAVE_FENTRY if X86_64 || DYNAMIC_FTRACE
select HAVE_FTRACE_MCOUNT_RECORD
select HAVE_FUNCTION_GRAPH_TRACER
+ select HAVE_VERY_EARLY_FTRACE
select HAVE_FUNCTION_TRACER
select HAVE_GCC_PLUGINS
select HAVE_HW_BREAKPOINT
diff --git a/arch/x86/kernel/ftrace_32.S b/arch/x86/kernel/ftrace_32.S
index 4c8440de3355..1f2889d9e37e 100644
--- a/arch/x86/kernel/ftrace_32.S
+++ b/arch/x86/kernel/ftrace_32.S
@@ -31,12 +31,8 @@ EXPORT_SYMBOL(mcount)
# define MCOUNT_FRAME 0 /* using frame = false */
#endif
-ENTRY(function_hook)
- ret
-END(function_hook)
-
-ENTRY(ftrace_caller)
+.macro save_mcount_regs
#ifdef USING_FRAME_POINTER
# ifdef CC_USING_FENTRY
/*
@@ -73,11 +69,9 @@ ENTRY(ftrace_caller)
movl function_trace_op, %ecx
subl $MCOUNT_INSN_SIZE, %eax
+ .endm
-.globl ftrace_call
-ftrace_call:
- call ftrace_stub
-
+.macro restore_mcount_regs
addl $4, %esp /* skip NULL pointer */
popl %edx
popl %ecx
@@ -90,6 +84,39 @@ ftrace_call:
addl $4, %esp /* skip parent ip */
# endif
#endif
+ .endm
+
+ENTRY(function_hook)
+#ifdef CONFIG_VERY_EARLY_FUNCTION_TRACER
+ cmpl $__PAGE_OFFSET, %esp
+ jb vearly_stub /* Paging not enabled yet? */
+
+ cmpl $ftrace_stub, ftrace_vearly_trace_function
+ jnz vearly_trace
+
+vearly_stub:
+ ret
+
+vearly_trace:
+ save_mcount_regs
+ call *ftrace_vearly_trace_function
+ restore_mcount_regs
+
+ jmp vearly_stub
+#else
+ ret
+#endif
+END(function_hook)
+
+ENTRY(ftrace_caller)
+ save_mcount_regs
+
+.globl ftrace_call
+ftrace_call:
+ call ftrace_stub
+
+ restore_mcount_regs
+
.Lftrace_ret:
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
.globl ftrace_graph_call
diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
index 91b2cff4b79a..879db2c759e3 100644
--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -151,7 +151,21 @@ EXPORT_SYMBOL(mcount)
#ifdef CONFIG_DYNAMIC_FTRACE
ENTRY(function_hook)
+#ifdef CONFIG_VERY_EARLY_FUNCTION_TRACER
+ cmpq $ftrace_stub, ftrace_vearly_trace_function
+ jnz vearly_trace
+
+vearly_stub:
retq
+
+vearly_trace:
+ save_mcount_regs
+ call *ftrace_vearly_trace_function
+ restore_mcount_regs
+ jmp vearly_stub
+#else
+ retq
+#endif
ENDPROC(function_hook)
ENTRY(ftrace_caller)
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index a397907e8d72..78e023c61289 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -239,6 +239,16 @@ static inline void ftrace_free_init_mem(void) { }
static inline void ftrace_free_mem(struct module *mod, void *start,
void *end) { }
#endif /* CONFIG_FUNCTION_TRACER */
+#ifdef CONFIG_VERY_EARLY_FUNCTION_TRACER
+extern void ftrace_early_init(char *command_line);
+extern void ftrace_early_shutdown(void);
+extern void ftrace_early_fill_ringbuffer(void *data);
+#else
+static inline void ftrace_early_init(char *command_line) { }
+static inline void ftrace_early_shutdown(void) { }
+static inline void ftrace_early_fill_ringbuffer(void *data) { }
+#endif
+
#ifdef CONFIG_STACK_TRACER
#define STACK_TRACE_ENTRIES 500
@@ -443,6 +453,10 @@ unsigned long ftrace_get_addr_curr(struct
dyn_ftrace *rec);
extern ftrace_func_t ftrace_trace_function;
+#if defined(CONFIG_VERY_EARLY_FUNCTION_TRACER) &&
defined(CONFIG_DYNAMIC_FTRACE)
+extern ftrace_func_t ftrace_vearly_trace_function;
+#endif
+
int ftrace_regex_open(struct ftrace_ops *ops, int flag,
struct inode *inode, struct file *file);
ssize_t ftrace_filter_write(struct file *file, const char __user *ubuf,
@@ -716,7 +730,7 @@ static inline unsigned long get_lock_parent_ip(void)
#ifdef CONFIG_FTRACE_MCOUNT_RECORD
extern void ftrace_init(void);
#else
-static inline void ftrace_init(void) { }
+static inline void ftrace_init(void) { ftrace_early_shutdown(); }
#endif
/*
diff --git a/init/main.c b/init/main.c
index 18f8f0140fa0..1b289325223f 100644
--- a/init/main.c
+++ b/init/main.c
@@ -533,6 +533,7 @@ asmlinkage __visible void __init start_kernel(void)
char *command_line;
char *after_dashes;
+ ftrace_early_init(boot_command_line);
set_task_stack_end_magic(&init_task);
smp_setup_processor_id();
debug_objects_early_init();
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 5e3de28c7677..4b358bf6abb0 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -19,6 +19,11 @@ config HAVE_FUNCTION_TRACER
help
See Documentation/trace/ftrace-design.rst
+config HAVE_VERY_EARLY_FTRACE
+ bool
+ help
+ See Documentation/trace/ftrace-design.txt
+
config HAVE_FUNCTION_GRAPH_TRACER
bool
help
@@ -155,6 +160,52 @@ config FUNCTION_TRACER
(the bootup default), then the overhead of the instructions is very
small and not measurable even in micro-benchmarks.
+config VERY_EARLY_FUNCTION_TRACER
+ bool "Very Early Kernel Function Tracer"
+ depends on FUNCTION_TRACER
+ depends on HAVE_VERY_EARLY_FTRACE
+ help
+ Normally, function tracing can only start after memory has been
+ initialized early in boot. If "ftrace=function" is added to the
+ command line, then function tracing will start after memory setup.
+ In order to trace functions before that, this option will
+ have function tracing starts before memory setup is complete, by
+ placing the trace in a temporary buffer, which will be copied to
+ the trace buffer after memory setup. The size of this temporary
+ buffer is defined by VERY_EARLY_FTRACE_BUF_SHIFT.
+
+config VERY_EARLY_FTRACE_BUF_SHIFT
+ int "Temporary buffer size (17 => 128 KB, 24 => 16 MB)"
+ depends on VERY_EARLY_FUNCTION_TRACER
+ range 8 24
+ default 19
+ help
+ Select the size of the buffer to be used for storing function calls at
+ very early stage.
+ The value defines the size as a power of 2.
+ Examples:
+ 20 => 1 MB
+ 19 => 512 KB
+ 17 => 128 KB
+
+config VERY_EARLY_FTRACE_FILTER_SHIFT
+ int "Temporary filter size (filter/notrace) (17 => 128 KB, 19 => 512 KB)"
+ depends on VERY_EARLY_FUNCTION_TRACER
+ depends on FTRACE_MCOUNT_RECORD
+ range 0 19
+ default 17
+ help
+ Select the size of the filter buffer to be used for filtering (trace/
+ no trace) functions at very early stage.
+ Two buffers (trace/no_trace) will be created using by this option.
+ These following kernel parameters control filtering during bootup :
+ "ftrace_filter", "ftrace_notrace".
+ The value defines the size as a power of 2.
+ Examples:
+ 19 => 512 KB for each buffer
+ 18 => 256 KB for each buffer
+ 17 => 128 KB for each buffer
+
config FUNCTION_GRAPH_TRACER
bool "Kernel Function Graph Tracer"
depends on HAVE_FUNCTION_GRAPH_TRACER
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index f536f601bd46..45d575ae2056 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -65,6 +65,11 @@
#define FTRACE_HASH_DEFAULT_BITS 10
#define FTRACE_HASH_MAX_BITS 12
+#ifdef CONFIG_FTRACE_MCOUNT_RECORD
+extern unsigned long __start_mcount_loc[];
+extern unsigned long __stop_mcount_loc[];
+#endif
+
#ifdef CONFIG_DYNAMIC_FTRACE
#define INIT_OPS_HASH(opsname) \
.func_hash = &opsname.local_hash, \
@@ -6126,11 +6131,11 @@ void __init ftrace_free_init_mem(void)
void __init ftrace_init(void)
{
- extern unsigned long __start_mcount_loc[];
- extern unsigned long __stop_mcount_loc[];
unsigned long count, flags;
int ret;
+ ftrace_early_shutdown();
+
local_irq_save(flags);
ret = ftrace_dyn_arch_init();
local_irq_restore(flags);
@@ -7092,3 +7097,283 @@ void ftrace_graph_exit_task(struct task_struct *t)
kfree(ret_stack);
}
#endif
+
+
+#ifdef CONFIG_VERY_EARLY_FUNCTION_TRACER
+
+#define VEARLY_BUFF_LEN ((1 << CONFIG_VERY_EARLY_FTRACE_BUF_SHIFT) / \
+ sizeof(struct ftrace_vearly_entry))
+
+struct ftrace_vearly_entry {
+ unsigned long ip;
+ unsigned long parent_ip;
+ unsigned long long clock;
+};
+/*
+ * Only CPU0 is running in early stage, no need to have per-cpu buffer
+ */
+static struct ftrace_vearly_entry
ftrace_vearly_entries[VEARLY_BUFF_LEN] __initdata;
+static const unsigned long VEARLY_BUFF_MAX __initconst = VEARLY_BUFF_LEN;
+static unsigned long vearly_entries_count __initdata;
+static char tmp_cmdline[COMMAND_LINE_SIZE] __initdata;
+
+
+#ifdef CONFIG_DYNAMIC_FTRACE
+ftrace_func_t ftrace_vearly_trace_function __read_mostly = ftrace_stub;
+#else
+# define ftrace_vearly_trace_function ftrace_trace_function
+#endif
+
+static inline __init void ftrace_vearly_disable(void)
+{
+ ftrace_vearly_trace_function = ftrace_stub;
+}
+
+#ifdef CONFIG_FTRACE_MCOUNT_RECORD
+#define VEARLY_FILTER_LEN ((1 << CONFIG_VERY_EARLY_FTRACE_FILTER_SHIFT) / \
+ sizeof(unsigned long))
+struct ftrace_vearly_filtering {
+ unsigned long list[VEARLY_FILTER_LEN];
+ char buf[COMMAND_LINE_SIZE];
+ int size;
+};
+static const unsigned long VEARLY_FILTER_MAX __initconst =
VEARLY_FILTER_LEN;
+static struct ftrace_vearly_filtering ftrace_data_notrace __initdata;
+static struct ftrace_vearly_filtering ftrace_data_filter __initdata;
+
+static __init int ftrace_vearly_filter_has_addr(unsigned long addr,
+ unsigned long *filter, int *size)
+{
+ int i;
+
+ for (i = 0; i < *size; i++) {
+ if (filter[i] == addr)
+ return 1;
+ }
+ return 0;
+}
+
+static __init int
+ftrace_vearly_match_record(unsigned long ip, struct ftrace_glob *func_g)
+{
+ char str[KSYM_SYMBOL_LEN];
+ char *modname;
+
+ kallsyms_lookup(ip, NULL, NULL, &modname, str);
+ return ftrace_match(str, func_g);
+}
+
+static __init void
+ftrace_vearly_regex(char *func, unsigned long *filter, int *size)
+{
+ struct ftrace_glob func_g = { .type = MATCH_FULL };
+ unsigned long *start = __start_mcount_loc;
+ unsigned long *end = __stop_mcount_loc;
+ unsigned long count;
+ unsigned long addr;
+ unsigned long *p;
+ int clear_filter = 0;
+
+ count = end - start;
+
+ if (!count)
+ return;
+
+ if (func) {
+ func_g.type = filter_parse_regex(func, strlen(func), &func_g.search,
+ &clear_filter);
+ func_g.len = strlen(func_g.search);
+ }
+
+ p = start;
+ while (p < end) {
+ addr = ftrace_call_adjust(*p++);
+ if (!addr)
+ continue;
+
+ if ((*size) > VEARLY_FILTER_MAX)
+ return;
+
+ if (ftrace_vearly_match_record(addr, &func_g)) {
+ if (!ftrace_vearly_filter_has_addr(addr, filter, size))
+ filter[(*size)++] = addr;
+ }
+ }
+}
+
+static int __init ftrace_addr_compare(const void *a, const void *b)
+{
+ if (*(unsigned long *)a > *(unsigned long *)b)
+ return 1;
+ if (*(unsigned long *)a < *(unsigned long *)b)
+ return -1;
+
+ return 0;
+}
+
+static void __init ftrace_addr_swap(void *a, void *b, int size)
+{
+ unsigned long t = *(unsigned long *)a;
+ *(unsigned long *)a = *(unsigned long *)b;
+ *(unsigned long *)b = t;
+}
+
+static __init int set_ftrace_vearly_filtering(void *data, char *str)
+{
+ struct ftrace_vearly_filtering *ftrace_data = data;
+ char *func;
+ char *buf;
+
+ if (!ftrace_data)
+ return 0;
+ buf = ftrace_data->buf;
+ strlcpy(buf, str, COMMAND_LINE_SIZE);
+
+ while (buf) {
+ func = strsep(&buf, ",");
+ ftrace_vearly_regex(func, ftrace_data->list, &ftrace_data->size);
+ }
+ /* sort filter to use binary search on it */
+ sort(ftrace_data->list, ftrace_data->size,
+ sizeof(unsigned long), ftrace_addr_compare, ftrace_addr_swap);
+
+ return 1;
+}
+
+#define ftrace_vearly_bsearch_addr(addr, data) bsearch(&addr, data.list,\
+ data.size, sizeof(unsigned long), ftrace_addr_compare)
+
+#endif /* CONFIG_FTRACE_MCOUNT_RECORD */
+
+
+static __init void
+ftrace_function_vearly_trace_call(unsigned long ip, unsigned long parent_ip,
+ struct ftrace_ops *op, struct pt_regs *regs)
+{
+ struct ftrace_vearly_entry *entry;
+
+#ifdef CONFIG_FTRACE_MCOUNT_RECORD
+ if (ftrace_data_notrace.size &&
+ ftrace_vearly_bsearch_addr(ip, ftrace_data_notrace))
+ return;
+
+ if (ftrace_data_filter.size &&
+ !ftrace_vearly_bsearch_addr(ip, ftrace_data_filter))
+ return;
+#endif
+
+ if (vearly_entries_count >= VEARLY_BUFF_MAX) {
+ /* stop tracing when buffer is full */
+ ftrace_vearly_disable();
+ return;
+ }
+
+ entry = &ftrace_vearly_entries[vearly_entries_count++];
+ entry->ip = ip;
+ entry->parent_ip = parent_ip;
+ entry->clock = trace_clock_local();
+}
+
+/*
+ * Will be passed to ringbuffer by early_trace_clock
+ */
+static u64 early_timestamp __initdata;
+
+static __init u64 early_trace_clock(void)
+{
+ return early_timestamp;
+}
+
+void __init ftrace_early_fill_ringbuffer(void *data)
+{
+ struct ftrace_vearly_entry *entry;
+ struct trace_array *tr = data;
+ int i;
+
+ if (ftrace_vearly_entries <= 0)
+ return;
+
+ ring_buffer_set_clock(tr->trace_buffer.buffer, early_trace_clock);
+ preempt_disable_notrace();
+ for (i = 0; i < vearly_entries_count; i++) {
+ entry = &ftrace_vearly_entries[i];
+ early_timestamp = entry->clock;
+ trace_function(tr, entry->ip, entry->parent_ip, 0, 0);
+ }
+ preempt_enable_notrace();
+ ring_buffer_set_clock(tr->trace_buffer.buffer, trace_clock_local);
+}
+
+/*
+ * this will be used as __setup_param
+ */
+struct ftrace_vearly_obs_param {
+ int (*setup_func)(void *, char*);
+ const char *str;
+ void *data;
+};
+static struct ftrace_vearly_obs_param ftrace_vearly_params[] __initdata = {
+#ifdef CONFIG_FTRACE_MCOUNT_RECORD
+ {
+ .str = "ftrace_notrace",
+ .data = &ftrace_data_notrace,
+ .setup_func = set_ftrace_vearly_filtering,
+ },
+ {
+ .str = "ftrace_filter",
+ .data = &ftrace_data_filter,
+ .setup_func = set_ftrace_vearly_filtering,
+ },
+#endif
+};
+
+static int __init ftrace_do_very_early_param(char *param, char *val,
+ const char *unused, void *arg)
+{
+ int size = ARRAY_SIZE(ftrace_vearly_params);
+ struct ftrace_vearly_obs_param *p;
+ int i;
+
+ for (i = 0; i < size; i++) {
+ p = &ftrace_vearly_params[i];
+ if (strcmp(param, p->str) == 0) {
+ p->setup_func(p->data, val);
+ return 0;
+ }
+ }
+ return 0;
+}
+
+void __init ftrace_early_init(char *command_line)
+{
+ /* proceed only if function tracing was enabled */
+ if (!strstr(command_line, "ftrace=function "))
+ return;
+
+ strlcpy(tmp_cmdline, command_line, COMMAND_LINE_SIZE);
+ parse_args("ftrace vearly options", tmp_cmdline, NULL, 0, 0, 0, NULL,
+ ftrace_do_very_early_param);
+
+ // After this point, we enable early function tracing
+ ftrace_vearly_trace_function = ftrace_function_vearly_trace_call;
+}
+
+void __init ftrace_early_shutdown(void)
+{
+ if (ftrace_vearly_trace_function == ftrace_stub)
+ return;
+
+ // Disable early tracing
+ ftrace_vearly_disable();
+
+#ifdef CONFIG_FTRACE_MCOUNT_RECORD
+ pr_info("ftrace: vearly %lu entries, notrace=%d, filter=%d",
+ vearly_entries_count,
+ ftrace_data_notrace.size,
+ ftrace_data_filter.size);
+#else
+ pr_info("ftrace: vearly %lu recorded entries", vearly_entries_count);
+#endif
+}
+
+#endif /* CONFIG_VERY_EARLY_FUNCTION_TRACER */
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index bf6f1d70484d..08763c380a3e 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -8551,6 +8551,9 @@ __init static int tracer_alloc_buffers(void)
/* Function tracing may start here (via kernel command line) */
init_function_trace();
+ /* Pre-fill the ring buffer with very early events */
+ ftrace_early_fill_ringbuffer(&global_trace);
+
/* All seems OK, enable tracing */
tracing_disabled = 0;
--
2.17.1