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SubjectRe: [RFC PATCH v3] ftrace: support very early function tracing

+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@polymtl.ca> a écrit :

> 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@polymtl.ca>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Cc: linux-kernel@vger.kernel.org
> ---
> 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



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