Since the kprobes itself owns a hash table to get a kprobe
data structure corresponding to the given ip address, there
is no need to test ftrace hash in ftrace side.
To achive better performance on ftrace-based kprobe,
FTRACE_OPS_FL_SELF_FILTER flag to ftrace_ops which means
that ftrace skips testing its own hash table.
Without this patch, ftrace_lookup_ip() is biggest cycles
consumer when 20,000 kprobes are enabled.
----
Samples: 1K of event 'cycles', Event count (approx.): 340068894
+ 20.77% [k] ftrace_lookup_ip
+ 8.33% [k] kprobe_trace_func
+ 4.83% [k] get_kprobe_cached
----
With this patch, ftrace_lookup_ip() vanished from the
cycles consumer list (of course, there is no caller on
hotpath anymore :))
----
Samples: 1K of event 'cycles', Event count (approx.): 186861492
+ 9.95% [k] kprobe_trace_func
+ 6.00% [k] kprobe_ftrace_handler
+ 5.53% [k] get_kprobe_cached
----
Changes from v10:
- Update comment of the flag according to Steven's comment.
Changes from v7:
- Re-evaluate the performance improvement.
Signed-off-by: Masami Hiramatsu <masami.hiramatsu...@hitachi.com>
Cc: Steven Rostedt <rost...@goodmis.org>
Cc: Frederic Weisbecker <fweis...@gmail.com>
Cc: Ingo Molnar <mi...@redhat.com>
---
include/linux/ftrace.h | 3 +++
kernel/kprobes.c | 2 +-
kernel/trace/ftrace.c | 3 ++-
3 files changed, 6 insertions(+), 2 deletions(-)
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index ae9504b..5653001 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -93,6 +93,8 @@ typedef void (*ftrace_func_t)(unsigned long ip, unsigned long
parent_ip,
* INITIALIZED - The ftrace_ops has already been initialized (first use time
* register_ftrace_function() is called, it will initialized the
ops)
* DELETED - The ops are being deleted, do not let them be registered again.
+ * SELF_FILTER - The ftrace_ops function has its own ip filter and does not
+ * need to rely on the ftrace internal ip filtering.
*/
enum {
FTRACE_OPS_FL_ENABLED = 1 << 0,
@@ -105,6 +107,7 @@ enum {
FTRACE_OPS_FL_STUB = 1 << 7,
FTRACE_OPS_FL_INITIALIZED = 1 << 8,
FTRACE_OPS_FL_DELETED = 1 << 9,
+ FTRACE_OPS_FL_SELF_FILTER = 1 << 10,
};
/*
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index f0ea46c..4f1a72d 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1037,7 +1037,7 @@ static struct kprobe *alloc_aggr_kprobe(struct kprobe *p)
#ifdef CONFIG_KPROBES_ON_FTRACE
static struct ftrace_ops kprobe_ftrace_ops __read_mostly = {
.func = kprobe_ftrace_handler,
- .flags = FTRACE_OPS_FL_SAVE_REGS,
+ .flags = FTRACE_OPS_FL_SAVE_REGS | FTRACE_OPS_FL_SELF_FILTER,
};
static int kprobe_ftrace_enabled;
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 4a54a25..062ca20 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -4501,7 +4501,8 @@ __ftrace_ops_list_func(unsigned long ip, unsigned long
parent_ip,
*/
preempt_disable_notrace();
do_for_each_ftrace_op(op, ftrace_ops_list) {
- if (ftrace_ops_test(op, ip, regs))
+ if (op->flags & FTRACE_OPS_FL_SELF_FILTER ||
+ ftrace_ops_test(op, ip, regs))
op->func(ip, parent_ip, op, regs);
} while_for_each_ftrace_op(op);
preempt_enable_notrace();
--
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