From: "Steven Rostedt (VMware)" <rost...@goodmis.org>
Currently trace_handle_return() looks like this:
static inline enum print_line_t trace_handle_return(struct trace_seq *s)
{
return trace_seq_has_overflowed(s) ?
TRACE_TYPE_PARTIAL_LINE : TRACE_TYPE_HANDLED;
}
Where trace_seq_overflowed(s) is:
static inline bool trace_seq_has_overflowed(struct trace_seq *s)
{
return s->full || seq_buf_has_overflowed(&s->seq);
}
And seq_buf_has_overflowed(&s->seq) is:
static inline bool
seq_buf_has_overflowed(struct seq_buf *s)
{
return s->len > s->size;
}
Making trace_handle_return() into:
return (s->full || (s->seq->len > s->seq->size)) ?
TRACE_TYPE_PARTIAL_LINE :
TRACE_TYPE_HANDLED;
One would think this is not an issue to keep as an inline. But because this
is used in the TRACE_EVENT() macro, it is extended for every tracepoint in
the system. Taking a look at a single tracepoint x86_irq_vector (was the
first one I randomly chosen). As trace_handle_return is used in the
TRACE_EVENT() macro of trace_raw_output_##call() we disassemble
trace_raw_output_x86_irq_vector and do a diff:
- is the original
+ is the out-of-line code
I removed identical lines that were different just due to different
addresses.
--- /tmp/irq-vec-orig 2017-03-16 09:12:48.569384851 -0400
+++ /tmp/irq-vec-ool 2017-03-16 09:13:39.378153385 -0400
@@ -6,27 +6,23 @@
53 push %rbx
48 89 fb mov %rdi,%rbx
4c 8b a7 c0 20 00 00 mov 0x20c0(%rdi),%r12
e8 f7 72 13 00 callq ffffffff81155c80 <trace_raw_output_prep>
83 f8 01 cmp $0x1,%eax
74 05 je ffffffff8101e993
<trace_raw_output_x86_irq_vector+0x23>
5b pop %rbx
41 5c pop %r12
5d pop %rbp
c3 retq
41 8b 54 24 08 mov 0x8(%r12),%edx
- 48 8d bb 98 10 00 00 lea 0x1098(%rbx),%rdi
+ 48 81 c3 98 10 00 00 add $0x1098,%rbx
- 48 c7 c6 7b 8a a0 81 mov $0xffffffff81a08a7b,%rsi
+ 48 c7 c6 ab 8a a0 81 mov $0xffffffff81a08aab,%rsi
- e8 c5 85 13 00 callq ffffffff81156f70 <trace_seq_printf>
=== here's the start of the main difference ===
+ 48 89 df mov %rbx,%rdi
+ e8 62 7e 13 00 callq ffffffff81156810 <trace_seq_printf>
- 8b 93 b8 20 00 00 mov 0x20b8(%rbx),%edx
- 31 c0 xor %eax,%eax
- 85 d2 test %edx,%edx
- 75 11 jne ffffffff8101e9c8
<trace_raw_output_x86_irq_vector+0x58>
- 48 8b 83 a8 20 00 00 mov 0x20a8(%rbx),%rax
- 48 39 83 a0 20 00 00 cmp %rax,0x20a0(%rbx)
- 0f 93 c0 setae %al
+ 48 89 df mov %rbx,%rdi
+ e8 4a c5 12 00 callq ffffffff8114af00 <trace_handle_return>
5b pop %rbx
- 0f b6 c0 movzbl %al,%eax
=== end ===
41 5c pop %r12
5d pop %rbp
c3 retq
If you notice, the original has 22 bytes of text more than the out of line
version. As this is for every TRACE_EVENT() defined in the system, this can
become quite large.
text data bss dec hex filename
8690305 5450490 1298432 15439227 eb957b vmlinux-orig
8681725 5450490 1298432 15430647 eb73f7 vmlinux-handle
This change has a total of 8580 bytes in savings.
$ objdump -dr /tmp/vmlinux-orig | grep '^[0-9a-f]* <trace_raw_output' | wc -l
324
That's 324 tracepoints. But this does not include modules (which contain
many more tracepoints). For an allyesconfig build:
$ objdump -dr vmlinux-allyes-orig | grep '^[0-9a-f]* <trace_raw_output' | wc -l
1401
That's 1401 tracepoints giving us:
text data bss dec hex filename
137920629 140221067 53264384 331406080 13c0db00
vmlinux-allyes-orig
137827709 140221067 53264384 331313160 13bf7008
vmlinux-allyes-handle
92920 bytes in savings!!!
Link: http://lkml.kernel.org/r/20170315021431.13107-2-a...@firstfloor.org
Reported-by: Andi Kleen <a...@firstfloor.org>
Signed-off-by: Steven Rostedt (VMware) <rost...@goodmis.org>
---
include/linux/trace_events.h | 11 +----------
kernel/trace/trace.c | 12 ++++++++++++
2 files changed, 13 insertions(+), 10 deletions(-)
diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index 0af63c4381b9..a556805eff8a 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -138,16 +138,7 @@ enum print_line_t {
TRACE_TYPE_NO_CONSUME = 3 /* Handled but ask to not consume */
};
-/*
- * Several functions return TRACE_TYPE_PARTIAL_LINE if the trace_seq
- * overflowed, and TRACE_TYPE_HANDLED otherwise. This helper function
- * simplifies those functions and keeps them in sync.
- */
-static inline enum print_line_t trace_handle_return(struct trace_seq *s)
-{
- return trace_seq_has_overflowed(s) ?
- TRACE_TYPE_PARTIAL_LINE : TRACE_TYPE_HANDLED;
-}
+enum print_line_t trace_handle_return(struct trace_seq *s);
void tracing_generic_entry_update(struct trace_entry *entry,
unsigned long flags,
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 4fa8e8f3c765..b5d4b80f2d45 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1998,6 +1998,18 @@ void tracing_record_cmdline(struct task_struct *tsk)
__this_cpu_write(trace_cmdline_save, false);
}
+/*
+ * Several functions return TRACE_TYPE_PARTIAL_LINE if the trace_seq
+ * overflowed, and TRACE_TYPE_HANDLED otherwise. This helper function
+ * simplifies those functions and keeps them in sync.
+ */
+enum print_line_t trace_handle_return(struct trace_seq *s)
+{
+ return trace_seq_has_overflowed(s) ?
+ TRACE_TYPE_PARTIAL_LINE : TRACE_TYPE_HANDLED;
+}
+EXPORT_SYMBOL_GPL(trace_handle_return);
+
void
tracing_generic_entry_update(struct trace_entry *entry, unsigned long flags,
int pc)
--
2.10.2
