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authorSteven Rostedt <srostedt@redhat.com>2011-09-22 20:01:55 +0200
committerSteven Rostedt <rostedt@goodmis.org>2012-04-24 03:15:55 +0200
commit07d777fe8c3985bc83428c2866713c2d1b3d4129 (patch)
treef14c6aa59b9719761ad9feebebca22550ebdf0e3 /kernel/trace/trace.h
parentMerge tag 'v3.4-rc2' into perf/core (diff)
downloadlinux-07d777fe8c3985bc83428c2866713c2d1b3d4129.tar.xz
linux-07d777fe8c3985bc83428c2866713c2d1b3d4129.zip
tracing: Add percpu buffers for trace_printk()
Currently, trace_printk() uses a single buffer to write into to calculate the size and format needed to save the trace. To do this safely in an SMP environment, a spin_lock() is taken to only allow one writer at a time to the buffer. But this could also affect what is being traced, and add synchronization that would not be there otherwise. Ideally, using percpu buffers would be useful, but since trace_printk() is only used in development, having per cpu buffers for something never used is a waste of space. Thus, the use of the trace_bprintk() format section is changed to be used for static fmts as well as dynamic ones. Then at boot up, we can check if the section that holds the trace_printk formats is non-empty, and if it does contain something, then we know a trace_printk() has been added to the kernel. At this time the trace_printk per cpu buffers are allocated. A check is also done at module load time in case a module is added that contains a trace_printk(). Once the buffers are allocated, they are never freed. If you use a trace_printk() then you should know what you are doing. A buffer is made for each type of context: normal softirq irq nmi The context is checked and the appropriate buffer is used. This allows for totally lockless usage of trace_printk(), and they no longer even disable interrupts. Requested-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'kernel/trace/trace.h')
-rw-r--r--kernel/trace/trace.h2
1 files changed, 2 insertions, 0 deletions
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 95059f091a24..f9d85504f04b 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -826,6 +826,8 @@ extern struct list_head ftrace_events;
extern const char *__start___trace_bprintk_fmt[];
extern const char *__stop___trace_bprintk_fmt[];
+void trace_printk_init_buffers(void);
+
#undef FTRACE_ENTRY
#define FTRACE_ENTRY(call, struct_name, id, tstruct, print, filter) \
extern struct ftrace_event_call \