[RFC PATCH 2/4] trace: Introduce an output interface from ftrace to STM
From: alexander.shishkin@linux.intel.com (Alexander Shishkin)
Date: 2016-06-07 10:04:47
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lkml
Chunyan Zhang [off-list ref] writes:
This patch is introducing a new function to print Ftrace messages to STM buffer when the traces happen. In order to reduce the effect on timing overhead as much as possible, only the current function and its parent ip address will be recorded into STM in this patch. This idea was first introduced by Philippe Langlais at ST-Microelectronics a long time ago[1].
So why is this useful? The value of trace points is in their payload.
+#define STM_FTRACE_CHAN 0
This is why we have the stm master/channel allocation policy, which should already assign a channel to your stm_source device when it is linked to an stm device. Also, why is this a separate compilation unit from the stm_ftrace.o?
quoted hunk ↗ jump to hunk
+ +void ftrace_stm_func(unsigned long ip, unsigned long parent_ip) +{ + unsigned long ip_array[2] = {ip, parent_ip}; + + stm_ftrace_write((char *)ip_array, sizeof(unsigned long) * 2, + STM_FTRACE_CHAN); +} +EXPORT_SYMBOL_GPL(ftrace_stm_func);diff --git a/kernel/trace/trace_output_stm.h b/kernel/trace/trace_output_stm.h new file mode 100644 index 0000000..fc3f989 --- /dev/null +++ b/kernel/trace/trace_output_stm.h@@ -0,0 +1,14 @@ +#ifndef __TRACE_OUTPUT_STM_H +#define __TRACE_OUTPUT_STM_H + +#include <linux/module.h> + +#ifdef CONFIG_STM_FTRACE +extern void stm_ftrace_write(const char *buf, unsigned int len, + unsigned int chan); +extern void ftrace_stm_func(unsigned long ip, unsigned long parent_ip); +#else +static inline void ftrace_stm_func(unsigned long ip, unsigned long parent_ip) {} +#endif + +#endif /* __TRACE_OUTPUT_STM_H */-- 1.9.1