| Message ID | 1464779939-24986-3-git-send-email-zhang.chunyan@linaro.org |
|---|---|
| State | New |
| Headers | show |
On Tue, Jun 7, 2016 at 6:04 PM, Alexander Shishkin <alexander.shishkin@linux.intel.com> wrote: > Chunyan Zhang <zhang.chunyan@linaro.org> 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. From what I understand, we have no way to log as much information as Ftrace has done if we want to control the overhead of writing STM in a limited/acceptable range. Exporting information to STM is much more time-consuming than writing ring buffer, the thought was simply that export as much useful information as possible while taking a limited bytes. Thanks, Chunyan > >> +#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? > >> + >> +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
diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile index 979e7bf..445afa8 100644 --- a/kernel/trace/Makefile +++ b/kernel/trace/Makefile @@ -69,4 +69,5 @@ obj-$(CONFIG_UPROBE_EVENT) += trace_uprobe.o obj-$(CONFIG_TRACEPOINT_BENCHMARK) += trace_benchmark.o +obj-$(CONFIG_STM_FTRACE) += trace_output_stm.o libftrace-y := ftrace.o diff --git a/kernel/trace/trace_output_stm.c b/kernel/trace/trace_output_stm.c new file mode 100644 index 0000000..f6a3c01 --- /dev/null +++ b/kernel/trace/trace_output_stm.c @@ -0,0 +1,27 @@ +/* + * Output interface from Ftrace to STM buffer + * Copyright (c) 2016, Linaro Ltd. + * + * This program is free software; you can redistribute it and/or modify it + * under the terms and conditions of the GNU General Public License, + * version 2, as published by the Free Software Foundation. + * + * This program is distributed in the hope it will be useful, but WITHOUT + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for + * more details. + */ + +#include "trace_output_stm.h" + +/* Offset above the start channel number */ +#define STM_FTRACE_CHAN 0 + +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 */
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]. [1] http://thread.gmane.org/gmane.linux.kernel/1114274/focus=1114275 Signed-off-by: Chunyan Zhang <zhang.chunyan@linaro.org> --- kernel/trace/Makefile | 1 + kernel/trace/trace_output_stm.c | 27 +++++++++++++++++++++++++++ kernel/trace/trace_output_stm.h | 14 ++++++++++++++ 3 files changed, 42 insertions(+) create mode 100644 kernel/trace/trace_output_stm.c create mode 100644 kernel/trace/trace_output_stm.h -- 1.9.1