Messages in this thread | | | From | Donglin Peng <> | Subject | [PATCH v4 0/2] function_graph: Support recording and printing the return value of function | Date | Wed, 15 Mar 2023 06:39:09 -0700 |
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When using the function_graph tracer to analyze system call failures, it can be time-consuming to analyze the trace logs and locate the kernel function that first returns an error. This change aims to simplify the process by recording the function return value to the 'retval' member of 'ftrace_graph_ent' and printing it when outputing the trace log.
Note that even if a function's return type is void, a return value will still be printed, so it should be ignored. If you care about this, the BTF file can be used to obtain the details of function return type. We can implement a tool to process the trace log and display the return value based on its actual type.
Here is an example:
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1) | cgroup_attach_task() { 1) | cgroup_migrate_add_src() { 1) 1.403 us | cset_cgroup_from_root(); /* = 0xffff93fc86f58010 */ 1) 2.154 us | } /* cgroup_migrate_add_src = 0xffffb286c1297d00 */ 1) ! 386.538 us | cgroup_migrate_prepare_dst(); /* = 0x0 */ 1) | cgroup_migrate() { 1) 0.651 us | cgroup_migrate_add_task(); /* = 0xffff93fcfd346c00 */ 1) | cgroup_migrate_execute() { 1) | cpu_cgroup_can_attach() { 1) | cgroup_taskset_first() { 1) 0.732 us | cgroup_taskset_next(); /* = 0xffff93fc8fb20000 */ 1) 1.232 us | } /* cgroup_taskset_first = 0xffff93fc8fb20000 */ 1) 0.380 us | sched_rt_can_attach(); /* = 0x0 */ 1) 2.335 us | } /* cpu_cgroup_can_attach = -22 */ 1) 4.369 us | } /* cgroup_migrate_execute = -22 */ 1) 7.143 us | } /* cgroup_migrate = -22 */ 1) | cgroup_migrate_finish() { 1) 0.411 us | put_css_set_locked(); /* = 0x8 */ 1) + 62.397 us | put_css_set_locked(); /* = 0x80000001 */ 1) + 64.742 us | } /* cgroup_migrate_finish = 0x80000000 */ 1) ! 465.605 us | } /* cgroup_attach_task = -22 */
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After processing the above trace logs using BTF information:
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1) | cgroup_attach_task() { 1) | cgroup_migrate_add_src() { 1) 1.403 us | cset_cgroup_from_root(); /* = 0xffff93fc86f58010 */ 1) 2.154 us | } /* cgroup_migrate_add_src */ 1) ! 386.538 us | cgroup_migrate_prepare_dst(); /* = 0 */ 1) | cgroup_migrate() { 1) 0.651 us | cgroup_migrate_add_task(); 1) | cgroup_migrate_execute() { 1) | cpu_cgroup_can_attach() { 1) | cgroup_taskset_first() { 1) 0.732 us | cgroup_taskset_next(); /* = 0xffff93fc8fb20000 */ 1) 1.232 us | } /* cgroup_taskset_first = 0xffff93fc8fb20000 */ 1) 0.380 us | sched_rt_can_attach(); /* = 0 */ 1) 2.335 us | } /* cpu_cgroup_can_attach = -22 */ 1) 4.369 us | } /* cgroup_migrate_execute = -22 */ 1) 7.143 us | } /* cgroup_migrate = -22 */ 1) | cgroup_migrate_finish() { 1) 0.411 us | put_css_set_locked(); 1) + 62.397 us | put_css_set_locked(); 1) + 64.742 us | } /* cgroup_migrate_finish */ 1) ! 465.605 us | } /* cgroup_attach_task = -22 */
...
Donglin Peng (2): function_graph: Support recording and printing the return value of function tracing: Add documentation for funcgraph-retval and graph_retval_hex
Documentation/trace/ftrace.rst | 55 ++++++++++++++++ arch/arm/Kconfig | 1 + arch/arm/kernel/entry-ftrace.S | 4 ++ arch/arm64/Kconfig | 1 + arch/arm64/kernel/entry-ftrace.S | 6 +- arch/riscv/Kconfig | 1 + arch/riscv/kernel/mcount.S | 4 ++ arch/x86/Kconfig | 1 + arch/x86/kernel/ftrace_32.S | 4 ++ arch/x86/kernel/ftrace_64.S | 4 ++ include/linux/ftrace.h | 3 + kernel/trace/Kconfig | 8 +++ kernel/trace/fgraph.c | 5 +- kernel/trace/trace.h | 2 + kernel/trace/trace_entries.h | 26 ++++++++ kernel/trace/trace_functions_graph.c | 94 +++++++++++++++++++++++++--- 16 files changed, 207 insertions(+), 12 deletions(-)
-- 2.25.1
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