trace-cmd report: Print function retval in function_graph
The upstream Linux kernel has introduced a new feature, i.e.
funcgraph-retval for the function_graph tracer. (Commit ID:
a1be9ccc57f07d54278be34eed6bd679bc941c97). With this feature, the
function_graph tracer can record each function's return value along
with its execution time at the function_graph exit handler. This is
useful for debugging kernel issues, such as syscall errors.
This commit enhances 'trace-cmd report' by supporting the
function_graph retval feature if the underlying kernel supports it.
Once the feature is supported, 'trace-cmd report' will print each
function's return value in this format: '(ret=retval)" at the end
of every funcgraph leaf entry and exit event. Error codes are
printed in decimal, while others are printed in hex.
Example usage:
* Record
> trace-cmd record -p function_graph -P <pid>
The recording process is not changed: trace-cmd can communicate
with the kernel to get the actual funcgraph_exit event format.
If the kernel supports ftrace-retval, trace-cmd will use the
updated event format that has "retval" field.
* Report
> trace-cmd report -O fgraph:depth -O fgraph:tailprint
If the kernel supports this feature, the output looks like this:
<...>-1136215 [006] ..... 1724848.377495: funcgraph_entry: | __cond_resched() { (3)
<...>-1136215 [006] ..... 1724848.377495: funcgraph_entry: 0.200 us | rcu_all_qs(); (4) (ret=0x0)
<...>-1136215 [006] ..... 1724848.377496: funcgraph_exit: 0.601 us | } /* __cond_resched */ (3) (ret=0x0)
<...>-1136215 [006] ..... 1724848.377496: funcgraph_entry: 0.581 us | proc_reg_write(); (3) (ret=-5)
<...>-1136215 [006] ..... 1724848.377497: funcgraph_exit: 5.059 us | } /* vfs_write */ (2) (ret=-5)
<...>-1136215 [006] ..... 1724848.377497: funcgraph_exit: 6.332 us | } /* ksys_write */ (1) (ret=-5)
<...>-1136215 [006] ..... 1724848.377497: funcgraph_exit: + 18.414 us | } /* __x64_sys_write */ (0) (ret=-5)
Link: https://lore.kernel.org/linux-trace-devel/[email protected]
Signed-off-by: Jianfeng Wang <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>
1 file changed
