Messages in this thread | | | Date | Fri, 2 Jan 2009 20:40:14 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] tracing/function-graph-tracer: tracing only syscalls mode |
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* Frederic Weisbecker <fweisbec@gmail.com> wrote:
> Impact: make more easy the syscalls tracing > > This patch extends to syscalls the features which let one to trace > only one ore more function (and those they call). > This way we can get rid of the workqueues, kernel threads, softirqs from > ksoftirqd and only have the syscall path on the trace. > > Note that hardirq that interrupt the syscalls are still traced. But we could > add an option to disable the interrupt tracing as well in the future. > > To use this new feature: > > echo function_graph > /debugfs/tracing/current_tracer > echo syscalls > /debugfs/tracing/set_graph_function
nice. I think a key item is missing though:
> @@ -1397,6 +1398,9 @@ asmregparm long syscall_trace_enter(struct pt_regs *regs) > { > long ret = 0; > > + /* Tell the function graph tracer we are entering a system call */ > + ftrace_graph_syscall_enter();
We could actually trace the _syscalls_ themselves, a'la strace:
munmap(0xb7ff3000, 4096) = 0
So instead of the current ftrace output:
0) cc1-30212 | | sys32_mmap2() { 0) cc1-30212 | | down_write() { 0) cc1-30212 | 0.272 us | _spin_lock_irq(); 0) cc1-30212 | 0.969 us | } 0) cc1-30212 | | do_mmap_pgoff() {
We could get something like:
0) cc1-30212 | | sys32_mmap2(0xb7ff3000, 4096) { 0) cc1-30212 | | down_write() { 0) cc1-30212 | 0.272 us | _spin_lock_irq(); 0) cc1-30212 | 0.969 us | } 0) cc1-30212 | | do_mmap_pgoff() { [...] 0) cc1-30212 | + 22.537 us | } = 0
Or maybe as separate trace entries:
0) cc1-30212 | |> sys32_mmap2 [0xb7ff3000, 4096] 0) cc1-30212 | | sys32_mmap2 { 0) cc1-30212 | | down_write() { 0) cc1-30212 | 0.272 us | _spin_lock_irq(); 0) cc1-30212 | 0.969 us | } 0) cc1-30212 | | do_mmap_pgoff() { [...] 0) cc1-30212 | + 22.537 us | } 0) cc1-30212 | |< sys32_mmap2 => 0
For that we'd have to pass in something like the syscall function address (sys_call_table[regs->ax]), and the up to 6 parameters [regs->bx,cx,dx,si,di,bp].
(and initially we could just print all of them i guess, instead of a variable-width thing)
We wouldnt do smart decoding of syscall arguments normally - just print the raw arguments with no decoding. (like strace -e raw=all)
How does this sound?
Ingo
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