On Tue, 4 Dec 2018 20:12:28 +0100 Anders Roxell <[email protected]> wrote:
> When running in qemu on an kernel built with allmodconfig and debug > options (in particular kcov and ubsan) enabled, ftrace_replace_code > function call take minutes. The ftrace selftest calls > ftrace_replace_code to look >40000 through > ftrace_make_call/ftrace_make_nop, and these end up calling > __aarch64_insn_write/aarch64_insn_patch_text_nosync. > > Microseconds add up because this is called in a loop for each dyn_ftrace > record, and this triggers the softlockup watchdog unless we let it sleep > occasionally. > > Rework so that we call cond_resched() if !irqs_disabled() && !preempt_count(). > > Suggested-by: Steven Rostedt (VMware) <[email protected]> > Signed-off-by: Anders Roxell <[email protected]> > --- > kernel/trace/ftrace.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c > index c375e33239f7..582e3441e318 100644 > --- a/kernel/trace/ftrace.c > +++ b/kernel/trace/ftrace.c > @@ -2419,11 +2419,14 @@ void __weak ftrace_replace_code(int enable) > { > struct dyn_ftrace *rec; > struct ftrace_page *pg; > + bool schedulable; > int failed; > > if (unlikely(ftrace_disabled)) > return; > > + schedulable = !irqs_disabled() && !preempt_count(); > + > do_for_each_ftrace_rec(pg, rec) { > > if (rec->flags & FTRACE_FL_DISABLED) > @@ -2435,6 +2438,13 @@ void __weak ftrace_replace_code(int enable) > /* Stop processing */ > return; > } > + /* > + * Some archs calls this function with interrupts or preemption > + * disabled. Howeve, other archs don't and this can cause a > + * tremendous unneeded latency. > + */ Actually, could you move the comment up where schedulable gets set? Thanks! -- Steve > + if (schedulable) > + cond_resched(); > } while_for_each_ftrace_rec(); > } >
