On Wed, 5 Dec 2018 at 10:54, Will Deacon <[email protected]> wrote: > > Hi Anders, Steve, > > On Tue, Dec 04, 2018 at 08:29:03PM +0100, Anders Roxell 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..7080eb464983 100644 > > --- a/kernel/trace/ftrace.c > > +++ b/kernel/trace/ftrace.c > > @@ -2419,11 +2419,19 @@ void __weak ftrace_replace_code(int enable) > > { > > struct dyn_ftrace *rec; > > struct ftrace_page *pg; > > + bool schedulable; > > int failed; > > > > if (unlikely(ftrace_disabled)) > > return; > > > > + /* > > + * Some archs calls this function with interrupts or preemption > > + * disabled. However, for other archs that can preempt, this can cause > > + * an tremendous unneeded latency. > > + */ > > + schedulable = !irqs_disabled() && !preempt_count(); > > Is there a reason not to use preemptible() here?
As I understand it preemptible() is defined to 0 if CONFIG_PREEMPT_COUNT is disabled. Thats no good right ? Cheers, Anders
