| Message ID | 20181204192903.8193-1-anders.roxell@linaro.org |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v2] tracing: add cond_resched to ftrace_replace_code() | expand |
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) <rostedt@goodmis.org> > Signed-off-by: Anders Roxell <anders.roxell@linaro.org> > --- > 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? Will
On Wed, 5 Dec 2018 at 10:54, Will Deacon <will.deacon@arm.com> 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) <rostedt@goodmis.org> > > Signed-off-by: Anders Roxell <anders.roxell@linaro.org> > > --- > > 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
On Wed, 5 Dec 2018 11:43:12 +0100 Anders Roxell <anders.roxell@linaro.org> wrote: > > > + 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 ? No it's not, which means this isn't a good approach. I have a much better idea on how to solve this. I'll post a small patch set in a bit. -- Steve
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(); + do_for_each_ftrace_rec(pg, rec) { if (rec->flags & FTRACE_FL_DISABLED) @@ -2435,6 +2443,8 @@ void __weak ftrace_replace_code(int enable) /* Stop processing */ return; } + if (schedulable) + cond_resched(); } while_for_each_ftrace_rec(); }
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) <rostedt@goodmis.org> Signed-off-by: Anders Roxell <anders.roxell@linaro.org> --- kernel/trace/ftrace.c | 10 ++++++++++ 1 file changed, 10 insertions(+) -- 2.19.2