| Message ID | 1482360288-124624-1-git-send-email-joelaf@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, Dec 21, 2016 at 02:44:46PM -0800, Joel Fernandes wrote: > Function graph tracer shows negative time (wrap around) when tracing > __switch_to if the nosleep-time trace option is enabled. > > Time compensation for nosleep-time is done by an ftrace probe on > sched_switch. This doesn't work well for the following events (with > letters representing timestamps): > A - sched switch probe called for task T switch out > B - __switch_to calltime is recorded > C - sched_switch probe called for task T switch in > D - __switch_to rettime is recorded > > If C - A > D - B, then we end up over compensating for the time spent in > __switch_to giving rise to negative times in the trace output. > > On x86, __switch_to is not traced if function graph tracer is enabled. > Do the same for arm64 as well. > > Cc: Todd Kjos <tkjos@google.com> > Cc: Steven Rostedt <rostedt@goodmis.org> > Cc: Will Deacon <will.deacon@arm.com> > Cc: Mark Rutland <mark.rutland@arm.com> > Signed-off-by: Joel Fernandes <joelaf@google.com> > --- > arch/arm64/kernel/process.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) Thanks, queued for 4.11. Will
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index 01753cd..e84ee27 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -324,7 +324,7 @@ void uao_thread_switch(struct task_struct *next) /* * Thread switching. */ -struct task_struct *__switch_to(struct task_struct *prev, +__notrace_funcgraph struct task_struct *__switch_to(struct task_struct *prev, struct task_struct *next) { struct task_struct *last;
Function graph tracer shows negative time (wrap around) when tracing __switch_to if the nosleep-time trace option is enabled. Time compensation for nosleep-time is done by an ftrace probe on sched_switch. This doesn't work well for the following events (with letters representing timestamps): A - sched switch probe called for task T switch out B - __switch_to calltime is recorded C - sched_switch probe called for task T switch in D - __switch_to rettime is recorded If C - A > D - B, then we end up over compensating for the time spent in __switch_to giving rise to negative times in the trace output. On x86, __switch_to is not traced if function graph tracer is enabled. Do the same for arm64 as well. Cc: Todd Kjos <tkjos@google.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Will Deacon <will.deacon@arm.com> Cc: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Joel Fernandes <joelaf@google.com> --- arch/arm64/kernel/process.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)