Messages in this thread | | | Date | Thu, 8 May 2014 06:59:47 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH -tip v10 7/7] ftrace: Introduce FTRACE_OPS_FL_SELF_FILTER for ftrace-kprobe |
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On Thu, 08 May 2014 18:39:30 +0900 Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> wrote:
> Since the kprobes itself owns a hash table to get a kprobe > data structure corresponding to the given ip address, there > is no need to test ftrace hash in ftrace side. > To achive better performance on ftrace-based kprobe, > FTRACE_OPS_FL_SELF_FILTER flag to ftrace_ops which means > that ftrace skips testing its own hash table. > > Without this patch, ftrace_lookup_ip() is biggest cycles > consumer when 20,000 kprobes are enabled. > ---- > Samples: 1K of event 'cycles', Event count (approx.): 340068894 > + 20.77% [k] ftrace_lookup_ip > + 8.33% [k] kprobe_trace_func > + 4.83% [k] get_kprobe_cached > ---- > > With this patch, ftrace_lookup_ip() vanished from the > cycles consumer list (of course, there is no caller on > hotpath anymore :)) > ---- > Samples: 1K of event 'cycles', Event count (approx.): 186861492 > + 9.95% [k] kprobe_trace_func > + 6.00% [k] kprobe_ftrace_handler > + 5.53% [k] get_kprobe_cached
I should look at your filtering methods, maybe it can make ftrace filtering better?
> ---- > > Changes from v7: > - Re-evaluate the performance improvement. > > Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> > Cc: Steven Rostedt <rostedt@goodmis.org> > Cc: Frederic Weisbecker <fweisbec@gmail.com> > Cc: Ingo Molnar <mingo@redhat.com> > --- > include/linux/ftrace.h | 3 +++ > kernel/kprobes.c | 2 +- > kernel/trace/ftrace.c | 3 ++- > 3 files changed, 6 insertions(+), 2 deletions(-) > > diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h > index ae9504b..f1fa7d27 100644 > --- a/include/linux/ftrace.h > +++ b/include/linux/ftrace.h > @@ -93,6 +93,8 @@ typedef void (*ftrace_func_t)(unsigned long ip, unsigned long parent_ip, > * INITIALIZED - The ftrace_ops has already been initialized (first use time > * register_ftrace_function() is called, it will initialized the ops) > * DELETED - The ops are being deleted, do not let them be registered again. > + * SELF_FILTER - The ftrace_ops function filters ip by itself. Do not need to > + * check hash table on each hit.
- The ftrace_ops function has its own ip filter and does not need to rely on the ftrace internal ip filtering.
> */ > enum { > FTRACE_OPS_FL_ENABLED = 1 << 0, > @@ -105,6 +107,7 @@ enum { > FTRACE_OPS_FL_STUB = 1 << 7, > FTRACE_OPS_FL_INITIALIZED = 1 << 8, > FTRACE_OPS_FL_DELETED = 1 << 9, > + FTRACE_OPS_FL_SELF_FILTER = 1 << 10, > }; > > /* > diff --git a/kernel/kprobes.c b/kernel/kprobes.c > index 0f5f23c..5c6e410 100644 > --- a/kernel/kprobes.c > +++ b/kernel/kprobes.c > @@ -1027,7 +1027,7 @@ static struct kprobe *alloc_aggr_kprobe(struct kprobe *p) > #ifdef CONFIG_KPROBES_ON_FTRACE > static struct ftrace_ops kprobe_ftrace_ops __read_mostly = { > .func = kprobe_ftrace_handler, > - .flags = FTRACE_OPS_FL_SAVE_REGS, > + .flags = FTRACE_OPS_FL_SAVE_REGS | FTRACE_OPS_FL_SELF_FILTER, > }; > static int kprobe_ftrace_enabled; > > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c > index 4a54a25..062ca20 100644 > --- a/kernel/trace/ftrace.c > +++ b/kernel/trace/ftrace.c > @@ -4501,7 +4501,8 @@ __ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip, > */ > preempt_disable_notrace(); > do_for_each_ftrace_op(op, ftrace_ops_list) { > - if (ftrace_ops_test(op, ip, regs)) > + if (op->flags & FTRACE_OPS_FL_SELF_FILTER || > + ftrace_ops_test(op, ip, regs))
Hmm, I wonder if I should add the check for:
!(op->flags & FTRACE_OPS_FL_STUB)
here too? But that's another change that I'll do.
Just update the flag description as I commented and the rest looks good.
-- Steve
> op->func(ip, parent_ip, op, regs); > } while_for_each_ftrace_op(op); > preempt_enable_notrace(); >
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