(2014/05/08 19:59), Steven Rostedt wrote: > On Thu, 08 May 2014 18:39:30 +0900 > Masami Hiramatsu <[email protected]> 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?
Ah! Yes, it could be better :) At least the hash-table cache is good for ftrace too. Currently it is just for fixed-size hash-table, but is easy to expand for resizable one. (however, I guess with the cache we don't need to resize that anymore.) > >> ---- >> >> Changes from v7: >> - Re-evaluate the performance improvement. >> >> Signed-off-by: Masami Hiramatsu <[email protected]> >> Cc: Steven Rostedt <[email protected]> >> Cc: Frederic Weisbecker <[email protected]> >> Cc: Ingo Molnar <[email protected]> >> --- >> 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. OK, I'll update that. > > >> */ >> 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. Indeed. BTW, should I change ftrace_ops_control_func() too? > > Just update the flag description as I commented and the rest looks good. OK, thanks! -- Masami HIRAMATSU Software Platform Research Dept. Linux Technology Research Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: [email protected] -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
