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Re: Re: [PATCH -tip v10 7/7] ftrace: Introduce FTRACE_OPS_FL_SELF_FILTER for ftrace-kprobe
- From: Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>
- To: Steven Rostedt <rostedt at goodmis dot org>
- Cc: linux-kernel at vger dot kernel dot org, Ingo Molnar <mingo at kernel dot org>, Andi Kleen <andi at firstfloor dot org>, Ananth N Mavinakayanahalli <ananth at in dot ibm dot com>, Sandeepa Prabhu <sandeepa dot prabhu at linaro dot org>, Frederic Weisbecker <fweisbec at gmail dot com>, x86 at kernel dot org, fche at redhat dot com, mingo at redhat dot com, systemtap at sourceware dot org, "H. Peter Anvin" <hpa at zytor dot com>, Thomas Gleixner <tglx at linutronix dot de>
- Date: Fri, 09 May 2014 12:11:29 +0900
- Subject: Re: Re: [PATCH -tip v10 7/7] ftrace: Introduce FTRACE_OPS_FL_SELF_FILTER for ftrace-kprobe
- Authentication-results: sourceware.org; auth=none
- References: <20140508093842 dot 31767 dot 43766 dot stgit at ltc230 dot yrl dot intra dot hitachi dot co dot jp> <20140508093930 dot 31767 dot 86419 dot stgit at ltc230 dot yrl dot intra dot hitachi dot co dot jp> <20140508065947 dot 214f4951 at gandalf dot local dot home>
(2014/05/08 19:59), Steven Rostedt wrote:
> 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?
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 <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.
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: masami.hiramatsu.pt@hitachi.com