[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CAGdX0WHarh12K_2D8M=UAtwEJaZr_eZupXzsw-SXqd2X4NGTmg@mail.gmail.com>
Date: Mon, 31 Mar 2014 18:14:31 +0800
From: Jovi Zhangwei <jovi.zhangwei@...il.com>
To: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc: Ingo Molnar <mingo@...hat.com>,
Steven Rostedt <rostedt@...dmis.org>,
LKML <linux-kernel@...r.kernel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 14/28] ktap: add runtime/kp_events.[c|h]
On Mon, Mar 31, 2014 at 5:10 PM, Masami Hiramatsu
<masami.hiramatsu.pt@...achi.com> wrote:
> (2014/03/28 22:47), Jovi Zhangwei wrote:
>> kp_events.c handle ktap events management(registry, destroy, event callback)
>>
>> This file is core event management interface between ktap and kernel.
>>
>> Exposed functions:
>> 1). kp_events_init/kp_events_exit
>>
>> 2). kp_event_create_kprobe
>> create kprobe event, for example:
>> kdebug.kprobe("SyS_futex", function () {})
>>
>> 3). kp_event_create_tracepoint
>> create tracepoint event, for example"
>> kdebug.tracepoint("sys_futex_enter", function () {})
>>
>> 4). kp_event_create
>> create perf backend event, for example:
>> trace sched:sched_switch { print(argstr) }
>>
>> It call kernel function 'perf_event_create_kernel_counter' to
>> register event(tracepoint/kprobe/uprobe)
>>
>> 5). kp_event_getarg
>> get argument of event, from arg0 to arg9,
>> only can be called in probe context.
>> trace sched:sched_switch { print(arg0, arg1) }
>>
>> 6). kp_event_stringify/kp_event_tostr
>> stringify argstr, sometimes if store argstr as key to table,
>> then it need to stringify firstly, like below:
>> var s={} trace sched:sched_switch { s[argstr] += 1 }
>> (This is quite rare usage, but ktap support it)
>>
>> Note:
>> Why ktap support 'kdebug.kprobe' and 'kdebug.tracepoint' when
>> it already support perf backend event(trace xxx {})?
>>
>> Because benchmark shows raw kprobe and tracpoint interface is faster
>> than perf backed tracing, nearly 10+%, it's more fair to compare
>> with Systemtap by raw tracing syntax, not perf backend tracing.
>>
>
> Do we really need it just for a +10% performance? I doubt that.
> I think the benefit point of ktap is "dynamic & simple programmable
> tracer in kernel", not the good performance at least at this point.
> Thus I think we should start ktap only with perf backend.
>
Yeah, agreed, most people like the perf-backed tracing syntax,
that raw trace interface is just for benchmark when I wanted to look
overhead compare with stap, the result is very inspiring, ktap table
operation overhead is lower than stap.
On the performance overhead of dynamic tracing tools(ktap/stap/dtrace),
it's interesting enough that dtrace was used in production many year,
_but_ IMO the runtime of dtrace is slow after I checked dtrace source
code :), system workload does big matter than tracing tool overhead.
Thanks.
Jovi
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists