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SubjectRe: [PATCH 14/28] ktap: add runtime/kp_events.[c|h]
(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.

Thank you,


--
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com




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