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Message-Id: <1B57F15E-49C6-4D62-8A2F-A3D54F783593@gmail.com> Date: Thu, 31 Oct 2013 16:40:12 -0700 From: Kenneth Lee <nek.in.cn@...il.com> To: Steven Rostedt <rostedt@...dmis.org> Cc: linux-kernel@...r.kernel.org Subject: Re: An small ftrace enhancement idea Thank you, Steve, Yes, with a separated instance, I can measure the latency for a stimulation while capture the other schedule events which I am interesting in. This is a better solution. I don’t know this “instance” stuff before. I don’t need to create another axe. I am sorry for my ignorance. Thanks and regards. --Kenneth 在 2013年10月31日，下午1:50，Steven Rostedt <rostedt@...dmis.org> 写道： > On Wed, 30 Oct 2013 15:39:50 -0700 > Kenneth Lee <nek.in.cn@...il.com> wrote: > >> Dear Steven, >> >> I want to add a new function to ftrace subsystem. Sometimes, we will face such a problem: system do not response to the input on time one to two times everyday. It is not easy to capture because it rarely happens. So I want to add a function to the kernel. If I have such problem, I insert a kernel module, who add a hook to the position that receive the input and another to the position that response to the input (with a session id if necessary). And I can compare the time between them and if the period is longer then a pre-set threshold, I can give a signal to a user helper application (maybe a script waiting on the file), which then can save the trace event to a file for later inspection. > > I'm a little confused in what you want. > > >> >> >> >> The user helper script may look like this: >> >> >> >> #/bin/sh >> >> >> >> echo ‘sched:*’ > /sys/kernel/debug/tracing/set_event >> >> modprobe delay_inspector.ko threshold=500 >> >> cat /sys/kernel/debug/tracing/waiter #wait for signal >> >> cp /sys/kernel/debug/tracing/trace /var/log/delay_infomation >> >> >> >> >> >> It looks like a standalone function. But I don’t have place to put it. Do you think I can implement it in ftrace? And do you think if there are better solution? >> > > You want something to wake up if it takes too long before an event > happens? > > If so, why not just use a select() on the trace_pipe and if it times > out, then dump the trace. You can even set up a separate instance. > > (this is waiting for a schedule switch to pid 1) > > cd /sys/kernel/debug/tracing > mkdir instances/mine > echo 'next_pid == 1' > instances/mine/events/sched/sched_switch/filter > echo 1 > instances/mine/events/sched/sched_switch/enable > > > The in a userspace program, I open "instances/mine/events/trace_pipe" > and run a select() on that file descriptor with a given timeout. If the > event does not happen within the expected time frame, the select > returns zero, and this userspace program can deal with it. > > Is that the functionality you are trying to achieve? > > -- Steve -- 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/
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