You can use the snapshot feature to start recording whenever you
witness a significant latency[1].
You can use the system() function to trigger a record from your app.
e.g. system("lttng snapshot record");[1] http://lttng.org/docs/#doc-taking-a-snapshot I hope it helps. Francis On Wed, Feb 18, 2015 at 1:29 AM, zhenyu.ren <[email protected]> wrote: >> I think that might be a usecase for a profiler rather than a usecase for a >> tracer > > I am sorry that I have misled you.Not all write instances(a chance in a > million) take 100ms+ to complete.So I have to trace all write instances to > capture the deviant ones. > > Thanks > zhenyu.ren > > > > > > > ------------------------------------------------------------------ > 发件人：Francis Deslauriers <[email protected]> > > > 发送时间：2015年2月17日(星期二) 23:09 > 收件人：zhenyu.ren <[email protected]> > 抄 送：[email protected] <[email protected]> > 主 题：Re: 答复：[lttng-dev] Can lttng support kernel function tracer > > > CCing lttng-dev back in the thread. > > I might be wrong but I think that might be a usecase for a profiler > rather than a usecase for a tracer. Can someone else confirm? > To do that kind of work, you could compile your kernel with gprof support. > > Thanks, > Francis > > > On Tue, Feb 17, 2015 at 3:38 AM, zhenyu.ren <[email protected]> wrote: >> Hi,Francis >> In fact, I want to trace all kernel functions related to some >> behavior.For example,I write() and it returns 100ms later ,so I want to >> know which kernel function is too slow. In this case,I can use function >> tracer to trace "all" kernel function in the write() time window.However,I >> want to know is it possible that lttng can be useful in this case. >> >> Thanks >> zhenyu.ren >> >> >> ------------------------------------------------------------------ >> 发件人：Francis Deslauriers <[email protected]> >> 发送时间：2015年2月17日(星期二) 00:53 >> 收件人：zhenyu.ren <[email protected]> >> 抄 送：lttng-dev <[email protected]> >> 主 题：Re: [lttng-dev] Can lttng support kernel function tracer >> >> Hi Zhenyu, >> >> If I understandd your question correctly, I can think of two ways to >> trace an arbitrary kernel function. First, you can hook the tracer on >> a dynamic probe[1] using something like this: >> "lttng enable-event customEventName -k --probe kernelFunctionName". >> You can also hook the tracer on both entry and exit of a function >> using "--function" instead of "--probe". >> To list your kernel symbols use "cat /proc/kallsyms" >> Second, you can create custom kernel tracepoints and compile them in >> you kernel. Have a look at the online documentation [2]. >> >> Don't hesitate to explain further if this doesn't answer your question. >> >> Cheers! >> Francis >> >> [1] >> http://git.lttng.org/?p=lttng-tools.git;a=blob;f=doc/quickstart.txt;h=018c27b2b939ef7cd075255fd01bcfd8b2b21b1e;hb=HEAD#l93 >> [2] http://lttng.org/docs/#doc-instrumenting-linux-kernel-itself >> >> On Thu, Feb 12, 2015 at 7:49 PM, zhenyu.ren <[email protected]> wrote: >>> Hi, >>> >>> It's well known that lttng can make use of kernel tracepoints to do block >>> tracing ,system call tracing etc.Is it possible that lttng can produce >>> anything like kernel function tracer does? >>> >>> Thanks >>> zhenyu.ren >>> >>> _______________________________________________ >>> lttng-dev mailing list >>> [email protected] >>> http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev _______________________________________________ lttng-dev mailing list [email protected] http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
