Date: Thu, 2 Jul 2015 09:30:38 -0700 From: abhishek kulkarni <abhya007@gmail.com> To: Ryan Stone <rysto32@gmail.com> Cc: Ryan Stone <rstone@freebsd.org>, "freebsd-dtrace@freebsd.org" <freebsd-dtrace@freebsd.org> Subject: Re: Regarding schedgraph.d Message-ID: <CAJUVseuHN-hLvLP6AQZdjwnQqpB24nSfm-dAWmn=j3y1EYiEMw@mail.gmail.com> In-Reply-To: <CAFMmRNwu8SoX-dJPb1wBh26UnXAnM5x7FZprDmXpVXbS7htkYQ@mail.gmail.com> References: <CAJUVsesOHQegeS=yfED8iKUoJK5KEVnLBqKH1MpSUuH_4i=_RQ@mail.gmail.com> <CAFMmRNwu8SoX-dJPb1wBh26UnXAnM5x7FZprDmXpVXbS7htkYQ@mail.gmail.com>
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Thanks Ryan. Those are some very useful tips. Ill get on with trying all of
those and get back If I have some more concerns. Also, could you be having
some document which has some logical description about the "sched" probes
for FreeBSD, which could give details like when is the particular probe
fired, the probe's arguments etc. Thanks again.
Regards
Abhishek Kulkarni
On Wed, Jul 1, 2015 at 1:51 PM, Ryan Stone <rysto32@gmail.com> wrote:
> On Tue, Jun 30, 2015 at 7:11 PM, abhishek kulkarni <abhya007@gmail.com>
> wrote:
>
>> Hello Ryan,
>>
>> I was looking to schedgraph.d . I need to modify the script for a
>> single, particular thread. I atleast need to know the thread transitions,
>> as in the context switches for the particular thread and also the different
>> states for a single thread. Could you please help with the filters that I
>> need to add in order to use the script for a single thread or else suggest
>> me just the nexessary probes that I could use for writing a new script for
>> a single thread .
>>
>> Regards
>> Abhishek Kulkarni
>>
>
> There are a couple of things that you could filter on, depending on what
> you know about the thread of interest. The "execname" variable gives the
> name of the current process. If you're interesting in tracing a
> single-threaded process, that would be an option. Another variable of
> interest would be the "curthread" variable. This gives a pointer to the
> "struct thread" for the current thread. One field that you could trace on
> would be curthread->td_tid. You can use ps to find your thread id and then
> run the script as:
>
> dtrace -s script.d <tid>
>
> And in the script, filter with / curthread->td_tid == $1 /. Another field
> that you could use would be curthread->td_name, which contains the name of
> the current thread. If your application names threads with
> "pthreads_set_name_np()", then that name will appear in td_name and you can
> filter based off of that.
>
> An alternative approach would be to use a thread-local variable. If you
> know that your thread is the only thread that might hit a probe, you can
> set a thread local variable in that probe and filter on it later on. For
> example, if your thread is the only thread that will call a function called
> foobar() in the kernel, you could do this:
>
> fbt::foobar:entry
> {
> self->interesting = 1;
> }
>
> sched:::off-cpu
> / self->interesting /
> {
> /* trace interesting data here */
> }
>
>
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