[lttng-dev] Changed scheduling when using lttng

Mats Liljegren liljegren.mats2 at gmail.com
Fri Apr 26 11:31:47 EDT 2013

>> >> I tried number 1 using --read-timer 0, but "lttng stop" hanged at
>> >> "Waiting for data availability", producing lots of dots...
>> >
>> > As I said, we'd need to implement RING_BUFFER_WAKEUP_BY_WRITER when
>> > read-timer is set to 0. It's not implemented currently.
>> >
>> >>
>> >> Would it be possible to let some other (not using nohz mode) CPU to
>> >> flush the buffers?
>> >
>> > I guess that would be option 3) :
>> >
>> > Another option would be to let a single thread in the consumer handle
>> > the read-timer for all streams of the channel, like we do for UST.
>> Ehm, well, you did say something about implement... Sorry for missing that.
>> I guess now the question is which option that gives best
>> characteristics for least amount of work... Without knowing the design
>> of lttng-module, I'd believe that simply having the timer on another
>> CPU should be a good candidate. Is there anything to watch out for
>> with this solution?
>> Are there any documents describing lttng-module design, or is it "join
>> the force, use the source"? I've seen some high-level description
>> showing how tools/libs/modules fit together, but I haven't found
>> anything that describes how lttng-modules is designed.
> Papers on the ring buffer design exist, but not on lttng-modules per se.
> I think the best solution in the shortest amount of time would be (2):
> using deferrable timers. It's just flags to pass to timer creation.

Doesn't that require that the system is idle from time to time? My
application will occupy 100% CPU until finished, and expects there are
no ticks during that time.


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