[lttng-dev] Stream trace data over PCIe (or anything else)

[Simon Marchi]

Hello LTTng cyborgs,

As some of you might know, I am trying to port and adapt LTTng to the
Tilera TILEncore-Gx card (and later the Intel Xeon Phi). The main
constraint with these platforms is the non existent disk space, which
means the trace will have to be streamed. I am thinking of using the
PCI express connection the two cards have to stream the trace data and
save it on the host. It seems like this use case is similar to what
the network consumer and relayd offer, but simply on another medium.

The consumer currently has two destination types: local and net (enum
consumer_dst_type in bin/lttng-sessiond/consumer.h). I understand that
I could create another type of consumer which sends data over the PCI
port instead. On the other side of the bus, I could adapt relayd to
receive on the PCI port of the host and save the trace as it currently
does for the network.

I would like to hear your comments about this approach. Does it sound
right, is there a better way ? Would it be worth it to design a system
that would make it easier to add a new type of "transport" for the
trace data ?

Thanks !

Simon