DTrace Support

[ryao]

It appears that Oracle is porting DTrace to Linux:

http://oss.oracle.com/git/?p=linux-2.6-dtrace-modules-beta.git;a=summary
http://oss.oracle.com/git/?p=linux-2.6-dtrace-unbreakable-beta.git;a=summary

We might be able to leverage this to enable us to debug issues involving ZFS.

[pyavdr]

Did you try it? Is it worth to try it ?

[ryao]

I have not tried it yet. ZFSOnLinux has no DTrace probes as far as I have seen. This would be more of a long term goal than something we could do right away.

[behlendorf]

There were some dtrace probes but they have been disabled since they didn't make any sense under Linux. Personally, I've found the Linux systemtap and ftrace utilities meet my needs, but to be honest I don't have much experience with DTrace. But if someone wants to make this work long term on Linux I'm all for it, the more tools the better.

[ryao]

There seems to be another dtrace port being done. This one appears to be an improvement on Oracle's port in that it is not tied to kernel versions that Oracle uses, although its build system does not appear to be as robust as ZFSOnLinux's build system:

https://github.com/dtrace4linux/linux

[behlendorf]

I'm convinced the cleanest thing we can do here is tie to dtrace probes to Linux kernel tracepoints. An initial version of this patch can be found in #2406. If at some point we can use the dtrace4linux port too that would be great, but porting dtrace is outside the scope of ZoL.