Monday, 20 June 2011

dtrace update

I've updated dtrace to slightly improve the xcall code. Having tried
on an AS5 kernel - hit some other issues.

Some build issues are fixed (2.6.18 kernels confuse the syscall
extraction code); it mostly works - but some warnings are present.
Additionally, a 'dtrace -n syscall:::' will crash the kernel. I suspect
some mismatch on the ptregs syscalls and/or 32b syscalls on this kernel.
Need to debug.

Also found that on 16-core machine, the xcall code leads to a lot
of noise when things arent the way it expects. This eventually led
to an assertion failure in dtrace.c (on a buffer switch - which is
in agreement that the dtrace_sync() didnt hit the expected cpus, i.e.
some race condition/bug), and eventually a failure from the kernel that
a vm_free was invalid.

Oh dear.

To date I have been testing on dual-core cpus. I need to get an i7
so I can ramp up to 8 cores and do more heavy torture tests.

So, keep an eye out for updates (which are likely to be slow in
coming in next week or two), whilst I hopefully try to refine
the xcall issue.

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