ixgbe/NFS m_defrag() instrumentation

[Scott Long]

On Feb 4, 2014, at 10:27 PM, Garrett Wollman <wollman at freebsd.org> wrote:

> I instrumented calls to m_defrag() in ixgbe.  As expected, it gets
> called *a lot* when NFS is running with the default read size of 64k.
> A simple benchmark (single-threaded sequential read of a 128 GB file
> which I didn't even run to completion) tells the tale:
> 
> $ sysctl dev.ix.0.mbuf_defrag_attempted
> dev.ix.0.mbuf_defrag_attempted: 1737994
> 
> (There's already a similar counter for m_defrag() failures, which made
> it easy to add this counter.  Unfortunately, there is no analogous
> instrumentation in cxgbe so I couldn't do likewise for that NIC.)


dtrace to the rescue?

#!/usr/sbin/dtrace -s
fbt::m_defrag:entry
{
	@ = count();
}