Tracking memory, PCI(-E) bus usage?

[Ivan Voras]

This is mostly idle wanderings than anything useful, but I've just
redirected an application which creates a lot of temporary data to a
tmpfs mount point and I'm happily observing disk bandwidth dwindling
from a sustained many dozens of MB/s to merely hundreds of KB/s, which
is the value the system was designed for.

That got me thinking that I would also be happy if I could observe the
bandwidth used by the memory file system, and even memory in total, and
by extension, the traffic on various busses.

So this is the question for people who twiddle with the hardware level:
is there a way in which those quantities could be tracked in real-time?
For the memory, I guess it would depend on the memory controller, but
even memory controllers are built-in in recent CPUs, which means there
could be a way. I'm vaguely recalling that PCI-E (at least) works in
some kind of packet-based transaction mode so it seems possible that it
could also offer some metrics.


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