[Haifux] A few issues from my PCIe lecture

[Eli Billauer]

Hi all,


There were a couple of issues you asked about, and I didn't address 
fully during the talk, so here we go:


Q: How do you detect a PCIe peripheral?

A: The answer is embarrassingly simple: lspci -vv gives you everything 
you wanted to know (and a lot you didn't). In particular, in the 
Capabilities section, if there's a capability name with "Express" in it 
appearing, it's a PCIe device.


Q: What about speed and performance?

A: lspci -vv again. It supplies both the (maximal) lane number and lane 
speed. As for packet overhead and squeezing every drop of bandwidth from 
the hardware, I talk about that in a recent post:


http://billauer.co.il/blog/?p=1119


As for the connection between my calculated upper limit (219 MB/sec) and 
reality, I consistently get 205 MB/sec with long dd transfers from 
hardware to PC (/dev/null, that is). Assuming I did nothing stupid, 
that's most likely the real-life limit. The CPU was at about 50% usage, 
and hardware writes way ahead of the read cursor, so I believe in this 
number.


    Eli

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Web: http://www.billauer.co.il