Intel 10Gb

[Andrew Gallatin]

Alexander Sack wrote:
<...>
 >> Using this driver/firmware combo, we can receive minimal packets at
 >> line rate (14.8Mpps) to userspace.  You can even access this using a
 >> libpcap interface.  The trick is that the fast paths are OS-bypass,
 >> and don't suffer from OS overheads, like lock contention.  See
 >> http://www.myri.com/scs/SNF/doc/index.html for details.
 >
 > But your timestamps will be atrocious at 10G speeds.  Myricom doesn't
 > timestamp packets AFAIK.  If you want reliable timestamps you need to
 > look at companies like Endace, Napatech, etc.


I see your old help ticket in our system.  Yes, our timestamping
is not as good as a dedicated capture card with a GPS reference,
but it is good enough for most people.

 > PS I am not sure but Intel also supports writing packets directly in
 > cache (yet I thought the 82599 driver actually does a prefetch anyway
 > which had me confused on why that helps)

You're talking about DCA.  We support DCA as well (and I suspect some
other 10G NICs do to).  There are a few barriers to using DCA on
FreeBSD, not least of which is that FreeBSD doesn't currently have the
infrastructure to support it (no IOATDMA or DCA drivers).

DCA is also problematic because support from system/motherboard
vendors is very spotty.  The vendor must provide the correct tag table
in BIOS such that the tags match the CPU/core numbering in the system.
Many motherboard vendors don't bother with this, and you cannot enable
DCA on a lot of systems, even though the underlying chipset supports
DCA.  I've done hacks to force-enable it in the past, with mixed
results. The problem is that DCA depends on having the correct tag
table, so that packets can be prefetched into the correct CPU's cache.
If the tag table is incorrect, DCA is a big pessimization, because it
blows the cache in other CPUs.

That said, I would *love* it if FreeBSD grew ioatdma/dca support.
Jack, does Intel have any interest in porting DCA support to FreeBSD?

Drew