[dpdk-dev] Appropriate DPDK data structures for TCP sockets
Matthew Hall
mhall at mhcomputing.net
Mon Feb 23 22:16:45 CET 2015
On Mon, Feb 23, 2015 at 08:48:57AM -0600, Matt Laswell wrote:
> Apologies in advance for likely being a bit long-winded.
Long winded is great, helps me get context.
> First, you really need to take cache performance into account when you're
> choosing a data structure. Something like a balanced tree can seem awfully
> appealing at first blush
Agreed. I did some amount of DPDK stuff before but without TCP. This is why I
was figuring a packet-hash is better than a tree.
> Second, rather than synchronizing (perhaps with locks, perhaps with
> lockless data structures), it's often beneficial to create multiple
> threads, each of which holds a fraction of your connection tracking data.
Yes, I REALLY REALLY REALLY wanted to do RSS. But the virtio-net and other
VM's don't support RSS, unlike the classic PCIe NIC's. In order to get the
community to use my app I have to give them a "batteries included"
environment, where the system can still work even with no RSS.
> Third, it's very worthwhile to have a cache for the most recently accessed
> connection. First, because network traffic is bursty, and you'll
> frequently see multiple packets from the same connection in succession.
> Second, because it can make life easier for your application code. If you
> have multiple places that need to access connection data, you don't have to
> worry so much about the cost of repeated searches. Again, this may or may
> not matter for your particular application. But for ones I've worked on,
> it's been a win.
Yes, this sounds like a really good idea. One advantage in my product, I am
only doing TCP Syslog, so I don't have an arbitrary zillion connections like
FW or IPS would want. I could cap it at something like 8192 or 16384 and be
good enough for some time until a better solution is worked out.
I could make some capped array or linked list of the X most recent ones for
cheap access. It's just socket pointers so it doesn't hardly cost anything to
copy a couple pointers into a cache and quickly invalidate when the connection
closes.
> Anyway, as predicted, this post has gone far too long for a Monday
> morning. Regardless, I hope you found it useful.
This was great. Thank you!
Matthew.
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