[Oisf-devel] imporve flow table in workers runmode

[Victor Julien]

On 04/17/2013 04:35 PM, vpiserchia at gmail.com wrote:
>>>     >>> On Wed, 2013-04-03 at 15:40 +0200, Victor Julien wrote:
>>> >>     >>>> On 04/03/2013 10:59 AM, Chris Wakelin wrote:
>>> >>     >>>>> On 03/04/13 09:19, Victor Julien wrote:
>>> >>     >>>>>>> On 04/03/2013 02:31 AM, Song liu wrote:
>>> >>     >>>>>>>>>
>>> >>     >>>>>>>>> Right now, all workers will share one big flow table, and
>>> >>     there will be
>>> >>     >>>>>>>>> contention for it.
>>> >>     >>>>>>>>> Supposed that the network interface is flow affinity, each
>>> >>     worker will
>>> >>     >>>>>>>>> handle individual flows.
>>> >>     >>>>>>>>> In this way, I think it makes more sense that each worker
>>> >>     has its own
>>> >>     >>>>>>>>> flow table rather than one big table to reduce contention.
>>> >>     >>>>>>>>>
>>> >>     >>>>>>>
>>> >>     >>>>>>> We've been discussing this before and I think it would make
>>> >>     sense. It
>>> >>     >>>>>>> does require quite a bit of refactoring though, especially
>>> >>     since we'd
>>> >>     >>>>>>> have to support the current setup as well for the
>>> >>     non-workers runmodes.
>>> >>     >>>>>>>
> An other approach could be having something like a partitioned hash
> table with a fine-grained lock strategy.

We could do this, however I'd like to see some numbers first. I suspect
contention isn't really problematic in the flow engine right now.

> Even stronger could be using a lock-free data structures, does anyone
> have experience in this topic?

Some, and it's a really hard topic. Still interesting of course.

> The last alternative idea could be the usage of the userspace RCU
> implementation [1]

Also interesting, although last time I checked it used mutex' internally
for some book keeping. Still contention of those mutex' should be quite
a bit lower than in our case. Definitely worth looking into further.

-- 
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Victor Julien
http://www.inliniac.net/
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