Re: Some performance measurements on the FreeBSD network stack

On 20.04.2012 01:12, Andre Oppermann wrote:
> On 19.04.2012 22:34, K. Macy wrote:
>>>> This is indeed a big problem. I'm working (rough edges remain) on
>>>> changing the routing table locking to an rmlock (read-mostly) which
>>>
>>
>> This only helps if your flows aren't hitting the same rtentry.
>> Otherwise you still convoy on the lock for the rtentry itself to
>> increment and decrement the rtentry's reference count.
>
> The rtentry lock isn't obtained anymore. While the rmlock read
> lock is held on the rtable the relevant information like ifp and
> such is copied out. No later referencing possible. In the end
> any referencing of an rtentry would be forbidden and the rtentry
> lock can be removed. The second step can be optional though.
>
>>> i was wondering, is there a way (and/or any advantage) to use the
>>> fastforward code to look up the route for locally sourced packets ?
>>>
>>
>> If the number of peers is bounded then you can use the flowtable. Max
>> PPS is much higher bypassing routing lookup. However, it doesn't scale
 From my experience, turning fastfwd on gives ~20-30% performance 
increase (10G forwarding with firewalling, 1.4MPPS). ip_forward() uses 2 
lookups (ip_rtaddr + ip_output) vs 1 ip_fastfwd().
The worst current problem IMHO is number of locks packet have to 
traverse, not number of lookups.

>> to arbitrary flow numbers.

>
> In theory a rmlock-only lookup into a default-route only routing
> table would be faster than creating a flow table entry for every
> destination. It a matter of churn though. The flowtable isn't
> lockless in itself, is it?
>


-- 
WBR, Alexander