Re: Route cache performance

[Robert Olsson <Robert.Olsson@xxxxxxxxxxx>]

Simon Kirby writes:

 > Woot!
 > 
 > Yes, this is the difference.  With the patch applied (ajust directly
 > freeing the dst_entry), everything balances easily, there are no
 > overflows, and the result of rt_may_expire() looks very reasonable.
 > (Yay!)
 >
 > So, this seems to be the culprit.  Is NAPI supposed to allow the
 > queued bh to run or should we just not be queuing this?

 Packet processing happens in RX_SOFIRQ. NAPI or non-NAPI is no difference
 with RCU deferred delete this should happen by the RCU-tasklet when 
 tasklets are run after the real SOFTIRQ's.

 There is a limit for RCU work... maxbatch it's set to 10  you could back 
 out the patch and try increase it 1000/10000 so we know this not prevent 
 the freeing of entries. 

 module_param(maxbatch, int, 0);  /* rcupdate.c */
 
 Also RCU clearly states that is should be used in read-mostly situations
 rDoS is outside this scope. Anyway it would be interesting to understand 
 what's going on.

 Cheers.
                                                --ro