On 06.11.2012 12:02, Fabien Thomas wrote:
Hi Luigi,
do you agree on polling having outlived its usefulness in the light
of interrupt moderating NIC's and SMP complications/disadvantages?
If you have only one interface yes polling is not really necessary.
If you have 10 interfaces the interrupt moderation threshold is hard to find
to not saturate the system.
Doing polling at 8000hz in that case is a lot better regarding global interrupt
level.
OK. Is the problem the interrupt load itself, or the taskqueues?
The problem is that in the current state polling does not work well and people
remember
the good old time where polling was better.
Indeed.
rstone@ and myself have made some improvement to polling.
You can find a diff here for 8.3 with updated intel driver :
http://people.freebsd.org/~fabient/polling/patch-pollif_8.3_11052012
- support multiqueue for ixgbe, igb, em.
- compat API for old driver
- keep interrupt for link / status
- user core mapping / auto mapping
- deadline to keep cpu available
- integrated to netisr
- deferred packet injection with optional prefetching
This is a number of interesting but sometimes only tangentially
related features. Lets focus on the network cpu monopolization
issue first.
Performance are on par with interrupt but you can keep a system alive more
easily
by accounting all network processing for the deadline (with direct dispatch).
Would you be willing to work a solution with me with a load aware
taskqueue as I proposed in a recent email to Luigi? That way we
don't need special cases or features or even a normal server under
DDoS wouldn't go down.
--
Andre
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