On 11 February 2013 13:22, Dan Shechter <dans...@gmail.com> wrote: > Thanks. > > If interrupt mitigation disabling won't be enough I will have do > decide: freebs with netmap or openbsd with if_ethersubr.c > modification. > > netmap looks much easier to code. No need to do the mbuf dance (or I > hope that with netmap there would be no such need). > > BTW, would HW TX IP/UDP checksum reduce the latency?
I don't know exactly, but compared to the amount of work done by bpf/pcap and syscalls (at least write), I'd say it's negligible. > Best regards, > Dan > > > On Mon, Feb 11, 2013 at 2:11 PM, Mike Belopuhov <m...@belopuhov.com> wrote: >> On 11 February 2013 12:53, Dan Shechter <dans...@gmail.com> wrote: >>> Thanks, >>> >>> Are there any other tips to reduce latency? >>> >> >> Using pcap means copying packets, so I'd say you want to >> put your code into the kernel to avoid copying and maybe >> queueing as well, but this is not something that can be >> trivially explained and is certainly not something that >> OpenBSD supports or would want to support out of the box. >> >> FreeBSD netmap interface would be helpful in your situation >> but is not currently supported by OpenBSD. >> >> Cheers, >> Mike >> >>> >>> Best regards, >>> Dan >>> >>> >>> On Mon, Feb 11, 2013 at 1:43 PM, Mike Belopuhov <m...@belopuhov.com> wrote: >>>> On 11 February 2013 12:19, Dan Shechter <dans...@gmail.com> wrote: >>>>> Hi All, >>>>> >>>>> I have a very latency sensitive application. I need to move packets >>>>> from one interface to another >>>>> >>>>> I am using a quad 1000/pro Intel NIC. pcidump shows 82571EB >>>>> >>>>> My latency sensitive application reads packets from one em interface >>>>> using libpcap and sends packet to another em interface using udp >>>>> socket. >>>>> >>>>> Does em has interrupt mitigation enabled? >>>> >>>> It does. >>>> >>>>> If interrupt mitigation is enabled would disabling it will reduce latency? >>>> >>>> It would. >>>> >>>>> How can I disable the interrupt mitigation for em NICs? >>>> >>>> I suggest you try increasing MAX_INTS_PER_SEC define by the factor >>>> or two in /sys/dev/pci/if_em.h. In case it doesn't suite your needs you >>>> can try commenting out this line: >>>> >>>> E1000_WRITE_REG(&sc->hw, ITR, DEFAULT_ITR); >>>> >>>>> What would change in 5.3? >>>>> >>>> >>>> Nothing regarding interrupt moderation. >>>> >>>>> Best regards, >>>>> Dan >>>>> >>>> >>>> Cheers, >>>> Mike
