On Fri, 24 Aug 2007 21:04:56 +0200 Bodo Eggert <[EMAIL PROTECTED]> wrote:
> Linas Vepstas <[EMAIL PROTECTED]> wrote: > > On Fri, Aug 24, 2007 at 03:59:16PM +0200, Jan-Bernd Themann wrote: > > >> 3) On modern systems the incoming packets are processed very fast. > >> Especially > >> on SMP systems when we use multiple queues we process only a few packets > >> per napi poll cycle. So NAPI does not work very well here and the interrupt > >> rate is still high. > > > > I saw this too, on a system that is "modern" but not terribly fast, and > > only slightly (2-way) smp. (the spidernet) > > > > I experimented wih various solutions, none were terribly exciting. The > > thing that killed all of them was a crazy test case that someone sprung on > > me: They had written a worst-case network ping-pong app: send one > > packet, wait for reply, send one packet, etc. > > > > If I waited (indefinitely) for a second packet to show up, the test case > > completely stalled (since no second packet would ever arrive). And if I > > introduced a timer to wait for a second packet, then I just increased > > the latency in the response to the first packet, and this was noticed, > > and folks complained. > > Possible solution / possible brainfart: > > Introduce a timer, but don't start to use it to combine packets unless you > receive n packets within the timeframe. If you receive less than m packets > within one timeframe, stop using the timer. The system should now have a > decent response time when the network is idle, and when the network is > busy, nobody will complain about the latency.-) I expect the overhead of OS timers and resolution makes this unsuitable for fast networks. You need the hardware to do it. On slow networks, it doesn't matter. -- Stephen Hemminger <[EMAIL PROTECTED]> - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
