lkml.org 
[lkml]   [2007]   [Aug]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    SubjectRe: RFC: issues concerning the next NAPI interface
    Date
    Hi,

    On Friday 24 August 2007 17:37, akepner@sgi.com 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. What we need would be some sort of timer polling mode
    > >    which will schedule a device after a certain amount of time for high load
    > >    situations. With high precision timers this could work well. Current
    > >    usual timers are too slow. A finer granularity would be needed to keep the
    > > latency down (and queue length moderate).
    > >
    >
    > We found the same on ia64-sn systems with tg3 a couple of years
    > ago. Using simple interrupt coalescing ("don't interrupt until
    > you've received N packets or M usecs have elapsed") worked
    > reasonably well in practice. If your h/w supports that (and I'd
    > guess it does, since it's such a simple thing), you might try
    > it.
    >

    I don't see how this should work. Our latest machines are fast enough that they
    simply empty the queue during the first poll iteration (in most cases).
    Even if you wait until X packets have been received, it does not help for
    the next poll cycle. The average number of packets we process per poll queue
    is low. So a timer would be preferable that periodically polls the
    queue, without the need of generating a HW interrupt. This would allow us
    to wait until a reasonable amount of packets have been received in the meantime
    to keep the poll overhead low. This would also be useful in combination
    with LRO.

    Regards,
    Jan-Bernd
    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2007-08-24 17:51    [W:3.322 / U:0.040 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site