Re: Device polling, kern.polling.burst_max and gig-e

From: Steve Francis (steve_at_expertcity.com)
Date: 01/30/04

  • Next message: Luigi Rizzo: "Re: Device polling, kern.polling.burst_max and gig-e" 
    Date: Fri, 30 Jan 2004 10:46:06 -0800
To: Luigi Rizzo <rizzo@icir.org>

    Luigi Rizzo wrote:

    >i would probably increase HZ to 2000 and burst_max to 300-400,
    >not much more though otherwise you are going to spend too much
    >time in the timer handler.
    >In any case, i don't think the card is able to go above 6-700kpps.
    >
    >
    OK, thanks.
    Each card is only being asked to do (at most ) 250kpps. Two cards with
    that load in the system.

    No tuning of

    kern.polling.each_burst recommended?
    Thanks

    >If you are having a lot of load, it is natural that you are
    >going to get losses, the 2sec period is probably how often the
    >nic updates the stats.
    >
    > cheers
    > luigi
    >
    >On Fri, Jan 30, 2004 at 10:34:08AM -0800, Steve Francis wrote:
    >
    >
    >>We have a 4.9-RELEASE-p1 box dedicated to some traffic analysis. It
    >>monitors on two em interfaces: about 200,000 pps on one interface, and
    >>180,000 pps on the other.
    >>It's been dealing with that OK, but our traffic levels are increasing -
    >>we reached over 240,000 pps on one interface last week. This made CPU
    >>reach 100%, and some packets not get processed.
    >>So, last night we enabled polling on the nics.
    >>Initially, great result - CPU dropped from 82% load (45% system load due
    >>to interupts) yesterday to 55% load today (12% in system), for same pps
    >>load (about 300,000 pps total) at the time.
    >>
    >>However, input errors went from 0 to about 1200 (oddly, it was 1200
    >>every other second, and 0 for the seconds in-between.)
    >>
    >>A bit of digging around led me to increase kern.polling.burst_max.
    >>According to http://info.iet.unipi.it/~luigi/polling/, "The default
    >>value is enough for a 100Mbit ethernet". I increased it gradually to
    >>900, whcih has almost (but not entirely) eliminated the errors. Now the
    >>errors are zero for most intervals, but every 10 or so intervals there
    >>are between 10 and 100 input errors.
    >>
    >>So:
    >>- does it make sense to leave the default at 150, in this day of gigabit
    >>nics?
    >>- is there a danger in increasing the burt_max? (My burst size goes
    >>straight to the max of 900.)
    >>- can it be increased more ?
    >>- are there other variables that make sense to increase for gigabit?
    >>(like kern.polling.each_burst:?)
    >>
    >>Since I increased the burst max, I now have slowly incrementing
    >>kern.polling.lost_polls - about 1 every 2 seconds. Anything to worry about?
    >>
    >>Thanks
    >>Steve Francis
    >>
    >>
    >>
    >>
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    >>

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