Re: Delete scheduler SD_WAKE_AFFINE and SD_WAKE_BALANCE flags

From: Nick Piggin (nickpiggin_at_yahoo.com.au)
Date: 07/29/05

  • Next message: Ingo Molnar: "Re: Delete scheduler SD_WAKE_AFFINE and SD_WAKE_BALANCE flags" 
    Date:	Fri, 29 Jul 2005 18:48:07 +1000
To: "Chen, Kenneth W" <kenneth.w.chen@intel.com>

    Chen, Kenneth W wrote:
    > Nick Piggin wrote on Thursday, July 28, 2005 7:01 PM

    > This clearly outlines an issue with the implementation. Optimize for one
    > type of workload has detrimental effect on another workload and vice versa.
    >

    Yep. That comes up fairly regularly when tuning the scheduler :(

    >
    > I won't try to compromise between the two. If you do so, we would end up
    > with two half baked raw turkey. Making less aggressive load balance in the
    > wake up path would probably reduce performance for the type of workload you
    > quoted earlier and for db workload, we don't want any of them at all, not
    > even the code to determine whether it should be balanced or not.
    >

    Well, that remains to be seen. If it can be made _smarter_, then you
    may not have to take such a big compromise.

    But either way, there will have to be some compromise made. At the
    very least you have to find some acceptable default.

    > Do you have an example workload you mentioned earlier that depends on
    > SD_WAKE_BALANCE? I would like to experiment with it so we can move this
    > forward instead of paper talk.
    >

    Well, you can easily see suboptimal scheduling decisions on many
    programs with lots of interprocess communication. For example, tbench
    on a dual Xeon:

    processes 1 2 3 4

    2.6.13-rc4: 187, 183, 179 260, 259, 256 340, 320, 349 504, 496, 500
    no wake-bal: 180, 180, 177 254, 254, 253 268, 270, 348 345, 290, 500

    Numbers are MB/s, higher is better.

    Networking or other IO workloads where processes are tightly coupled
    to a specific adapter / interrupt source can also see pretty good
    gains. 

    -- 
SUSE Labs, Novell Inc.
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  • Next message: Ingo Molnar: "Re: Delete scheduler SD_WAKE_AFFINE and SD_WAKE_BALANCE flags"

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