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    SubjectRe: 2.6.21 -> 2.6.22 & 2.6.23-rc8 performance regression
    Denys a écrit :
    > Well, i can play a bit more on "live" servers. I have now hot-swap server with
    > full gentoo, where i can rebuild any kernel you want, with any applied patch.
    > But it looks more like not overhead, load becoming high too "spiky", and it is
    > not just permantenly higher. Also it is not normal that all system becoming
    > unresposive (for example ping 127.0.0.1 becoming 300ms for period, when usage
    > softirq jumps to 100%).
    >
    >
    Could you try a pristine 2.6.22.9 and some patch in
    secure_tcp_sequence_number() like :

    --- drivers/char/random.c.orig 2007-10-01 10:18:42.000000000 +0200
    +++ drivers/char/random.c 2007-10-01 10:19:58.000000000 +0200
    @@ -1554,7 +1554,7 @@
    * That's funny, Linux has one built in! Use it!
    * (Networks are faster now - should this be increased?)
    */
    - seq += ktime_get_real().tv64;
    + seq += ktime_get_real().tv64 / 1000;
    #if 0
    printk("init_seq(%lx, %lx, %d, %d) = %d\n",
    saddr, daddr, sport, dport, seq);

    Thank you


    > On Mon, 01 Oct 2007 00:12:59 -0700 (PDT), David Miller wrote
    >
    >> From: Eric Dumazet <dada1@cosmosbay.com>
    >> Date: Mon, 01 Oct 2007 07:59:12 +0200
    >>
    >>
    >>> No problem here on bigger servers, so I CC David Miller and netdev
    >>> on this one. AFAIK do_gettimeofday() and ktime_get_real() should
    >>> use the same underlying hardware functions on PC and no performance
    >>> problem should happen here.
    >>>
    >> One thing that jumps out at me is that on 32-bit (and to a certain
    >> extent on 64-bit) there is a lot of stack accesses and missed
    >> optimizations because all of the work occurs, and gets expanded,
    >> inside of ktime_get_real().
    >>
    >> The timespec_to_ktime() inside of there constructs the ktime_t return
    >> value on the stack, then returns that as an aggregate to the caller.
    >>
    >> That cannot be without some cost.
    >>
    >> ktime_get_real() is definitely a candidate for inlining especially in
    >> these kinds of cases where we'll happily get computations in local
    >> registers instead of all of this on-stack nonsense. And in several
    >> cases (if the caller only needs the tv_sec value, for example)
    >> computations can be elided entirely.
    >>
    >> It would be constructive to experiment and see if this is in fact
    >> part of the problem.
    >>
    >
    >
    > --
    > Denys Fedoryshchenko
    > Technical Manager
    > Virtual ISP S.A.L.
    >
    >
    >



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