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    Subject[patch] fix for sched_clock() when using jiffies


    I'm in the process of updating a port for an ARM based chip we've been
    working on, from 2.6.22-rc4'ish to the current HEAD of Linus' tree, and
    I started seeing the following:

    [ 0.000000] PID hash table entries: 512 (order: 9, 2048 bytes)
    [42949372.970000] Dentry cache hash table entries: 16384 (order: 4, 65536 bytes)

    The reason appears to be that printk_clock() has been replaced with a
    call to cpu_clock, which in our case currently falls back to the default
    (weak) implementation of sched_clock() that uses jiffies -- but doesn't
    account for the initial offset of the jiffy count. The following simple
    patch fixes it for me, in line with what printk_clock used to do.


    diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c
    index 8178724..d76814e 100644
    --- a/kernel/sched_clock.c
    +++ b/kernel/sched_clock.c
    @@ -37,7 +37,7 @@
    unsigned long long __attribute__((weak)) sched_clock(void)
    - return (unsigned long long)jiffies * (NSEC_PER_SEC / HZ);
    + return (unsigned long long)(jiffies - INITIAL_JIFFIES) * (NSEC_PER_SEC / HZ);

     \ /
      Last update: 2008-11-26 16:43    [W:0.021 / U:10.460 seconds]
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