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    SubjectRe: 2.6.24-rc4-git5: Reported regressions from 2.6.23
    On Tue, 11 Dec 2007 00:34:33 +0100
    Stefano Brivio <stefano.brivio@polimi.it> wrote:

    > On Tue, 11 Dec 2007 00:04:25 +0100
    > Ingo Molnar <mingo@elte.hu> wrote:
    > >
    > > * Ingo Molnar <mingo@elte.hu> wrote:
    > >
    > > > * Andrew Morton <akpm@linux-foundation.org> wrote:
    > > >
    > > > > > what do you think? Right now i've got them queued up for
    > > > > > 2.6.25 in both the scheduler-devel and the x86-devel git
    > > > > > trees - but can submit them for 2.6.24 if it's better if we
    > > > > > did them there. I've got no strong opinion either way.
    > > > >
    > > > > printk_clock() doesn't seem terribly important but what's this
    > > > > stuff about effects on udelay/mdelay? That can be serious if
    > > > > they're getting shortened.
    > > >
    > > > since udelay depends on loops_per_jiffy, which is fixed up
    > > > time_cpufreq_notifier(), i dont see how it could be affected by
    > > > frequency changes. (but that's the theory - practice might be
    > > > different)
    > >
    > > Stefano Brivio reported udelay()/mdelay() effects in the b43
    > > driver. (and it caused driver failures for him.)
    > >
    > > Stefano, could you please try to sum up your experiences with that
    > > issue? Is it reproducable, and the 5 patches i did fix it? (if yes,
    > > could you try to re-do the mdelay verifications perhaps, to make
    > > sure it's not some other effect interacting here. In theory
    > > sched-clock scaling has no effect on udelay behavior.)
    >
    > Sorry for disappearing. Anyway, yes, those patches fixed it.
    > Precision in delays isn't that good when using my crappy unstable TSC
    > (mdelay(2000) causes delays between 2 and 2.9 seconds) but it's not
    > depending on frequency changes anymore. So I'd say it's fixed, but
    > please tell me if you want me to do any other test so as to be sure
    > it is.
    >
    >
    I'm still quite concerned about this in dual/quad core scenarios;
    the frequency of both cores is the maximum of what linux sets each core to;
    this means that if you're THIS sensitive to that there still is quite a nasty issue there.

    I wonder if the various delay functions (maybe only in .25) should use the maximum observed loops_per_jiffie instead always (across cpus) to be super safe here.

    --
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