lkml.org 
[lkml]   [2010]   [Oct]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [bisected] Clocksource tsc unstable git
    On Fri, Oct 29, 2010 at 08:14:12AM -0400, Thomas Gleixner wrote:
    > On Fri, 29 Oct 2010, Borislav Petkov wrote:
    > > On Fri, Oct 29, 2010 at 04:30:13AM -0400, Markus Trippelsdorf wrote:
    > > That's strange, when we tested this one everything seemed fine so I
    > > guess this is one of those bugs which appear later, just as if out of
    > > nowhere.
    > >
    > > Thomas, could it be that SMI fires in between the HPET write and
    > > subsequent read:
    > >
    > > hpet_writel(cnt, HPET_Tn_CMP(timer));
    > >
    > > ...
    > >
    > > res = (s32)(cnt - hpet_readl(HPET_COUNTER));
    > >
    > > causing the -ETIME and thus a wait for HPET wraparound? My machine at
    > > least does SMI-initiated C1E so it could very well be the problem.
    >
    > Well, even if a SMI fires, then the counter will be ahead of cnt and
    > we get -ETIME. The upper layer of clockevents/timers will then
    > reprogram HPET. So that's not an issue.

    Ah, I missed the upper layer, good.

    > The only problem which might hit us is when our assumption of 8 HPET
    > cycles being enough to transfer the new match value into the real
    > match register is wrong.

    So Markus, can you try with 995bd3bb5c78, but by increasing the value
    to, say 16 (I don't know what's a good value here, let's double the old
    one). Simply change the line

    return res < 8 ? -ETIME : 0;

    to

    return res < 16 ? -ETIME : 0;


    in <arch/x86/kernel/hpet.c:hpet_next_event()>. I'll do that too on the
    machine here when I get around to it.

    Thanks.

    --
    Regards/Gruss,
    Boris.

    Advanced Micro Devices GmbH
    Einsteinring 24, 85609 Dornach
    General Managers: Alberto Bozzo, Andrew Bowd
    Registration: Dornach, Gemeinde Aschheim, Landkreis Muenchen
    Registergericht Muenchen, HRB Nr. 43632


    \
     
     \ /
      Last update: 2010-10-29 19:23    [W:0.028 / U:61.552 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site