Messages in this thread | | | Date | Wed, 15 Sep 2010 00:18:14 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [BISECTED] 2.6.35.*: horrible (exponential? >linear) slowdown to unusability (HPET) |
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On Tue, 14 Sep 2010, Nix wrote:
> On 14 Sep 2010, Thomas Gleixner said: > > > On Fri, 10 Sep 2010, Thomas Gleixner wrote: > >> On Fri, 10 Sep 2010, Nix wrote: > >> > > >> > I suspect current_clocksource doesn't do what we think it does, or the > >> > clocksource and 'clock event device' are not the same.) > >> > >> Right, they are not the same. clocksource provides us a read out > >> device for timekeeping (usually a simple increasing counter). clock > >> event device is used to generate timer interrupts. > >> > >> HPET provides both functionalities. > >> > >> The patch you bisected is affecting the clock events part of the > >> HPET. So yes, it's not a clock source problem. > > > > Another question. If you add hpet=verbose (or revert that commit) does > > the printk_once in hpet_set_next_event() show up in dmesg ? > > > > "hpet: compare register read back failed." > > Well, given that I reverted that commit in the past (during the > bisection) and also added hpet=verbose[1], I'd have expected it to turn > up in my past syslogs. There is no sign of it, in syslogs back to 2009. > > > [1] and indeed am running 2.6.35.4 with hpet=verbose and no symptoms > on the affected system *now* -- a mystery because I thought the > hpet=verbose-turns-it-off code was removed, but turning on verbose > still seems to quash the bug?! or perhaps it's slightly > intermittent and every N boots I'm lucky enough to miss it. I'm > slightly chary of rebooting to find out ;}
hpet=verbose forces the read back.
FYI, we got a reasonable explanation now what's going on in hardware land. Patch is in the works.
Thanks,
tglx
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