[Xen-devel] RE: [PATCH] clocksource=tsc

["Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx>]

I'm thinking the problem may only occur when dom0 is
running ntpd.  Maybe "setting" the platform time only
changes one CPU, or sets the platform time differently
than system time?

> -----Original Message-----
> From: Keir Fraser [mailto:keir.fraser@xxxxxxxxxxxxx]
> Sent: Wednesday, July 16, 2008 6:50 AM
> To: dan.magenheimer@xxxxxxxxxx; Xen-Devel (E-mail)
> Cc: Dave Winchell
> Subject: Re: [PATCH] clocksource=tsc
> 
> 
> That's a weird set of symptoms. Perhaps dom0's sense of system time is
> diverging from Xen's? I don't see that CPUs can diverge, if 
> their TSCs are
> in sync, since we shouldn't be dynamically modifying the 
> per-CPU timestamps
> or scale factors.
> 
>  -- Keir
> 
> On 16/7/08 13:43, "Dan Magenheimer" 
> <dan.magenheimer@xxxxxxxxxx> wrote:
> 
> > Well now I have to take that back.  It DOESN'T work yet.
> > I think I am experiencing "Weirdness can happen..."
> > when booting with clocksource=tsc... I was away from
> > the machine overnight but the symptoms I've seen before
> > are that the system becomes less snappy and eventually
> > grinds to a near-halt.
> >
> > Oddly, I can login most of the way on the console
> > and launch new xterm's in my VNC display, but I never
> > get a prompt, and I can't interrupt a process I left
> > running overnight in another xterm.  The time display
> > in gnome seems to have frozen about an hour after
> > I booted.  Pinging the machine works but ssh'ing to
> > it doesn't ("Connection closed")
> >
> >> -----Original Message-----
> >> From: Dan Magenheimer [mailto:dan.magenheimer@xxxxxxxxxx]
> >> Sent: Tuesday, July 15, 2008 10:12 PM
> >> To: 'dan.magenheimer@xxxxxxxxxx'; 'Keir Fraser'; 
> 'Xen-Devel (E-mail)'
> >> Cc: 'Dave Winchell'
> >> Subject: RE: [PATCH] clocksource=tsc
> >>
> >>
> >> OK, ignore that.  It looks like you have it all fixed
> >> in 18060.  I tried it and it now boots.  Thanks!
> >>
> >>> -----Original Message-----
> >>> From: Dan Magenheimer [mailto:dan.magenheimer@xxxxxxxxxx]
> >>> Sent: Tuesday, July 15, 2008 7:16 PM
> >>> To: 'dan.magenheimer@xxxxxxxxxx'; 'Keir Fraser'; 'Xen-Devel
> >> (E-mail)'
> >>> Cc: 'Dave Winchell'
> >>> Subject: RE: [PATCH] clocksource=tsc
> >>>
> >>>
> >>>>>> Returning to 32-bit read_counter(), and having NULL
> >>>>> read_counter when
> >>>>>> clocksource=tsc would be another possibility...
> >>>
> >>> Well I hacked on 18055 for awhile and just couldn't get it
> >>> to boot.  I think local_time_calibration() (and thus
> >>> init_percpu_time()) is necessary for boot, though I'm not really
> >>> sure why.  Possibly the "Weirdness can happen..." comment in
> >>> that routine?
> >>>
> >>> Anyway, this patch (on top of 18055) DOES work, returns to the
> >>> 32-bit read_counter, and re-enables local_time_calibration().
> >>> I'd suggest putting off more major surgery for another day.
> >>>
> >>> Thanks,
> >>> Dan
> >>>
> >>>> -----Original Message-----
> >>>> From: Dan Magenheimer [mailto:dan.magenheimer@xxxxxxxxxx]
> >>>> Sent: Tuesday, July 15, 2008 10:04 AM
> >>>> To: dan.magenheimer@xxxxxxxxxx; Keir Fraser; Xen-Devel (E-mail)
> >>>> Cc: Dave Winchell
> >>>> Subject: RE: [PATCH] clocksource=tsc
> >>>>
> >>>>
> >>>> Hmmm... 18055 also fails to boot on my machine.
> >>>>
> >>>> Could we perhaps fall back to my original patch and do
> >>>> cleanup later/separately?  I also want to try implementing
> >>>> an hpet64-based get_s_time() so will be working more
> >>>> in this code later... but want to get clocksource=tsc
> >>>> working now with minimal code impact given the freeze.
> >>>>
> >>>>> -----Original Message-----
> >>>>> From: Dan Magenheimer [mailto:dan.magenheimer@xxxxxxxxxx]
> >>>>> Sent: Tuesday, July 15, 2008 9:46 AM
> >>>>> To: 'Keir Fraser'; 'Xen-Devel (E-mail)'
> >>>>> Cc: 'Dave Winchell'
> >>>>> Subject: RE: [PATCH] clocksource=tsc
> >>>>>
> >>>>>> Actually in this mode of operation we hardly need a platform
> >>>>>> timer *at all*.
> >>>>>> The idea is that we let the TSCs free-run, because we know
> >>>>>> they will behave.
> >>>>>> Returning to 32-bit read_counter(), and having NULL
> >>>>> read_counter when
> >>>>>> clocksource=tsc would be another possibility...
> >>>>>
> >>>>> That's essentially what the original tscstable.patch did, though
> >>>>> I was perhaps much uglier in the miscellaneous parts.
> >>>>>
> >>>>> Thanks,
> >>>>> Dan
> >>>>>
> >>>>
> >>>>
> >
> 
> 
>


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