Re: [Xen-devel] CONFIG_NO_HZ + CONFIG_CPU_IDLE freeze the system (Was Re: [PATCH] acpi : remove power from acpi_processor_cx structure)

[John Stultz <john.stultz@xxxxxxxxxx>]

On 09/07/2012 02:35 PM, Daniel Lezcano wrote:
> On 09/07/2012 07:22 PM, John Stultz wrote:
> > On 09/07/2012 07:20 AM, Daniel Lezcano wrote:
> > > On 09/06/2012 11:18 PM, Rafael J. Wysocki wrote:
> > > > On Thursday, September 06, 2012, Daniel Lezcano wrote:
> > > > > On 09/06/2012 10:04 PM, Rafael J. Wysocki wrote:
> > > > > > On Thursday, September 06, 2012, Daniel Lezcano wrote:
> > > > > > > On 09/06/2012 09:54 AM, Daniel Lezcano wrote:
> > > > > > > I fall into this issue because NETCONSOLE is set, disabling it
> > > > > > > allowed
> > > > > > > me to go further.
> > > > > > >
> > > > > > > Unfortunately I am facing to some random freeze on the system which
> > > > > > > seems to be related to CONFIG_NO_HZ=y and CONFIG_CPU_IDLE=y.
> > > > > > >
> > > > > > > Disabling one of them, make the freezes to disappear.
> > > > > > >
> > > > > > > Is it a known issue ?
> > > > > > Well, there are systems having problems with this configuration,
> > > > > > but they
> > > > > > should be exceptional.  What system is that?
> > > > > It is a laptop T61p with a Core 2 Duo T9500. Nothing exceptional I
> > > > > believe. Maybe someone got the same issue ?
> > > > Is it a regression for you?
> > > Yes, I think so. The issue appears between v3.5 and v3.6-rc1.
> > >
> > > It is not easy to reproduce but after taking some time to dig, it seems
> > > to appear with this commit:
> > >
> > > 1e75fa8be9fb61e1af46b5b3b176347a4c958ca1 is the first bad commit
> > > commit 1e75fa8be9fb61e1af46b5b3b176347a4c958ca1
> > > Author: John Stultz <john.stultz@xxxxxxxxxx>
> > > Date:   Fri Jul 13 01:21:53 2012 -0400
> > >
> > >       time: Condense timekeeper.xtime into xtime_sec
> > >
> > >       The timekeeper struct has a xtime_nsec, which keeps the
> > >       sub-nanosecond remainder.  This ends up being somewhat
> > >       duplicative of the timekeeper.xtime.tv_nsec value, and we
> > >       have to do extra work to keep them apart, copying the full
> > >       nsec portion out and back in over and over.
> > >
> > >       This patch simplifies some of the logic by taking the timekeeper
> > >       xtime value and splitting it into timekeeper.xtime_sec and
> > >       reuses the timekeeper.xtime_nsec for the sub-second portion
> > >       (stored in higher res shifted nanoseconds).
> > >
> > >       This simplifies some of the accumulation logic. And will
> > >       allow for more accurate timekeeping once the vsyscall code
> > >       is updated to use the shifted nanosecond remainder.
> > >
> > >       Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
> > >       Reviewed-by: Ingo Molnar <mingo@xxxxxxxxxx>
> > >       Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> > >       Cc: Richard Cochran <richardcochran@xxxxxxxxx>
> > >       Cc: Prarit Bhargava <prarit@xxxxxxxxxx>
> > >       Link:
> > > http://lkml.kernel.org/r/1342156917-25092-5-git-send-email-john.stultz@xxxxxxxxxx
> > >
> > >       Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > >
> > > :040000 040000 4d6541ac1f6075d7adee1eef494b31a0cbda0934
> > > dc5708bc738af695f092bf822809b13a1da104b6 M    kernel
> > >
> > > How to reproduce: with a laptop T61p, with a Core 2 Duo. I boot the
> > > kernel in busybox and wait some minutes before writing something in the
> > > console. At this moment, nothing appears to the console but the
> > > characters are echo'ed several seconds later (could be 1, 5, or 10 secs
> > > or more).
> > >
> > > That happens when CONFIG_CPU_IDLE and CONFIG_NO_HZ are set. Disabling
> > > one of them, the issue does not appear.
> > Thanks for bisecting this down and the heads up!
> >
> > Right off I can't see what might be causing this.  Bunch of questions:
> >
> > Is this a 32 or 64 bit kernel?
> It is a 32 bit kernel.
Thanks for your answers! Has this has been seen on 3.6-rc4+ kernels? 
There were a few casting fixes that landed in 3.6-rc4 that would affect 
32bit systems.
In the meantime, I'll try to reproduce on my T61. If you could send me 
your .config, I'd appreciate it.
thanks!
-john


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