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Re: [Xen-devel] Soft lockup/Time went backwards in latest unstable

On 26 Feb 2007, at 13:22, Keir Fraser wrote:

There were big changes to Linux's time handling between
2.6.16 and 2.6.18 so bugs may hav ebeen introduced while porting out own timer code. It might be worth diffing the file time-xen.c from working and non-working Linux kernels. It's weird that the failure mode is bad on the T60p yet noone else has reported this bug, nor has our testing reproduced
it. :-(

Some more information on the bug hunt in progress, in case anyone with more experience has any ideas:

* Changeset 13508 (i.e. the last one before the transition to a 2.6.17 kernel) fails in the same way as the current unstable, but it uses a kernel. * Changeset 13213 (which introduced the idle=poll option in the kernel when running on Xen) also fails with a kernel. * Changeset 13216 fails to boot at all (or, at least, locks up for >= 30 seconds on boot). * Changeset 13217 ("Make sure we always have a sensible idle function; this fixed problems") fails with time going backwards.
* Changeset 13212, however, works.

The only relevant changes between changesets 13212 and 13213 apply to the file linux-2.6-xen-sparse/arch/i386/kernel/process-xen.c (and the corresponding x86_64 file), to which a poll_idle() function has been added. I don't quite understand the significance of this, but could it be responsible for the bug that I'm seeing?


Derek Murray.

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