Messages in this thread | | | Date | 24 Mar 2006 04:47:38 +0100 | Date | Fri, 24 Mar 2006 04:47:38 +0100 | From | Andi Kleen <> | Subject | Re: 2.6.16-mm1 |
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> The above patch records the most-recent caller of local_irq_disable() in a > global variable, then prints that out in the lost-ticks handler. But how > do we know that the global didn't get overwritten between the most-recent > local_irq_enable() and the call to handle_lost_ticks()?
Because the overdue timer interrupt will trigger one instruction later.
> > I guess the code assumes that the local_irq_enable() will result in > insta-entry into the timer IRQ handler. Which is probably good enough, as > interrupts from other sources won't be pending most times.
Yes. Actually irq 0 has higher priority than most interrupts, but not all.
> > So why did we lose three ticks after __do_sortirq()'s local_irq_disable()? > Dunno.
It's a mistery. I put the patches in to trace a pattern.
But you're right they should at least be using per cpu variables instead of globals which can be corrupted by other CPUs.
> (Is there any point in do_softirq() doing local_irq_save() instead of > local_irq_disable()? __do_softirq() will unconditionally enable anyway..)
The interrupt handling in there is quite messy and has some other wards too. Could probably take a good cleanup. Problem is that it will need a lot of editing of architectures to do properly.
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