Re: [PATCH, RFC] v4 scalable classic RCU implementation

[Manfred Spraul]

Paul E. McKenney wrote:
>   
> > That means an O(NR_CPUS) loop with disabled local interrupts :-(
> > Is that correct?
> >     
>
> With the definition of "O()" being the worst-case execution time, yes.
> But this worst case could only happen when the system was mostly idle,
> in which case the added overhead should not be too horribly bad.
No: "was mostly running cpu_idle()". A cpu_idle() cpu could execute lots 
of irqs and softirqs.
So the worst case would be a system with 1 cpu/node for reserved for irq 
handling.
The "idle" cpu would be always in no_hz mode, even though it might be 
100% busy handling irqs.
The remaning cpus might be 100% busy handling user space.

And every quiescent state will end up in that O(NR_CPUS) loop.

--
   Manfred
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