Re: [Xen-devel] [RFO] #2: removing a concurrency bottleneck

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 19/03/2009 17:52, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> wrote:

> I see two solutions: cascading or per-cpu.
> 
> In per-cpu, I would allocate at system initialization one
> pair of buffers for each cpu (question: num_present_cpus,
> num_online_cpus, or num_possible_cpus?).  Then no lock
> is required.

Just do this. A few pages per cpu is no significant overhead.

I suggest you allocate the buffers and store their addresses in your own
array of size NR_CPUS. You could do this from an __initcall function, or
from some other boot-time init function you have handy. The percpu stuff is
a bit fragile to large allocations (since we manually size the percpu
region!) and you will get no real benefit from it since we do not free/alloc
the percpu regions as cpus are onlined/offlined.

 -- keir



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