Rusty Russell wrote:
>
> In message <3C5669D6.B81E0B4@zip.com.au> you write:
> > Rusty Russell wrote:
> > >
> > > This patch introduces the __per_cpu_data tag for data, and the
> > > per_cpu() & this_cpu() macros to go with it.
> > >
> > > This allows us to get rid of all those special case structures
> > > springing up all over the place for CPU-local data.
> >
> > Am I missing something? smp_init() is called quite late in
> > the boot process, and if any code touches per-cpu data before
> > this, it'll get a null pointer deref, won't it?
>
> Yes. But for a large amount of code it doesn't matter, and most
> architectures don't know how many CPUs there are before smp_init().
> Of course, we could make it NR_CPUS...
I don't think there's a need. You can use .data.percpu directly
for the boot CPU, dynamically allocate storage for the others.
This actually saves one CPU's worth of memory :)
> Do you have an example where you want to use this before
> smp_boot_cpus()? If so, we can bite the bullet. Otherwise I'd prefer
> not to waste memory.
Well, the slab allocator uses per-CPU data, so with the current patch,
slab.c wouldn't be able to use per_cpu().
But if you use:
unsigned long __per_cpu_offset[NR_CPUS] = { (unsigned long *)&__per_cpu_start, };
Then each CPU has, at all times, a valid personal __per_cpu_offset[]
entry. The only restriction is that the boot CPU cannot
touch other CPU's per-cpu data before those CPUs are brought
up.
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This archive was generated by hypermail 2b29 : Thu Jan 31 2002 - 21:01:07 EST