Messages in this thread | | | Date | Mon, 08 Dec 2008 11:46:44 +0200 | From | Avi Kivity <> | Subject | Re: [PATCH 2/2] kvm: use cpumask_var_t for cpus_hardware_enabled |
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Rusty Russell wrote: >> This isn't on stack, so it isn't buying us anything. >> > > It's the CONFIG_NR_CPUS=4096 but nr_cpu_ids=4 case which we win using > dynamic allocation. Gotta love distribution kernels. > >
What does it buy? 4096/8 = 512 bytes statically allocated?
I understand passing things as pointers, but allocating everything dynamically is unCish.
>> Is the plan to drop cpumask_t? >> > > Yes. And undefine 'struct cpumask' if CONFIG_CPUMASK_OFFSTACK. That > will stop assignment and on-stack declarations for all but the most > determined. > > >> If so, we're penalizing non-stack users >> by forcing them to go through another pointer (and cacheline). >> > > Not quite. If !CONFIG_CPUMASK_OFFSTACK, cpumask_var_t == cpumask_t[1]. > Blame Linus :) >
Hm, is there a C trick which will error out when allocating something on the stack, but work when allocating statically? I can think of something to do the reverse, but that doesn't help.
Maybe a weak or visibility attribute? These don't make sense on function locals.
-- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.
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