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SubjectRe: cpu-2.5.64-1
On Sun, 16 Mar 2003 00:36:09 -0800, William Lee Irwin III wrote:
>> That was a bit too braindead of a translation, yes. But it is x86 arch
>> code so it shouldn't be that large of an issue for big MIPS boxen etc.
>> I'll search & replace for stuff of this kind and wipe it out anyway.

On Sun, Mar 16, 2003 at 08:19:31PM +1100, Keith Owens wrote:
> Good, it lets us optimize for 1/32/64/lots of cpus. NR_CPUS > 8 *
> sizeof(unsigned long) is the interesting case, it needs arrays.

Hmm. It shouldn't make a difference with respect to optimizing them.
My API passes transparently by reference:

#include <linux/bitmap.h>


struct cpumask
unsigned long mask[CPU_ARRAY_SIZE];

typedef struct cpumask cpumask_t;

#define cpu_set(cpu, map) set_bit(cpu, (map).mask)
#define cpu_clear(cpu, map) clear_bit(cpu, (map).mask)
#define cpu_isset(cpu, map) test_bit(cpu, (map).mask)
#define cpu_test_and_set(cpu, map) test_and_set_bit(cpu, (map).mask)
#define cpus_and(dst,src1,src2) bitmap_and((dst).mask, (src1).mask, (src2).mask, NR_CPUS)
#define cpus_or(dst,src1,src2) bitmap_or((dst).mask, (src1).mask, (src2).mask, NR_CPUS)
#define cpus_clear(map) bitmap_clear((map).mask, NR_CPUS)
#define cpus_equal(map1, map2) bitmap_equal((map1).mask, (map2).mask, NR_CPUS)
#define cpus_empty(map) (any_online_cpu(map) >= NR_CPUS)
#define first_cpu(map) find_first_bit((map).mask, NR_CPUS)
#define next_cpu(cpu, map) find_next_bit((map).mask, NR_CPUS, cpu)

i.e. the structures vaguely look like they're being passed by value and
I get the pointer to the start of the array with implicit decay.

Now the special case exploits the appearance of call by value:

#else /* !CONFIG_SMP */

typedef unsigned long cpumask_t;

#define any_online_cpu(map) ((map) != 0UL)
#define cpu_set(cpu, map) do { map |= 1UL << (cpu); } while (0)
#define cpu_clear(cpu, map) do { map &= ~(1UL << (cpu)); } while (0)
#define cpu_isset(cpu, map) ((map) & (1UL << (cpu)))
#define cpu_test_and_set(cpu, map) test_and_set_bit(cpu, &(map))
#define cpus_and(dst,src1,src2) do { dst = (src1) & (src2); } while (0)
#define cpus_or(dst,src1,src2) do { dst = (src1) | (src2); } while (0)
#define cpus_clear(map) do { map = 0UL; } while (0)
#define cpus_equal(map1, map2) ((map1) == (map2))
#define cpus_empty(map) ((map) != 0UL)
#define first_cpu(map) 0
#define next_cpu(cpu, map) NR_CPUS

... okay, a couple of minor fixups are needed for small-scale SMP, but
you get the idea. So basically the references to cpu_online_map don't
affect the UP/tinySMP special-casing b/c of the calling conventions
giving enough play to use either pointers (wrapped in structures) or
plain old unsigned longs.


#define first_cpu(map) __ffs(map)
#define next_cpu(cpu, map) __ffs((map) & ~((1UL < (cpu)) - 1))

*and* the plain old bugfix(!):

#define cpus_empty(map) ((map) == 0UL)

So mostly there isn't much to get excited about, but using
cpu_online_map directly doesn't appear to be a plus or a minus for my
strategy, if it in fact differs enough from any of the various others
of these posted before to be able to be called my own.

-- wli
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