[PATCHv3] Make for_each_cpu_mask a bit smaller

From: Alexander van Heukelum
Date: Tue May 13 2008 - 05:30:29 EST


The for_each_cpu_mask loop is used quite often in the kernel. It
makes use of two functions: first_cpu and next_cpu. This patch
changes for_each_cpu_mask to use only the latter. Because next_cpu
finds the next eligible cpu _after_ the given one, the iteration
variable has to be initialized to -1 and next_cpu has to be
called with this value before the first iteration. An x86_64
defconfig kernel (from sched/latest) is about 2500 bytes smaller
with this patch applied:

text data bss dec hex filename
6222517 917952 749932 7890401 7865e1 vmlinux.orig
6219922 917952 749932 7887806 785bbe vmlinux

The same size reduction is seen for defconfig+MAXSMP

text data bss dec hex filename
6241772 2563968 1492716 10298456 9d2458 vmlinux.orig
6239211 2563968 1492716 10295895 9d1a57 vmlinux

Signed-off-by: Alexander van Heukelum <heukelum@xxxxxxxxxxx>

---

On Mon, May 12, 2008, Andreas Schwab wrote:
> > +#define for_each_cpu_mask(cpu, mask) \
> > + for ((cpu) = ~((typeof(cpu))0); \
>
> There is no need for such a complicated expression, -1 will work for
> every (arithmetic) type.

Indeed, thanks.

This version applies on top of sched/latest.

This version reuses the already-existing api next_cpu instead
of inventing a new one; initializing the iteration counter to
-1 was suggested by Matthew Wilcox. Now with a -1 instead of
an overly carefull ~((typeof(cpu))0). "-1" is properly sign-
extended even if cpu is u64 in a 32-bit environment.

Greetings,
Alexander

include/linux/cpumask.h | 16 ++++++++--------
1 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 73434e5..c24a556 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -377,10 +377,10 @@ int __any_online_cpu(const cpumask_t *mask);
#define first_cpu(src) __first_cpu(&(src))
#define next_cpu(n, src) __next_cpu((n), &(src))
#define any_online_cpu(mask) __any_online_cpu(&(mask))
-#define for_each_cpu_mask(cpu, mask) \
- for ((cpu) = first_cpu(mask); \
- (cpu) < NR_CPUS; \
- (cpu) = next_cpu((cpu), (mask)))
+#define for_each_cpu_mask(cpu, mask) \
+ for ((cpu) = -1; \
+ (cpu) = next_cpu((cpu), (mask)), \
+ (cpu) < NR_CPUS; )
#endif

#if NR_CPUS <= 64
@@ -394,10 +394,10 @@ int __any_online_cpu(const cpumask_t *mask);
int __next_cpu_nr(int n, const cpumask_t *srcp);
#define next_cpu_nr(n, src) __next_cpu_nr((n), &(src))
#define cpus_weight_nr(cpumask) __cpus_weight(&(cpumask), nr_cpu_ids)
-#define for_each_cpu_mask_nr(cpu, mask) \
- for ((cpu) = first_cpu(mask); \
- (cpu) < nr_cpu_ids; \
- (cpu) = next_cpu_nr((cpu), (mask)))
+#define for_each_cpu_mask_nr(cpu, mask) \
+ for ((cpu) = -1; \
+ (cpu) = next_cpu_nr((cpu), (mask)), \
+ (cpu) < nr_cpu_ids; )

#endif /* NR_CPUS > 64 */

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