x86: Add performance variants of cpumask operators

  * Increase performance for systems with large count NR_CPUS by limiting
    the range of the cpumask operators that loop over the bits in a cpumask_t
    variable.  This removes a large amount of wasted cpu cycles.

  * Add performance variants of the cpumask operators:

    int cpus_weight_nr(mask)	     Same using nr_cpu_ids instead of NR_CPUS
    int first_cpu_nr(mask)	     Number lowest set bit, or nr_cpu_ids
    int next_cpu_nr(cpu, mask)	     Next cpu past 'cpu', or nr_cpu_ids
    for_each_cpu_mask_nr(cpu, mask)  for-loop cpu over mask using nr_cpu_ids

  * Modify following to use performance variants:

    #define num_online_cpus()	cpus_weight_nr(cpu_online_map)
    #define num_possible_cpus()	cpus_weight_nr(cpu_possible_map)
    #define num_present_cpus()	cpus_weight_nr(cpu_present_map)

    #define for_each_possible_cpu(cpu) for_each_cpu_mask_nr((cpu), ...)
    #define for_each_online_cpu(cpu)   for_each_cpu_mask_nr((cpu), ...)
    #define for_each_present_cpu(cpu)  for_each_cpu_mask_nr((cpu), ...)

  * Comment added to include/linux/cpumask.h:

    Note: The alternate operations with the suffix "_nr" are used
	  to limit the range of the loop to nr_cpu_ids instead of
	  NR_CPUS when NR_CPUS > 64 for performance reasons.
	  If NR_CPUS is <= 64 then most assembler bitmask
	  operators execute faster with a constant range, so
	  the operator will continue to use NR_CPUS.

	  Another consideration is that nr_cpu_ids is initialized
	  to NR_CPUS and isn't lowered until the possible cpus are
	  discovered (including any disabled cpus).  So early uses
	  will span the entire range of NR_CPUS.

    (The net effect is that for systems with 64 or less CPU's there are no
     functional changes.)

For inclusion into sched-devel/latest tree.

Based on:
	git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
    +   sched-devel/latest  .../mingo/linux-2.6-sched-devel.git

Cc: Paul Jackson <pj@sgi.com>
Cc: Christoph Lameter <clameter@sgi.com>
Reviewed-by: Paul Jackson <pj@sgi.com>
Reviewed-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Mike Travis <travis@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 71 insertions, 30 deletions

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 5df3db58fcc6..b49472d1af84 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -17,6 +17,20 @@
  * For details of cpus_onto(), see bitmap_onto in lib/bitmap.c.
  * For details of cpus_fold(), see bitmap_fold in lib/bitmap.c.
  *
+ * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
+ * Note: The alternate operations with the suffix "_nr" are used
+ *       to limit the range of the loop to nr_cpu_ids instead of
+ *       NR_CPUS when NR_CPUS > 64 for performance reasons.
+ *       If NR_CPUS is <= 64 then most assembler bitmask
+ *       operators execute faster with a constant range, so
+ *       the operator will continue to use NR_CPUS.
+ *
+ *       Another consideration is that nr_cpu_ids is initialized
+ *       to NR_CPUS and isn't lowered until the possible cpus are
+ *       discovered (including any disabled cpus).  So early uses
+ *       will span the entire range of NR_CPUS.
+ * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
+ *
  * The available cpumask operations are:
  *
  * void cpu_set(cpu, mask)              turn on bit 'cpu' in mask
@@ -38,12 +52,14 @@
  * int cpus_empty(mask)                 Is mask empty (no bits sets)?
  * int cpus_full(mask)                  Is mask full (all bits sets)?
  * int cpus_weight(mask)                Hamming weigh - number of set bits
+ * int cpus_weight_nr(mask)             Same using nr_cpu_ids instead of NR_CPUS
  *
  * void cpus_shift_right(dst, src, n)   Shift right
  * void cpus_shift_left(dst, src, n)    Shift left
  *
  * int first_cpu(mask)                  Number lowest set bit, or NR_CPUS
  * int next_cpu(cpu, mask)              Next cpu past 'cpu', or NR_CPUS
+ * int next_cpu_nr(cpu, mask)           Next cpu past 'cpu', or nr_cpu_ids
  *
  * cpumask_t cpumask_of_cpu(cpu)        Return cpumask with bit 'cpu' set
  * CPU_MASK_ALL                         Initializer - all bits set
@@ -59,7 +75,8 @@
  * void cpus_onto(dst, orig, relmap)    *dst = orig relative to relmap
  * void cpus_fold(dst, orig, sz)        dst bits = orig bits mod sz
  *
- * for_each_cpu_mask(cpu, mask)         for-loop cpu over mask
+ * for_each_cpu_mask(cpu, mask)         for-loop cpu over mask using NR_CPUS
+ * for_each_cpu_mask_nr(cpu, mask)      for-loop cpu over mask using nr_cpu_ids
  *
  * int num_online_cpus()                Number of online CPUs
  * int num_possible_cpus()              Number of all possible CPUs
@@ -216,15 +233,6 @@ static inline void __cpus_shift_left(cpumask_t *dstp,
         bitmap_shift_left(dstp->bits, srcp->bits, n, nbits);
 }
 
-#ifdef CONFIG_SMP
-int __first_cpu(const cpumask_t *srcp);
-#define first_cpu(src) __first_cpu(&(src))
-int __next_cpu(int n, const cpumask_t *srcp);
-#define next_cpu(n, src) __next_cpu((n), &(src))
-#else
-#define first_cpu(src)          ({ (void)(src); 0; })
-#define next_cpu(n, src)        ({ (void)(src); 1; })
-#endif
 
 #ifdef CONFIG_HAVE_CPUMASK_OF_CPU_MAP
 extern cpumask_t *cpumask_of_cpu_map;
@@ -343,15 +351,48 @@ static inline void __cpus_fold(cpumask_t *dstp, const cpumask_t *origp,
         bitmap_fold(dstp->bits, origp->bits, sz, nbits);
 }
 
-#if NR_CPUS > 1
+#if NR_CPUS == 1
+
+#define nr_cpu_ids              1
+#define first_cpu(src)          ({ (void)(src); 0; })
+#define next_cpu(n, src)        ({ (void)(src); 1; })
+#define any_online_cpu(mask)    0
+#define for_each_cpu_mask(cpu, mask)    \
+        for ((cpu) = 0; (cpu) < 1; (cpu)++, (void)mask)
+
+#else /* NR_CPUS > 1 */
+
+extern int nr_cpu_ids;
+int __first_cpu(const cpumask_t *srcp);
+int __next_cpu(int n, const cpumask_t *srcp);
+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)))
-#else /* NR_CPUS == 1 */
-#define for_each_cpu_mask(cpu, mask)            \
-        for ((cpu) = 0; (cpu) < 1; (cpu)++, (void)mask)
-#endif /* NR_CPUS */
+#endif
+
+#if NR_CPUS <= 64
+
+#define next_cpu_nr(n, src)             next_cpu(n, src)
+#define cpus_weight_nr(cpumask)         cpus_weight(cpumask)
+#define for_each_cpu_mask_nr(cpu, mask) for_each_cpu_mask(cpu, mask)
+
+#else /* NR_CPUS > 64 */
+
+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)))
+
+#endif /* NR_CPUS > 64 */
 
 /*
  * The following particular system cpumasks and operations manage
@@ -414,9 +455,9 @@ extern cpumask_t cpu_online_map;
 extern cpumask_t cpu_present_map;
 
 #if NR_CPUS > 1
-#define num_online_cpus()       cpus_weight(cpu_online_map)
-#define num_possible_cpus()     cpus_weight(cpu_possible_map)
-#define num_present_cpus()      cpus_weight(cpu_present_map)
+#define num_online_cpus()       cpus_weight_nr(cpu_online_map)
+#define num_possible_cpus()     cpus_weight_nr(cpu_possible_map)
+#define num_present_cpus()      cpus_weight_nr(cpu_present_map)
 #define cpu_online(cpu)         cpu_isset((cpu), cpu_online_map)
 #define cpu_possible(cpu)       cpu_isset((cpu), cpu_possible_map)
 #define cpu_present(cpu)        cpu_isset((cpu), cpu_present_map)
@@ -431,17 +472,8 @@ extern cpumask_t cpu_present_map;
 
 #define cpu_is_offline(cpu)     unlikely(!cpu_online(cpu))
 
-#ifdef CONFIG_SMP
-extern int nr_cpu_ids;
-#define any_online_cpu(mask) __any_online_cpu(&(mask))
-int __any_online_cpu(const cpumask_t *mask);
-#else
-#define nr_cpu_ids                      1
-#define any_online_cpu(mask)            0
-#endif
-
-#define for_each_possible_cpu(cpu)  for_each_cpu_mask((cpu), cpu_possible_map)
-#define for_each_online_cpu(cpu)  for_each_cpu_mask((cpu), cpu_online_map)
-#define for_each_present_cpu(cpu) for_each_cpu_mask((cpu), cpu_present_map)
+#define for_each_possible_cpu(cpu) for_each_cpu_mask_nr((cpu), cpu_possible_map)
+#define for_each_online_cpu(cpu)   for_each_cpu_mask_nr((cpu), cpu_online_map)
+#define for_each_present_cpu(cpu)  for_each_cpu_mask_nr((cpu), cpu_present_map)
 
 #endif /* __LINUX_CPUMASK_H */
diff --git a/lib/cpumask.c b/lib/cpumask.c
index bb4f76d3c3e7..5f97dc25ef9c 100644
--- a/lib/cpumask.c
+++ b/lib/cpumask.c
@@ -15,6 +15,15 @@ int __next_cpu(int n, const cpumask_t *srcp)
 }
 EXPORT_SYMBOL(__next_cpu);
 
+#if NR_CPUS > 64
+int __next_cpu_nr(int n, const cpumask_t *srcp)
+{
+        return min_t(int, nr_cpu_ids,
+                                find_next_bit(srcp->bits, nr_cpu_ids, n+1));
+}
+EXPORT_SYMBOL(__next_cpu_nr);
+#endif
+
 int __any_online_cpu(const cpumask_t *mask)
 {
         int cpu;