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From: Alexey Dobriyan <adobriyan@gmail.com>
To: akpm@linux-foundation.org
Cc: linux-kernel@vger.kernel.org
Subject: [PATCH] cpumask: make cpumask_next() out-of-line
Date: Fri, 25 Aug 2017 02:00:10 +0300
Message-ID: <20170824230010.GA1593@avx2> (raw)

Every for_each_XXX_cpu() invocation calls cpumask_next() which is an inline
function:

	static inline unsigned int cpumask_next(int n, const struct cpumask *srcp)
	{
	        /* -1 is a legal arg here. */
	        if (n != -1)
	                cpumask_check(n);
	        return find_next_bit(cpumask_bits(srcp), nr_cpumask_bits, n + 1);
	}

However!

find_next_bit() is regular out-of-line function which means "nr_cpu_ids" load and
increment happen at the caller resulting in a lot of bloat

x86_64 defconfig:
	add/remove: 3/0 grow/shrink: 8/373 up/down: 155/-5668 (-5513)
x86_64 allyesconfig-ish:
	add/remove: 3/1 grow/shrink: 57/634 up/down: 3515/-28177 (-24662) !!!

Some archs redefine find_next_bit() but it is OK:

	m68k		inline but SMP is not supported
	arm		out-of-line
	unicore32	out-of-line

Function call will happen anyway, so move load and increment into callee.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---

 include/linux/cpumask.h |   15 +--------------
 lib/cpumask.c           |   16 ++++++++++++++++
 2 files changed, 17 insertions(+), 14 deletions(-)

--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -178,20 +178,7 @@ static inline unsigned int cpumask_first(const struct cpumask *srcp)
 	return find_first_bit(cpumask_bits(srcp), nr_cpumask_bits);
 }
 
-/**
- * cpumask_next - get the next cpu in a cpumask
- * @n: the cpu prior to the place to search (ie. return will be > @n)
- * @srcp: the cpumask pointer
- *
- * Returns >= nr_cpu_ids if no further cpus set.
- */
-static inline unsigned int cpumask_next(int n, const struct cpumask *srcp)
-{
-	/* -1 is a legal arg here. */
-	if (n != -1)
-		cpumask_check(n);
-	return find_next_bit(cpumask_bits(srcp), nr_cpumask_bits, n+1);
-}
+unsigned int cpumask_next(int n, const struct cpumask *srcp);
 
 /**
  * cpumask_next_zero - get the next unset cpu in a cpumask
--- a/lib/cpumask.c
+++ b/lib/cpumask.c
@@ -6,6 +6,22 @@
 #include <linux/bootmem.h>
 
 /**
+ * cpumask_next - get the next cpu in a cpumask
+ * @n: the cpu prior to the place to search (ie. return will be > @n)
+ * @srcp: the cpumask pointer
+ *
+ * Returns >= nr_cpu_ids if no further cpus set.
+ */
+unsigned int cpumask_next(int n, const struct cpumask *srcp)
+{
+	/* -1 is a legal arg here. */
+	if (n != -1)
+		cpumask_check(n);
+	return find_next_bit(cpumask_bits(srcp), nr_cpumask_bits, n + 1);
+}
+EXPORT_SYMBOL(cpumask_next);
+
+/**
  * cpumask_next_and - get the next cpu in *src1p & *src2p
  * @n: the cpu prior to the place to search (ie. return will be > @n)
  * @src1p: the first cpumask pointer

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