linux-kernel - [PATCH v1 2/3] lib/cpumask: add inline cpumask_next

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Message-Id: <e2d40f6ab6758d11054c40272457d164f201d987.1660066581.git.sander@svanheule.net>
Date:   Tue,  9 Aug 2022 19:36:34 +0200
From:   Sander Vanheule <sander@...nheule.net>
To:     Yury Norov <yury.norov@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     linux-kernel@...r.kernel.org,
        Sander Vanheule <sander@...nheule.net>
Subject: [PATCH v1 2/3] lib/cpumask: add inline cpumask_next_wrap() for UP

In the uniprocessor case, cpumask_next_wrap() can be simplified, as the
number of valid argument combinations is limited:
    - 'start' can only be 0
    - 'n' can only be -1 or 0

The only valid CPU that can then be returned, if any, will be the first
one set in the provided 'mask'.

For NR_CPUS == 1, include/linux/cpumask.h now provides an inline
definition of cpumask_next_wrap(), which will conflict with the one
provided by lib/cpumask.c.  Make building of lib/cpumask.o again depend
on CONFIG_SMP=y (i.e. NR_CPUS > 1) to avoid the re-definition.

Suggested-by: Yury Norov <yury.norov@...il.com>
Signed-off-by: Sander Vanheule <sander@...nheule.net>
---
 include/linux/cpumask.h | 19 +++++++++++++++++++
 lib/Makefile            |  3 ++-
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index d8c2a40f8beb..bd047864c7ac 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -262,7 +262,26 @@ unsigned int cpumask_next_and(int n, const struct cpumask *src1p,
 		(cpu) = cpumask_next_zero((cpu), (mask)),	\
 		(cpu) < nr_cpu_ids;)
 
+#if NR_CPUS == 1
+static inline
+unsigned int cpumask_next_wrap(int n, const struct cpumask *mask, int start, bool wrap)
+{
+	cpumask_check(start);
+	if (n != -1)
+		cpumask_check(n);
+
+	/*
+	 * Return the first available CPU when wrapping, or when starting before cpu0,
+	 * since there is only one valid option.
+	 */
+	if (wrap && n >= 0)
+		return nr_cpumask_bits;
+
+	return cpumask_first(mask);
+}
+#else
 unsigned int __pure cpumask_next_wrap(int n, const struct cpumask *mask, int start, bool wrap);
+#endif
 
 /**
  * for_each_cpu_wrap - iterate over every cpu in a mask, starting at a specified location
diff --git a/lib/Makefile b/lib/Makefile
index c95212141928..5927d7fa0806 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -34,9 +34,10 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \
 	 is_single_threaded.o plist.o decompress.o kobject_uevent.o \
 	 earlycpio.o seq_buf.o siphash.o dec_and_lock.o \
 	 nmi_backtrace.o win_minmax.o memcat_p.o \
-	 buildid.o cpumask.o
+	 buildid.o
 
 lib-$(CONFIG_PRINTK) += dump_stack.o
+lib-$(CONFIG_SMP) += cpumask.o
 
 lib-y	+= kobject.o klist.o
 obj-y	+= lockref.o
-- 
2.37.1