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Subject[PATCH v5 2/5] cpumask: add UP optimised for_each_*_cpu versions
Date
On uniprocessor builds, the following loops will always run over a mask
that contains one enabled CPU (cpu0):
- for_each_possible_cpu
- for_each_online_cpu
- for_each_present_cpu

Provide uniprocessor-specific macros for these loops, that always run
exactly once, instead of just relying on for_each_cpu() to provide this
optimisation.

Signed-off-by: Sander Vanheule <sander@svanheule.net>
Acked-by: Yury Norov <yury.norov@gmail.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Marco Elver <elver@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Valentin Schneider <vschneid@redhat.com>
---
Changes since v4:
- Move patch forward in series
- Add Yury's Acked-by

include/linux/cpumask.h | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index fe29ac7cc469..533612770bc0 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -811,9 +811,16 @@ extern const DECLARE_BITMAP(cpu_all_bits, NR_CPUS);
/* First bits of cpu_bit_bitmap are in fact unset. */
#define cpu_none_mask to_cpumask(cpu_bit_bitmap[0])

+#if NR_CPUS == 1
+/* Uniprocessor: the possible/online/present masks are always "1" */
+#define for_each_possible_cpu(cpu) for ((cpu) = 0; (cpu) < 1; (cpu)++)
+#define for_each_online_cpu(cpu) for ((cpu) = 0; (cpu) < 1; (cpu)++)
+#define for_each_present_cpu(cpu) for ((cpu) = 0; (cpu) < 1; (cpu)++)
+#else
#define for_each_possible_cpu(cpu) for_each_cpu((cpu), cpu_possible_mask)
#define for_each_online_cpu(cpu) for_each_cpu((cpu), cpu_online_mask)
#define for_each_present_cpu(cpu) for_each_cpu((cpu), cpu_present_mask)
+#endif

/* Wrappers for arch boot code to manipulate normally-constant masks */
void init_cpu_present(const struct cpumask *src);
--
2.37.1
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