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Date: Fri, 29 Jul 2022 09:01:19 +0200 From: Sander Vanheule <sander@...nheule.net> To: linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org> Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Brendan Higgins <brendanhiggins@...gle.com>, Dave Hansen <dave.hansen@...ux.intel.com>, David Gow <davidgow@...gle.com>, Borislav Petkov <bp@...en8.de>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "H . Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>, MaĆra Canal <mairacanal@...eup.net>, Marco Elver <elver@...gle.com>, Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>, Valentin Schneider <vschneid@...hat.com>, Yury Norov <yury.norov@...il.com>, Sander Vanheule <sander@...nheule.net> Subject: [PATCH v5 2/5] cpumask: add UP optimised for_each_*_cpu versions 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@...nheule.net> Acked-by: Yury Norov <yury.norov@...il.com> Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com> Cc: Borislav Petkov <bp@...en8.de> Cc: Dave Hansen <dave.hansen@...ux.intel.com> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org> Cc: "H. Peter Anvin" <hpa@...or.com> Cc: Ingo Molnar <mingo@...hat.com> Cc: Marco Elver <elver@...gle.com> Cc: Peter Zijlstra <peterz@...radead.org> Cc: Thomas Gleixner <tglx@...utronix.de> Cc: Valentin Schneider <vschneid@...hat.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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