[PATCH] cpumask: make "nr_cpumask_bits" unsigned

From: Alexey Dobriyan <adobriyan@gmail.com>
To: akpm@linux-foundation.org
Cc: linux-kernel@vger.kernel.org, rusty@rustcorp.com.au
Subject: [PATCH] cpumask: make "nr_cpumask_bits" unsigned
Date: Thu, 9 Mar 2017 23:53:22 +0300	[thread overview]
Message-ID: <20170309205322.GA1728@avx2> (raw)

Bit searching functions accept "unsigned long" indices
but "nr_cpumask_bits" is "int" which is signed, so inevitable
sign extensions occur on x86_64. Those MOVSX are #1 MOVSX bloat
by number of uses across whole kernel.

Change "nr_cpumask_bits" to unsigned, this number can't be negative
after all. It allows to do implicit zero-extension on x86_64
without MOVSX.

Change signed comparisons into unsigned comparisons where necessary.

Other uses looks fine because it is either argument passed to a function
or comparison is already unsigned.

Net win on allyesconfig type of kernel: ~2.8 KB (!)

	add/remove: 0/0 grow/shrink: 8/725 up/down: 93/-2926 (-2833)
	function                                     old     new   delta
	xen_exit_mmap                                691     735     +44
	qstat_read                                   426     440     +14
	__cpufreq_cooling_register                  1678    1687      +9
	trace_rb_cpu_prepare                         447     455      +8
	vermagic                                      54      60      +6
	nfp_driver_version                            54      60      +6
	rcu_torture_stats_print                     1147    1151      +4
	find_next_push_cpu                           267     269      +2
	xen_irq_resume                               961     960      -1
				...
	init_vp_index                                946     906     -40
	od_set_powersave_bias                        328     281     -47
	power_cpu_exit                               193     139     -54
	arch_show_interrupts                        3538    3484     -54
	select_idle_sibling                         1558    1471     -87
	Total: Before=158358910, After=158356077, chg -0.00%

Same arguments apply to "nr_cpu_ids" but I haven't yet found enough
courage to delve into this issue (and proper fix may require new type
"cpu_t" which is whole separate story).

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

 arch/mips/kernel/perf_event_mipsxx.c |    2 +-
 arch/s390/kernel/perf_cpum_sf.c      |    2 +-
 include/linux/cpumask.h              |    4 ++--
 3 files changed, 4 insertions(+), 4 deletions(-)

--- a/arch/mips/kernel/perf_event_mipsxx.c
+++ b/arch/mips/kernel/perf_event_mipsxx.c
@@ -618,7 +618,7 @@ static int mipspmu_event_init(struct perf_event *event)
 		return -ENOENT;
 	}
 
-	if (event->cpu >= nr_cpumask_bits ||
+	if ((unsigned int)event->cpu >= nr_cpumask_bits ||
 	    (event->cpu >= 0 && !cpu_online(event->cpu)))
 		return -ENODEV;
 
--- a/arch/s390/kernel/perf_cpum_sf.c
+++ b/arch/s390/kernel/perf_cpum_sf.c
@@ -823,7 +823,7 @@ static int cpumsf_pmu_event_init(struct perf_event *event)
 	}
 
 	/* Check online status of the CPU to which the event is pinned */
-	if (event->cpu >= nr_cpumask_bits ||
+	if ((unsigned int)event->cpu >= nr_cpumask_bits ||
 	    (event->cpu >= 0 && !cpu_online(event->cpu)))
 		return -ENODEV;
 
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -40,9 +40,9 @@ extern int nr_cpu_ids;
 #ifdef CONFIG_CPUMASK_OFFSTACK
 /* Assuming NR_CPUS is huge, a runtime limit is more efficient.  Also,
  * not all bits may be allocated. */
-#define nr_cpumask_bits	nr_cpu_ids
+#define nr_cpumask_bits	((unsigned int)nr_cpu_ids)
 #else
-#define nr_cpumask_bits	NR_CPUS
+#define nr_cpumask_bits	((unsigned int)NR_CPUS)
 #endif
 
 /*
