LKML Archive on lore.kernel.org
 help / color / Atom feed
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
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
 
 /*

                 reply index

Thread overview: [no followups] expand[flat|nested]  mbox.gz  Atom feed

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20170309205322.GA1728@avx2 \
    --to=adobriyan@gmail.com \
    --cc=akpm@linux-foundation.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=rusty@rustcorp.com.au \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
	git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git
	git clone --mirror https://lore.kernel.org/lkml/9 lkml/git/9.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git