linux-kernel - [PATCH 1/1] mm/percpu.c: simplify grouping cpu logic in pcpu_build_alloc

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Date:   Sat, 24 Sep 2016 02:15:09 +0800
From:   zijun_hu <zijun_hu@...o.com>
To:     Tejun Heo <tj@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     zijun_hu@....com, linux-mm@...ck.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        cl@...ux.com
Subject: [PATCH 1/1] mm/percpu.c: simplify grouping cpu logic in
 pcpu_build_alloc_info()

From: zijun_hu <zijun_hu@....com>

simplify grouping cpu logic in pcpu_build_alloc_info() to improve
readability and performance, it discards the goto statement too

for every possible cpu, decide whether it can share group id of any
lower index CPU, use the group id if so, otherwise a new group id
is allocated to it

Signed-off-by: zijun_hu <zijun_hu@....com>
---
 mm/percpu.c | 28 +++++++++++++++-------------
 1 file changed, 15 insertions(+), 13 deletions(-)

diff --git a/mm/percpu.c b/mm/percpu.c
index 9903830aaebb..fcaaac977954 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -1824,23 +1824,25 @@ static struct pcpu_alloc_info * __init pcpu_build_alloc_info(
 	max_upa = upa;
 
 	/* group cpus according to their proximity */
-	for_each_possible_cpu(cpu) {
-		group = 0;
-	next_group:
+	group = 0;
+	for_each_possible_cpu(cpu)
 		for_each_possible_cpu(tcpu) {
-			if (cpu == tcpu)
-				break;
-			if (group_map[tcpu] == group && cpu_distance_fn &&
-			    (cpu_distance_fn(cpu, tcpu) > LOCAL_DISTANCE ||
-			     cpu_distance_fn(tcpu, cpu) > LOCAL_DISTANCE)) {
+			if (tcpu == cpu) {
+				group_map[cpu] = group;
+				group_cnt[group] = 1;
 				group++;
-				nr_groups = max(nr_groups, group + 1);
-				goto next_group;
+				break;
+			}
+
+			if (!cpu_distance_fn ||
+			    (cpu_distance_fn(cpu, tcpu) == LOCAL_DISTANCE &&
+			     cpu_distance_fn(tcpu, cpu) == LOCAL_DISTANCE)) {
+				group_map[cpu] = group_map[tcpu];
+				group_cnt[group_map[cpu]]++;
+				break;
 			}
 		}
-		group_map[cpu] = group;
-		group_cnt[group]++;
-	}
+	nr_groups = group;
 
 	/*
 	 * Expand unit size until address space usage goes over 75%
-- 
1.9.1