[RFC PATCH 2/6] proc: Reduce cache miss in snmp6_seq_show

[Jia He]

This patch exchanges the two loop for collecting the percpu
statistics data. This can reduce cache misses by going through
all the items of each cpu sequentially.

Signed-off-by: Jia He <hejia...@gmail.com>
---
 net/ipv6/proc.c | 47 ++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 36 insertions(+), 11 deletions(-)

diff --git a/net/ipv6/proc.c b/net/ipv6/proc.c
index 679253d0..c834646 100644
--- a/net/ipv6/proc.c
+++ b/net/ipv6/proc.c
@@ -30,6 +30,13 @@
 #include <net/transp_v6.h>
 #include <net/ipv6.h>
 
+#define MAX(a, b) ((u32)(a) >= (u32)(b) ? (a) : (b))
+
+#define MAX4(a, b, c, d) \
+       MAX(MAX(a, b), MAX(c, d))
+#define SNMP_MIB_MAX MAX4(UDP_MIB_MAX, TCP_MIB_MAX, \
+                       IPSTATS_MIB_MAX, ICMP_MIB_MAX)
+
 static int sockstat6_seq_show(struct seq_file *seq, void *v)
 {
        struct net *net = seq->private;
@@ -191,25 +198,43 @@ static void snmp6_seq_show_item(struct seq_file *seq, 
void __percpu *pcpumib,
                                atomic_long_t *smib,
                                const struct snmp_mib *itemlist)
 {
-       int i;
-       unsigned long val;
-
-       for (i = 0; itemlist[i].name; i++) {
-               val = pcpumib ?
-                       snmp_fold_field(pcpumib, itemlist[i].entry) :
-                       atomic_long_read(smib + itemlist[i].entry);
-               seq_printf(seq, "%-32s\t%lu\n", itemlist[i].name, val);
+       int i, c;
+       unsigned long buff[SNMP_MIB_MAX];
+
+       memset(buff, 0, sizeof(unsigned long) * SNMP_MIB_MAX);
+
+       if (pcpumib) {
+               for_each_possible_cpu(c)
+                       for (i = 0; itemlist[i].name; i++)
+                               buff[i] += snmp_get_cpu_field(pcpumib, c,
+                                                       itemlist[i].entry);
+               for (i = 0; itemlist[i].name; i++)
+                       seq_printf(seq, "%-32s\t%lu\n",
+                                  itemlist[i].name, buff[i]);
+       } else {
+               for (i = 0; itemlist[i].name; i++)
+                       seq_printf(seq, "%-32s\t%lu\n", itemlist[i].name,
+                                  atomic_long_read(smib + itemlist[i].entry));
        }
 }
 
 static void snmp6_seq_show_item64(struct seq_file *seq, void __percpu *mib,
                                  const struct snmp_mib *itemlist, size_t 
syncpoff)
 {
-       int i;
+       int i, c;
+       u64 buff[SNMP_MIB_MAX];
+
+       memset(buff, 0, sizeof(unsigned long) * SNMP_MIB_MAX);
 
+       for_each_possible_cpu(c) {
+               for (i = 0; itemlist[i].name; i++) {
+                       buff[i] += snmp_get_cpu_field64(mib, c,
+                                                       itemlist[i].entry,
+                                                       syncpoff);
+               }
+       }
        for (i = 0; itemlist[i].name; i++)
-               seq_printf(seq, "%-32s\t%llu\n", itemlist[i].name,
-                          snmp_fold_field64(mib, itemlist[i].entry, syncpoff));
+               seq_printf(seq, "%-32s\t%llu\n", itemlist[i].name, buff[i]);
 }
 
 static int snmp6_seq_show(struct seq_file *seq, void *v)
-- 
1.8.3.1