[RFC PATCH v2 2/6] proc: Reduce cache miss in snmp6_seq_show

Jia He
2016-09-06T02:30:35Z

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 <hejianet@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