Re: [RFC PATCH v3 2/7] proc: Reduce cache miss in {snmp,netstat}_seq_show

Tue, 13 Sep 2016 22:59:36 -0700 

Hi Marcelo


On 9/13/16 2:57 AM, Marcelo wrote:

On Fri, Sep 09, 2016 at 02:33:57PM +0800, Jia He wrote:

This is to use the generic interface snmp_get_cpu_field{,64}_batch to
aggregate the data by going through all the items of each cpu sequentially.
Then snmp_seq_show and netstat_seq_show are split into 2 parts to avoid build
warning "the frame size" larger than 1024 on s390.

Yeah about that, did you test it with stack overflow detection?
These arrays can be quite large.

One more below..

Do you think it is acceptable if the stack usage is a little larger than 1024?
e.g. 1120
I can't find any other way to reduce the stack usage except use "static" before
unsigned long buff[TCP_MIB_MAX]

PS. sizeof buff is about TCP_MIB_MAX(116)*8=928
B.R.

Signed-off-by: Jia He <hejia...@gmail.com>
---
  net/ipv4/proc.c | 106 +++++++++++++++++++++++++++++++++++++++-----------------
  1 file changed, 74 insertions(+), 32 deletions(-)

diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
index 9f665b6..c6fc80e 100644
--- a/net/ipv4/proc.c
+++ b/net/ipv4/proc.c
@@ -46,6 +46,8 @@
  #include <net/sock.h>
  #include <net/raw.h>
+#define TCPUDP_MIB_MAX max_t(u32, UDP_MIB_MAX, TCP_MIB_MAX) 
+
  /*
   *    Report socket allocation statistics [m...@utu.fi]
   */
@@ -378,13 +380,15 @@ static void icmp_put(struct seq_file *seq)
  /*
   *    Called from the PROCfs module. This outputs /proc/net/snmp.
   */
-static int snmp_seq_show(struct seq_file *seq, void *v)
+static int snmp_seq_show_ipstats(struct seq_file *seq, void *v)
  {
        int i;
+       u64 buff64[IPSTATS_MIB_MAX];
        struct net *net = seq->private;
- seq_puts(seq, "Ip: Forwarding DefaultTTL"); 
+       memset(buff64, 0, IPSTATS_MIB_MAX * sizeof(u64));
+ seq_puts(seq, "Ip: Forwarding DefaultTTL"); 
        for (i = 0; snmp4_ipstats_list[i].name != NULL; i++)
                seq_printf(seq, " %s", snmp4_ipstats_list[i].name);
@@ -393,57 +397,77 @@ static int snmp_seq_show(struct seq_file *seq, void *v) 
                   net->ipv4.sysctl_ip_default_ttl);
BUILD_BUG_ON(offsetof(struct ipstats_mib, mibs) != 0); 
+       snmp_get_cpu_field64_batch(buff64, snmp4_ipstats_list,
+                                  net->mib.ip_statistics,
+                                  offsetof(struct ipstats_mib, syncp));
        for (i = 0; snmp4_ipstats_list[i].name != NULL; i++)
-               seq_printf(seq, " %llu",
-                          snmp_fold_field64(net->mib.ip_statistics,
-                                            snmp4_ipstats_list[i].entry,
-                                            offsetof(struct ipstats_mib, 
syncp)));
+               seq_printf(seq, " %llu", buff64[i]);
- icmp_put(seq); /* RFC 2011 compatibility */ 
-       icmpmsg_put(seq);
+       return 0;
+}
+
+static int snmp_seq_show_tcp_udp(struct seq_file *seq, void *v)
+{
+       int i;
+       unsigned long buff[TCPUDP_MIB_MAX];
+       struct net *net = seq->private;
+
+       memset(buff, 0, TCPUDP_MIB_MAX * sizeof(unsigned long));
seq_puts(seq, "\nTcp:"); 
        for (i = 0; snmp4_tcp_list[i].name != NULL; i++)
                seq_printf(seq, " %s", snmp4_tcp_list[i].name);
seq_puts(seq, "\nTcp:"); 
+       snmp_get_cpu_field_batch(buff, snmp4_tcp_list,
+                                net->mib.tcp_statistics);
        for (i = 0; snmp4_tcp_list[i].name != NULL; i++) {
                /* MaxConn field is signed, RFC 2012 */
                if (snmp4_tcp_list[i].entry == TCP_MIB_MAXCONN)
-                       seq_printf(seq, " %ld",
-                                  snmp_fold_field(net->mib.tcp_statistics,
-                                                  snmp4_tcp_list[i].entry));
+                       seq_printf(seq, " %ld", buff[i]);
                else
-                       seq_printf(seq, " %lu",
-                                  snmp_fold_field(net->mib.tcp_statistics,
-                                                  snmp4_tcp_list[i].entry));
+                       seq_printf(seq, " %lu", buff[i]);
        }
+ memset(buff, 0, TCPUDP_MIB_MAX * sizeof(unsigned long)); 
+
+       snmp_get_cpu_field_batch(buff, snmp4_udp_list,
+                                net->mib.udp_statistics);
        seq_puts(seq, "\nUdp:");
        for (i = 0; snmp4_udp_list[i].name != NULL; i++)
                seq_printf(seq, " %s", snmp4_udp_list[i].name);
-
        seq_puts(seq, "\nUdp:");
        for (i = 0; snmp4_udp_list[i].name != NULL; i++)
-               seq_printf(seq, " %lu",
-                          snmp_fold_field(net->mib.udp_statistics,
-                                          snmp4_udp_list[i].entry));
+               seq_printf(seq, " %lu", buff[i]);
+
+       memset(buff, 0, TCPUDP_MIB_MAX * sizeof(unsigned long));
/* the UDP and UDP-Lite MIBs are the same */ 
        seq_puts(seq, "\nUdpLite:");
+       snmp_get_cpu_field_batch(buff, snmp4_udp_list,
+                                net->mib.udplite_statistics);
        for (i = 0; snmp4_udp_list[i].name != NULL; i++)
                seq_printf(seq, " %s", snmp4_udp_list[i].name);
-
        seq_puts(seq, "\nUdpLite:");
        for (i = 0; snmp4_udp_list[i].name != NULL; i++)
-               seq_printf(seq, " %lu",
-                          snmp_fold_field(net->mib.udplite_statistics,
-                                          snmp4_udp_list[i].entry));
+               seq_printf(seq, " %lu", buff[i]);
seq_putc(seq, '\n'); 
        return 0;
  }
+static int snmp_seq_show(struct seq_file *seq, void *v) 
+{
+       snmp_seq_show_ipstats(seq, v);
+
+       icmp_put(seq);  /* RFC 2011 compatibility */
+       icmpmsg_put(seq);
+
+       snmp_seq_show_tcp_udp(seq, v);
+
+       return 0;
+}
+
  static int snmp_seq_open(struct inode *inode, struct file *file)
  {
        return single_open_net(inode, file, snmp_seq_show);
@@ -457,41 +481,59 @@ static const struct file_operations snmp_seq_fops = {
        .release = single_release_net,
  };
- 
-
  /*
   *    Output /proc/net/netstat
   */
-static int netstat_seq_show(struct seq_file *seq, void *v)
+static int netstat_seq_show_tcpext(struct seq_file *seq, void *v)
  {
        int i;
+       unsigned long buff[LINUX_MIB_MAX];
        struct net *net = seq->private;
+ memset(buff, 0, sizeof(unsigned long) * LINUX_MIB_MAX); 
+
        seq_puts(seq, "TcpExt:");
        for (i = 0; snmp4_net_list[i].name != NULL; i++)
                seq_printf(seq, " %s", snmp4_net_list[i].name);
seq_puts(seq, "\nTcpExt:"); 
+       snmp_get_cpu_field_batch(buff, snmp4_net_list,
+                                net->mib.net_statistics);
        for (i = 0; snmp4_net_list[i].name != NULL; i++)
-               seq_printf(seq, " %lu",
-                          snmp_fold_field(net->mib.net_statistics,
-                                          snmp4_net_list[i].entry));
+               seq_printf(seq, " %lu", buff[i]);
+
+       return 0;
+}
+
+static int netstat_seq_show_ipext(struct seq_file *seq, void *v)
+{
+       int i;
+       u64 buff64[IPSTATS_MIB_MAX];
+       struct net *net = seq->private;
seq_puts(seq, "\nIpExt:"); 
        for (i = 0; snmp4_ipextstats_list[i].name != NULL; i++)
                seq_printf(seq, " %s", snmp4_ipextstats_list[i].name);
seq_puts(seq, "\nIpExt:"); 
You're missing a memset() call here.


+       snmp_get_cpu_field64_batch(buff64, snmp4_ipextstats_list,
+                                  net->mib.ip_statistics,
+                                  offsetof(struct ipstats_mib, syncp));
        for (i = 0; snmp4_ipextstats_list[i].name != NULL; i++)
-               seq_printf(seq, " %llu",
-                          snmp_fold_field64(net->mib.ip_statistics,
-                                            snmp4_ipextstats_list[i].entry,
-                                            offsetof(struct ipstats_mib, 
syncp)));
+               seq_printf(seq, " %llu", buff64[i]);
seq_putc(seq, '\n'); 
        return 0;
  }
+static int netstat_seq_show(struct seq_file *seq, void *v) 
+{
+       netstat_seq_show_tcpext(seq, v);
+       netstat_seq_show_ipext(seq, v);
+
+       return 0;
+}
+
  static int netstat_seq_open(struct inode *inode, struct file *file)
  {
        return single_open_net(inode, file, netstat_seq_show);
--
1.8.3.1

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