tcp_probe: avoid modulus operation and wrap fix

By rounding up the buffer size to power of 2, several expensive
modulus operations can be avoided.  This patch also solves a bug where
the gap need when ring gets full was not being accounted for.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 10 insertions, 9 deletions

diff --git a/net/ipv4/tcp_probe.c b/net/ipv4/tcp_probe.c
index bb110c5ce1d2..9bc805df95d2 100644
--- a/net/ipv4/tcp_probe.c
+++ b/net/ipv4/tcp_probe.c
@@ -39,9 +39,9 @@ static int port __read_mostly = 0;
 MODULE_PARM_DESC(port, "Port to match (0=all)");
 module_param(port, int, 0);
 
-static int bufsize __read_mostly = 4096;
+static unsigned int bufsize __read_mostly = 4096;
 MODULE_PARM_DESC(bufsize, "Log buffer size in packets (4096)");
-module_param(bufsize, int, 0);
+module_param(bufsize, uint, 0);
 
 static int full __read_mostly;
 MODULE_PARM_DESC(full, "Full log (1=every ack packet received,  0=only cwnd changes)");
@@ -75,12 +75,12 @@ static struct {
 
 static inline int tcp_probe_used(void)
 {
-        return (tcp_probe.head - tcp_probe.tail) % bufsize;
+        return (tcp_probe.head - tcp_probe.tail) & (bufsize - 1);
 }
 
 static inline int tcp_probe_avail(void)
 {
-        return bufsize - tcp_probe_used();
+        return bufsize - tcp_probe_used() - 1;
 }
 
 /*
@@ -116,7 +116,7 @@ static int jtcp_rcv_established(struct sock *sk, struct sk_buff *skb,
                         p->ssthresh = tcp_current_ssthresh(sk);
                         p->srtt = tp->srtt >> 3;
 
-                        tcp_probe.head = (tcp_probe.head + 1) % bufsize;
+                        tcp_probe.head = (tcp_probe.head + 1) & (bufsize - 1);
                 }
                 tcp_probe.lastcwnd = tp->snd_cwnd;
                 spin_unlock(&tcp_probe.lock);
@@ -149,7 +149,7 @@ static int tcpprobe_open(struct inode * inode, struct file * file)
 static int tcpprobe_sprint(char *tbuf, int n)
 {
         const struct tcp_log *p
-                = tcp_probe.log + tcp_probe.tail % bufsize;
+                = tcp_probe.log + tcp_probe.tail;
         struct timespec tv
                 = ktime_to_timespec(ktime_sub(p->tstamp, tcp_probe.start));
 
@@ -192,7 +192,7 @@ static ssize_t tcpprobe_read(struct file *file, char __user *buf,
                 width = tcpprobe_sprint(tbuf, sizeof(tbuf));
 
                 if (cnt + width < len)
-                        tcp_probe.tail = (tcp_probe.tail + 1) % bufsize;
+                        tcp_probe.tail = (tcp_probe.tail + 1) & (bufsize - 1);
 
                 spin_unlock_bh(&tcp_probe.lock);
 
@@ -222,9 +222,10 @@ static __init int tcpprobe_init(void)
         init_waitqueue_head(&tcp_probe.wait);
         spin_lock_init(&tcp_probe.lock);
 
-        if (bufsize < 0)
+        if (bufsize == 0)
                 return -EINVAL;
 
+        bufsize = roundup_pow_of_two(bufsize);
         tcp_probe.log = kcalloc(bufsize, sizeof(struct tcp_log), GFP_KERNEL);
         if (!tcp_probe.log)
                 goto err0;
@@ -236,7 +237,7 @@ static __init int tcpprobe_init(void)
         if (ret)
                 goto err1;
 
-        pr_info("TCP probe registered (port=%d)\n", port);
+        pr_info("TCP probe registered (port=%d) bufsize=%u\n", port, bufsize);
         return 0;
  err1:
         proc_net_remove(&init_net, procname);