[PATCH 1/2] iproute2: Improve list add.

[PATCH 1/2] iproute2: Improve list add.

[Pravin B Shelar]

ip command reads entire list of devices on every flush command.
While adding device record to list is does list traversal O(n).
This is time consuming for large batch commands.
Following patch improves list add operation to O(1).

Reported-by: Justin Pettit <jpettit@nicira.com>
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
---
 ip/ipaddress.c |   16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/ip/ipaddress.c b/ip/ipaddress.c
index 9ab65ec..7080c41 100644
--- a/ip/ipaddress.c
+++ b/ip/ipaddress.c
@@ -714,6 +714,7 @@ int print_addrinfo_secondary(const struct sockaddr_nl *who, struct nlmsghdr *n,
 struct nlmsg_list
 {
 	struct nlmsg_list *next;
+	struct nlmsg_list *last;
 	struct nlmsghdr	  h;
 };
 
@@ -744,17 +745,24 @@ static int store_nlmsg(const struct sockaddr_nl *who, struct nlmsghdr *n,
 {
 	struct nlmsg_list **linfo = (struct nlmsg_list**)arg;
 	struct nlmsg_list *h;
-	struct nlmsg_list **lp;
 
-	h = malloc(n->nlmsg_len+sizeof(void*));
+	h = malloc(n->nlmsg_len+sizeof(void*)+sizeof(void*));
 	if (h == NULL)
 		return -1;
 
 	memcpy(&h->h, n, n->nlmsg_len);
 	h->next = NULL;
 
-	for (lp = linfo; *lp; lp = &(*lp)->next) /* NOTHING */;
-	*lp = h;
+	if (!*linfo) {
+		/* First element. */
+		h->last = h;
+		*linfo = h;
+	} else {
+		struct nlmsg_list *last = (*linfo)->last;
+
+		last->next = h;
+		(*linfo)->last = h;
+	}
 
 	ll_remember_index(who, n, NULL);
 	return 0;
-- 
1.7.10

Re: [PATCH 1/2] iproute2: Improve list add.

[Stephen Hemminger]

On Tue, 22 May 2012 15:37:19 -0700
Pravin B Shelar <pshelar@nicira.com> wrote:

> ip command reads entire list of devices on every flush command.
> While adding device record to list is does list traversal O(n).
> This is time consuming for large batch commands.
> Following patch improves list add operation to O(1).
> 
> Reported-by: Justin Pettit <jpettit@nicira.com>
> Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
> ---
>  ip/ipaddress.c |   16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
> 

This no longer applies, after a similar patch I just accepted
from Eric.

commit 62e2e540919d31147165dabd35431c0649122c96
Author: Eric Dumazet <edumazet@google.com>
Date:   Sat Jun 9 13:55:55 2012 +0200

    ip: speedup ip link
    
    ip link has quadratic behavior because store_nlmsg()
    has a head list pointer and search the end of list.
    
    Provides a head/tail to cut time.
    
    Time with 128000 net devices, to do "ip link show dev xxx"
    
    Before: 2m3.594s
    After: 0m2.830s
    
    Signed-off-by: Eric Dumazet <edumazet@google.com>


If that doesn't fix your problem go ahead and resubmit.