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Date: Fri, 23 Jan 2009 01:14:58 +0100
From: Eric Dumazet <dada1@...mosbay.com>
To: Vitaly Mayatskikh <v.mayatskih@...il.com>
CC: David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: speed regression in udp_lib_lport_inuse()
Vitaly Mayatskikh a écrit :
> At Thu, 22 Jan 2009 23:06:59 +0100, Eric Dumazet wrote:
>
>>> err = bind(s, (const struct sockaddr*)&sa, sizeof(sa));
>> Bug here, if bind() returns -1 (all ports are in use)
>
> Yeah, there was assert(), but the program drops to problems very soon,
> I was lazy to handle this situation correctly and just removed it ;)
>
>>> Thanks!
>> Hello Vitaly, thanks for this excellent report.
>>
>> Yes, current code is really not good when all ports are in use :
>>
>> We now have to scan 28232 [1] times long chains of 220 sockets.
>> Thats very long (but at least thread is preemptable)
>>
>> In the past (before patches), only one thread was allowed to run in kernel while scanning
>> udp port table (we had only one global lock udp_hash_lock protecting the whole udp table).
>
> Very true, my (older) kernel with udp_hash_lock just become totally
> unresponsive after running this test. .29-rc2 become jerky only, but
> still works.
>
>> This thread was faster because it was not slowed down by other threads.
>> (But the rwlock we used was responsible for starvations of writers if many UDP frames
>> were received)
>>
>>
>>
>> One way to solve the problem could be to use following :
>>
>> 1) Raising UDP_HTABLE_SIZE from 128 to 1024 to reduce average chain lengths.
>>
>> 2) In bind(0) algo, use rcu locking to find a possible usable port. All cpus can run in //, without
>> dirtying locks. Then lock the found chain and recheck port is available before using it.
>
> I think 2 is definitely better than 1, because 1 is not actually
> fixing anything, but postpones the problem slightly.
>
>> [1] replace 28232 by your actual /proc/sys/net/ipv4/ip_local_port_range values
>> 61000 - 32768 = 28232
>>
>> I will try to code a patch before this week end.
>
> Cool!
>
>> Thanks
>>
>> Note : I tried to use a mutex to force only one thread in bind(0) code but got no real speedup.
>> But it should help if you have a SMP machine, since only one cpu will be busy in bind(0)
>>
>
> You saved my time, I was thinking about trying mutexes also. Thanks :)
>
Could you try following patch ?
Thank you
[PATCH] udp: optimize bind(0) if many ports are in use
commit 9088c5609584684149f3fb5b065aa7f18dcb03ff
(udp: Improve port randomization) introduced a regression for UDP bind() syscall
to null port (getting a random port) in case lot of ports are already in use.
This is because we do about 28000 scans of very long chains (220 sockets per chain),
with many spin_lock_bh()/spin_unlock_bh() calls.
Fix this using a bitmap (64 bytes for current value of UDP_HTABLE_SIZE)
so that we scan chains at most once.
Instead of 250 ms per bind() call, we get after patch a time of 2.9 ms
Based on a report from Vitaly Mayatskikh
Reported-by: Vitaly Mayatskikh <v.mayatskih@...il.com>
Signed-off-by: Eric Dumazet <dada1@...mosbay.com>
---
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index cf5ab05..adbdbd8 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -120,8 +120,11 @@ EXPORT_SYMBOL(sysctl_udp_wmem_min);
atomic_t udp_memory_allocated;
EXPORT_SYMBOL(udp_memory_allocated);
+#define PORTS_PER_CHAIN (65536 / UDP_HTABLE_SIZE)
+
static int udp_lib_lport_inuse(struct net *net, __u16 num,
const struct udp_hslot *hslot,
+ unsigned long *bitmap,
struct sock *sk,
int (*saddr_comp)(const struct sock *sk1,
const struct sock *sk2))
@@ -132,12 +135,16 @@ static int udp_lib_lport_inuse(struct net *net, __u16 num,
sk_nulls_for_each(sk2, node, &hslot->head)
if (net_eq(sock_net(sk2), net) &&
sk2 != sk &&
- sk2->sk_hash == num &&
+ (bitmap || sk2->sk_hash == num) &&
(!sk2->sk_reuse || !sk->sk_reuse) &&
(!sk2->sk_bound_dev_if || !sk->sk_bound_dev_if
|| sk2->sk_bound_dev_if == sk->sk_bound_dev_if) &&
- (*saddr_comp)(sk, sk2))
- return 1;
+ (*saddr_comp)(sk, sk2)) {
+ if (bitmap)
+ __set_bit(sk2->sk_hash / UDP_HTABLE_SIZE, bitmap);
+ else
+ return 1;
+ }
return 0;
}
@@ -158,34 +165,44 @@ int udp_lib_get_port(struct sock *sk, unsigned short snum,
struct net *net = sock_net(sk);
if (!snum) {
- int low, high, remaining;
- unsigned rand;
+ int low, high;
+ unsigned rand, slotn, bias;
unsigned short first;
+ DECLARE_BITMAP(bitmap, PORTS_PER_CHAIN);
inet_get_local_port_range(&low, &high);
- remaining = (high - low) + 1;
rand = net_random();
- snum = first = rand % remaining + low;
- rand |= 1;
- for (;;) {
- hslot = &udptable->hash[udp_hashfn(net, snum)];
+ bias = rand;
+ rand = ((rand >> 16) | 1) * UDP_HTABLE_SIZE;
+ for (slotn = 0; slotn < UDP_HTABLE_SIZE; slotn++) {
+ first = slotn + bias;
+ hslot = &udptable->hash[udp_hashfn(net, first)];
+ bitmap_zero(bitmap, PORTS_PER_CHAIN);
spin_lock_bh(&hslot->lock);
- if (!udp_lib_lport_inuse(net, snum, hslot, sk, saddr_comp))
- break;
- spin_unlock_bh(&hslot->lock);
+ udp_lib_lport_inuse(net, snum, hslot, bitmap, sk, saddr_comp);
+
+ snum = first;
+ /*
+ * PORTS_PER_CHAIN loops, because snum is unsigned short
+ * and we add an odd multiple of UDP_HTABLE_SIZE
+ */
do {
- snum = snum + rand;
- } while (snum < low || snum > high);
- if (snum == first)
- goto fail;
+ if (low <= snum && snum <= high &&
+ !test_bit(snum / UDP_HTABLE_SIZE, bitmap))
+ goto found;
+ snum += rand;
+ } while (snum != first);
+ spin_unlock_bh(&hslot->lock);
}
+ goto fail;
} else {
hslot = &udptable->hash[udp_hashfn(net, snum)];
spin_lock_bh(&hslot->lock);
- if (udp_lib_lport_inuse(net, snum, hslot, sk, saddr_comp))
+ if (udp_lib_lport_inuse(net, snum, hslot, NULL, sk, saddr_comp))
goto fail_unlock;
}
+found:
inet_sk(sk)->num = snum;
sk->sk_hash = snum;
if (sk_unhashed(sk)) {
--
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