From: Eric Dumazet <dada1@cosmosbay•com>
To: Eric Dumazet <dada1@cosmosbay•com>
Cc: Thomas Graf <tgraf@suug•ch>,
"David S. Miller" <davem@davemloft•net>,
netdev@oss•sgi.com
Subject: Re: [PATCH] loop unrolling in net/sched/sch_generic.c
Date: Wed, 06 Jul 2005 02:53:24 +0200 [thread overview]
Message-ID: <42CB2B84.50702@cosmosbay.com> (raw)
In-Reply-To: <42CB2698.2080904@cosmosbay.com>
Eric Dumazet a écrit :
>
>
> Maybe we can rewrite the whole thing without branches, examining prio
> from PFIFO_FAST_BANDS-1 down to 0, at least for modern cpu with
> conditional mov (cmov)
>
> struct sk_buff_head *best = NULL;
> struct sk_buff_head *list = qdisc_priv(qdisc)+PFIFO_FAST_BANDS-1;
> if (skb_queue_empty(list)) best = list ;
> list--;
> if (skb_queue_empty(list)) best = list ;
> list--;
> if (skb_queue_empty(list)) best = list ;
> if (best != NULL) {
> qdisc->q.qlen--;
> return __qdisc_dequeue_head(qdisc, best);
> }
>
> This version should have one branch.
> I will test this after some sleep :)
> See you
> Eric
>
>
(Sorry, still using 2.6.12, but the idea remains)
static struct sk_buff *
pfifo_fast_dequeue(struct Qdisc* qdisc)
{
struct sk_buff_head *list = qdisc_priv(qdisc);
struct sk_buff_head *best = NULL;
list += 2;
if (!skb_queue_empty(list))
best = list;
list--;
if (!skb_queue_empty(list))
best = list;
list--;
if (!skb_queue_empty(list))
best = list;
if (best) {
qdisc->q.qlen--;
return __skb_dequeue(best);
}
return NULL;
}
At least the compiler output seems promising :
0000000000000550 <pfifo_fast_dequeue>:
550: 48 8d 97 f0 00 00 00 lea 0xf0(%rdi),%rdx
557: 31 c9 xor %ecx,%ecx
559: 48 8d 87 c0 00 00 00 lea 0xc0(%rdi),%rax
560: 48 39 97 f0 00 00 00 cmp %rdx,0xf0(%rdi)
567: 48 0f 45 ca cmovne %rdx,%rcx
56b: 48 8d 97 d8 00 00 00 lea 0xd8(%rdi),%rdx
572: 48 39 97 d8 00 00 00 cmp %rdx,0xd8(%rdi)
579: 48 0f 45 ca cmovne %rdx,%rcx
57d: 48 39 87 c0 00 00 00 cmp %rax,0xc0(%rdi)
584: 48 0f 45 c8 cmovne %rax,%rcx
588: 31 c0 xor %eax,%eax
58a: 48 85 c9 test %rcx,%rcx
58d: 74 32 je 5c1 <pfifo_fast_dequeue+0x71> // one conditional branch
58f: ff 4f 40 decl 0x40(%rdi)
592: 48 8b 11 mov (%rcx),%rdx
595: 48 39 ca cmp %rcx,%rdx
598: 74 27 je 5c1 <pfifo_fast_dequeue+0x71> // never taken branch : always predicted OK
59a: 48 89 d0 mov %rdx,%rax
59d: 48 8b 12 mov (%rdx),%rdx
5a0: ff 49 10 decl 0x10(%rcx)
5a3: 48 c7 40 10 00 00 00 movq $0x0,0x10(%rax)
5aa: 00
5ab: 48 89 4a 08 mov %rcx,0x8(%rdx)
5af: 48 89 11 mov %rdx,(%rcx)
5b2: 48 c7 40 08 00 00 00 movq $0x0,0x8(%rax)
5b9: 00
5ba: 48 c7 00 00 00 00 00 movq $0x0,(%rax)
5c1: 90 nop
5c2: c3 retq
I Will post tomorrow some profiling results.
Eric
next prev parent reply other threads:[~2005-07-06 0:53 UTC|newest]
Thread overview: 64+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-05-11 21:15 [TG3]: Add hw coalescing infrastructure David S. Miller
2005-05-11 21:17 ` Michael Chan
2005-05-12 2:28 ` David S. Miller
2005-05-12 7:53 ` Robert Olsson
2005-06-22 15:25 ` [TG3]: About " Eric Dumazet
2005-06-22 19:03 ` Michael Chan
2005-07-04 21:22 ` Eric Dumazet
2005-07-04 21:26 ` David S. Miller
2005-07-04 21:39 ` Eric Dumazet
2005-07-04 21:49 ` David S. Miller
2005-07-04 22:31 ` Eric Dumazet
2005-07-04 22:47 ` David S. Miller
2005-07-04 22:55 ` Eric Dumazet
2005-07-04 22:57 ` Eric Dumazet
2005-07-04 23:01 ` David S. Miller
2005-07-05 7:38 ` [PATCH] loop unrolling in net/sched/sch_generic.c Eric Dumazet
2005-07-05 11:51 ` Thomas Graf
2005-07-05 12:03 ` Thomas Graf
2005-07-05 13:04 ` Eric Dumazet
2005-07-05 13:48 ` Thomas Graf
2005-07-05 15:58 ` Eric Dumazet
2005-07-05 17:34 ` Thomas Graf
2005-07-05 21:22 ` David S. Miller
2005-07-05 21:33 ` Thomas Graf
2005-07-05 21:35 ` David S. Miller
2005-07-05 23:16 ` Eric Dumazet
2005-07-05 23:41 ` Thomas Graf
2005-07-05 23:45 ` David S. Miller
2005-07-05 23:55 ` Thomas Graf
2005-07-06 0:32 ` Eric Dumazet
2005-07-06 0:51 ` Thomas Graf
2005-07-06 1:04 ` Eric Dumazet
2005-07-06 1:07 ` Thomas Graf
2005-07-06 0:53 ` Eric Dumazet [this message]
2005-07-06 1:02 ` Thomas Graf
2005-07-06 1:09 ` Eric Dumazet
2005-07-06 12:42 ` Thomas Graf
2005-07-07 21:17 ` David S. Miller
2005-07-07 21:34 ` Thomas Graf
2005-07-07 22:24 ` David S. Miller
[not found] ` <42CE22CE.7030902@cosmosbay.com>
2005-07-08 7:30 ` David S. Miller
2005-07-08 8:19 ` Eric Dumazet
2005-07-08 11:08 ` Arnaldo Carvalho de Melo
2005-07-12 4:02 ` David S. Miller
2005-07-05 21:26 ` David S. Miller
2005-07-28 15:52 ` [PATCH] Add prefetches in net/ipv4/route.c Eric Dumazet
2005-07-28 19:39 ` David S. Miller
2005-07-28 20:56 ` Eric Dumazet
2005-07-28 20:58 ` David S. Miller
2005-07-28 21:24 ` Eric Dumazet
2005-07-28 22:44 ` David S. Miller
2005-07-29 14:50 ` Robert Olsson
2005-07-29 17:06 ` Rick Jones
2005-07-29 17:44 ` Robert Olsson
2005-07-29 17:57 ` Eric Dumazet
2005-07-29 18:25 ` Rick Jones
2005-07-31 3:52 ` David S. Miller
[not found] ` <42EDDA50.4010405@cosmosbay.com>
2005-08-01 15:39 ` David S. Miller
2005-07-31 3:51 ` David S. Miller
2005-07-31 3:44 ` David S. Miller
2005-07-04 23:00 ` [TG3]: About hw coalescing infrastructure David S. Miller
2005-07-05 16:14 ` Eric Dumazet
2005-07-04 22:47 ` Eric Dumazet
[not found] <C925F8B43D79CC49ACD0601FB68FF50C045E0FB0@orsmsx408>
2005-07-07 22:30 ` [PATCH] loop unrolling in net/sched/sch_generic.c David S. Miller
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