From: Andi Kleen <ak@suse.de>
To: Eric Dumazet <dada1@cosmosbay.com>
Cc: David Miller <davem@davemloft.net>,
mchan@broadcom.com, netdev@vger.kernel.org
Subject: Re: [PATCH] tg3 : avoid an expensive divide
Date: Wed, 7 Feb 2007 11:27:42 +0100 [thread overview]
Message-ID: <200702071127.42298.ak@suse.de> (raw)
In-Reply-To: <200702071056.04879.dada1@cosmosbay.com>
> Well, this could explain but unfortunatly I dont have this option set :
>
> # grep OPTIMIZE .config
> # CONFIG_CC_OPTIMIZE_FOR_SIZE is not set
>
> # gcc -v
> Using built-in specs.
> Target: x86_64-unknown-linux-gnu
> Configured with: ../gcc-4.1.1/configure --enable-languages=c,c++
Ah. Looking more closely the problem is different (sorry for the wrong
explanation earlier, it fit too well and it really happened elsewhere)
The code is
#define TG3_RX_RCB_RING_SIZE(tp) \
((tp->tg3_flags2 & TG3_FLG2_5705_PLUS) ? 512 : 1024)
...
sw_idx %= TG3_RX_RCB_RING_SIZE(tp);
The problem is that gcc doesn't rewrite the x % (cond ? const1 : const2) expression
to the more optimizable cond ? (x % const1 : x % const2). For the first it sees
a full variable division, for which div* is the best code to generate.
Your patch is probably correct or alternatively rewrite the expression
to the optimizable form by hand.
Arguably gcc should do this by itself. Perhaps file a gcc bug about this missing optimization.
-Andi
next prev parent reply other threads:[~2007-02-07 10:27 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-01-03 16:33 [PATCH/RFC 00/10] Transparent proxying patches version 4 KOVACS Krisztian
2007-01-03 16:34 ` [PATCH/RFC 01/10] Implement local diversion of IPv4 skbs KOVACS Krisztian
2007-01-10 6:46 ` Patrick McHardy
2007-01-10 9:31 ` Balazs Scheidler
2007-01-10 12:32 ` Patrick McHardy
2007-01-10 13:27 ` Ingo Oeser
2007-01-10 13:42 ` Patrick McHardy
2007-01-11 14:05 ` KOVACS Krisztian
2007-01-10 10:17 ` KOVACS Krisztian
2007-01-10 12:19 ` Patrick McHardy
2007-01-16 12:49 ` KOVACS Krisztian
2007-01-16 13:19 ` Patrick McHardy
2007-01-03 16:34 ` [PATCH/RFC 02/10] Port redirection support for TCP KOVACS Krisztian
2007-01-03 16:35 ` [PATCH/RFC 03/10] Don't do the TCP socket lookup if we already have one attached KOVACS Krisztian
2007-01-03 16:35 ` [PATCH/RFC 04/10] Don't do the UDP " KOVACS Krisztian
2007-01-03 16:36 ` [PATCH/RFC 05/10] Remove local address check on IP output KOVACS Krisztian
2007-01-10 6:47 ` Patrick McHardy
2007-01-10 10:01 ` KOVACS Krisztian
2007-02-06 14:36 ` IP_FREEBIND and CAP_NET_ADMIN (was: Re: [PATCH/RFC 05/10] Remove local address check on IP output) KOVACS Krisztian
2007-02-06 19:46 ` IP_FREEBIND and CAP_NET_ADMIN David Miller
2007-02-06 20:53 ` [PATCH] tg3 : avoid an expensive divide Eric Dumazet
2007-02-06 21:19 ` David Miller
2007-02-06 22:09 ` Michael Chan
2007-02-06 21:27 ` David Miller
2007-02-07 9:54 ` Andi Kleen
2007-02-07 9:45 ` David Miller
2007-02-07 9:56 ` Eric Dumazet
2007-02-07 10:27 ` Andi Kleen [this message]
2007-02-06 22:05 ` Michael Chan
2007-02-06 21:25 ` David Miller
2007-02-06 21:35 ` Eric Dumazet
2007-02-06 22:17 ` David Miller
2007-01-03 16:36 ` [PATCH/RFC 06/10] Create a tproxy flag in struct sk_buff KOVACS Krisztian
2007-01-03 16:37 ` [PATCH/RFC 07/10] Export UDP socket lookup function KOVACS Krisztian
2007-01-03 16:37 ` [PATCH/RFC 08/10] iptables tproxy table KOVACS Krisztian
2007-01-10 12:40 ` Patrick McHardy
2007-01-03 16:38 ` [PATCH/RFC 09/10] iptables TPROXY target KOVACS Krisztian
2007-01-10 12:45 ` Patrick McHardy
2007-01-03 16:38 ` [PATCH/RFC 10/10] iptables tproxy match KOVACS Krisztian
2007-01-03 17:23 ` [PATCH/RFC 00/10] Transparent proxying patches version 4 Evgeniy Polyakov
2007-01-08 20:30 ` KOVACS Krisztian
2007-01-03 19:33 ` Lennert Buytenhek
2007-01-04 12:13 ` KOVACS Krisztian
2007-01-04 12:16 ` Lennert Buytenhek
2007-01-07 14:11 ` Harald Welte
2007-01-07 16:11 ` Lennert Buytenhek
2007-01-07 23:58 ` Harald Welte
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