From: David Miller <davem@davemloft.net>
To: dada1@cosmosbay.com
Cc: mchan@broadcom.com, netdev@vger.kernel.org
Subject: Re: [PATCH] tg3 : avoid an expensive divide
Date: Tue, 06 Feb 2007 13:19:08 -0800 (PST) [thread overview]
Message-ID: <20070206.131908.13769204.davem@davemloft.net> (raw)
In-Reply-To: <45C8EAC4.9020803@cosmosbay.com>
From: Eric Dumazet <dada1@cosmosbay.com>
Date: Tue, 06 Feb 2007 21:53:24 +0100
> I am using gcc-4.1.1, so the following comment from drivers/net/tg3.c seems
> over-optimistic :
>
> /* Do not place this n-ring entries value into the tp struct itself,
> * we really want to expose these constants to GCC so that modulo et
> * al. operations are done with shifts and masks instead of with
> * hw multiply/modulo instructions. Another solution would be to
> * replace things like '% foo' with '& (foo - 1)'.
> */
> #define TG3_RX_RCB_RING_SIZE(tp) \
> ((tp->tg3_flags2 & TG3_FLG2_5705_PLUS) ? 512 : 1024)
Because I've seen gcc optimize this properly before (at least on
sparc64), it means that either:
1) There is a GCC bug where the properties of the constants
do not propagate.
2) GCC really thinks the divide is cheaper (code density vs.
cycle count tradeoffs etc.)
Anyways, we should probably apply your patch in any event.
Michael, any objections?
next prev parent reply other threads:[~2007-02-06 21:19 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 [this message]
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
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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