linux-kernel - Re: [PATCH net-next] net: avoid indirect calls in L4 checksum calculation

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Message-ID: <CAGnkfhxP0+WAaj4Kip+vuCphp7WnHUGJJMaEtj2xjUrnY253Zg@mail.gmail.com>
Date:   Wed, 29 May 2019 15:56:33 +0200
From:   Matteo Croce <mcroce@...hat.com>
To:     netdev <netdev@...r.kernel.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] net: avoid indirect calls in L4 checksum calculation

On Wed, May 29, 2019 at 1:58 AM Matteo Croce <mcroce@...hat.com> wrote:
>
> Commit 283c16a2dfd3 ("indirect call wrappers: helpers to speed-up
> indirect calls of builtin") introduces some macros to avoid doing
> indirect calls.
>
> Use these helpers to remove two indirect calls in the L4 checksum
> calculation for devices which don't have hardware support for it.
>
> As a test I generate packets with pktgen out to a dummy interface
> with HW checksumming disabled, to have the checksum calculated in
> every sent packet.
> The packet rate measured with an i7-6700K CPU and a single pktgen
> thread raised from 6143 to 6608 Kpps, an increase by 7.5%
>
> Suggested-by: Davide Caratti <dcaratti@...hat.com>
> Signed-off-by: Matteo Croce <mcroce@...hat.com>

I found a build error with CONFIG_LIBCRC32C=m:

ld: net/core/skbuff.o: in function `sctp_csum_update':
skbuff.c:(.text+0x2640): undefined reference to `crc32c'
ld: net/core/skbuff.o: in function `__skb_checksum':
(.text+0x2aba): undefined reference to `crc32c'
ld: (.text+0x2cf9): undefined reference to `crc32c'

I have two possible solutions for this:
- use INDIRECT_CALL_1 and leave the SCTP callback called by an indirect pointer
- use IS_BUILTIN(CONFIG_LIBCRC32C) around the sctp_csum_combine usage

I'm more toward the first one, which will also avoid the
net/sctp/checksum.h inclusion.

-- 
Matteo Croce
per aspera ad upstream