linux-kernel - Re: [PATCH akpm/next] lib: crc32: conditionally constify crc32 lookup table

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Message-Id: <20150102170828.3bb15c0a.akpm@linux-foundation.org>
Date:	Fri, 2 Jan 2015 17:08:28 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Daniel Borkmann <dborkman@...hat.com>
Cc:	linux-kernel@...r.kernel.org, Joe Mario <jmario@...hat.com>
Subject: Re: [PATCH akpm/next] lib: crc32: conditionally constify crc32
 lookup table

On Sat, 03 Jan 2015 01:12:43 +0100 Daniel Borkmann <dborkman@...hat.com> wrote:

> > Seems a lot of fuss.  Why are these tables cacheline aligned anyway?
> > To avoid one cache miss (most of the time, presumably) in a 16k table.
> > Pretty marginal benefit, I suspect.
> 
> I guess, it actually came in with the slice-by-8 algorithm (e.g. used
> in SCTP checksumming if no offloading is available) that was added back
> then, that is, commit 324eb0f17d9dc ("crc32: add slice-by-8 algorithm
> to existing code").

non-responsive ;)  By far the simplest solution is to remove the
cacheline alignment.

Are there other places where CC_HAVE_CONST_ALIGN can be used?  I'm seeing

z:/usr/src/linux-3.19-rc2> grep -r cacheline_aligned . | grep const
./arch/x86/um/sys_call_table_32.c:const sys_call_ptr_t sys_call_table[] __cacheline_aligned = {
./arch/x86/um/sys_call_table_64.c:const sys_call_ptr_t sys_call_table[] __cacheline_aligned = {
./include/net/netfilter/nf_tables.h:    const struct nft_set_ops        *ops ____cacheline_aligned;
./net/ethernet/eth.c:const struct header_ops eth_header_ops ____cacheline_aligned = {

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