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From: John Baldwin <jhb@freebsd.org>
To: Andre Oppermann <andre@freebsd.org>
Subject: Re: svn commit: r241889 - in user/andre/tcp_workqueue/sys: arm/arm
 cddl/compat/opensolaris/kern cddl/contrib/opensolaris/uts/common/dtrace
 cddl/contrib/opensolaris/uts/common/fs/zfs ddb dev/acpica dev/...
Date: Wed, 24 Oct 2012 10:05:38 -0400
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 (bigwig.baldwin.cx); Wed, 24 Oct 2012 10:14:57 -0400 (EDT)
Cc: mdf@freebsd.org, src-committers@freebsd.org,
 Bruce Evans <brde@optusnet.com.au>, svn-src-user@freebsd.org
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On Tuesday, October 23, 2012 7:20:04 pm Andre Oppermann wrote:
> On 24.10.2012 00:15, mdf@FreeBSD.org wrote:
> > On Tue, Oct 23, 2012 at 7:41 AM, Andre Oppermann <andre@freebsd.org> wrote:
> >> Struct mtx and MTX_SYSINIT always occur as pair next to each other.
> >
> > That doesn't matter.  Language basics like variable definitions should
> > not be obscured by macros.  It either takes longer to figure out what
> > a variable is (because one needs to look up the definition of the
> > macro) or makes it almost impossible (because now e.g. cscope doesn't
> > know this is a variable definition.
> 
> Sigh, cscope doesn't expand macros?
> 
> Is there a way to do the cache line alignment in a sane way without
> littering __aligned(CACHE_LINE_SIZE) all over the place?

I was hoping to do something with an anonymous union or some such like:

union mtx_aligned {
	struct mtx;
	char[roundup2(sizeof(struct mtx), CACHE_LINE_SIZE)];
}

I don't know if there is a useful way to define an 'aligned mutex' type
that will transparently map to a 'struct mtx', e.g.:

typedef struct mtx __aligned(CACHE_LINE_SIZE) aligned_mtx_t;

-- 
John Baldwin