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/...

[Andre Oppermann]

On 24.10.2012 16:45, John Baldwin wrote:
> On Wednesday, October 24, 2012 10:34:34 am Attilio Rao wrote:
>> On Wed, Oct 24, 2012 at 3:05 PM, John Baldwin <jhb at freebsd.org> wrote:
>>> On Tuesday, October 23, 2012 7:20:04 pm Andre Oppermann wrote:
>>>> On 24.10.2012 00:15, mdf at FreeBSD.org wrote:
>>>>> On Tue, Oct 23, 2012 at 7:41 AM, Andre Oppermann <andre at 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;
>>
>> Unfortunately that doesn't work as I've verified with alc@ few months ago.
>> The __aligned() attribute only works with structures definition, not
>> objects declaration.
>
> Are you saying that the typedef doesn't (I expect it doesn't), or that this
> doesn't:
>
> struct mtx foo __aligned(CACHE_LINE_SIZE);

It has to be:

  struct mtx __aligned(CACHE_LINE_SIZE) foo;

doesn't it?  The gcc documentation isn't entirely clear to me.

-- 
Andre