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 16:34, 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:
>>> 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.

There is a huge amount of false cache line sharing in the .bss
section:

ffffffff81515980 B accept_mtx
ffffffff815159a0 B maxsockets
ffffffff815159a8 B socket_zone
ffffffff815159b0 B so_gencnt
ffffffff815159b8 B sysctl__kern_ipc_children

accept_mtx, socket_zone and so_gencnt are frequently accessed but
not related to each other and on different code path's.  There is
a lot of pointless cache dirtying going on.

Example randomly picked from "nm -n kernel.debug".

-- 
Andre