Date: Mon, 23 Apr 2012 19:26:54 +0800 From: Fengwei yin <yfw.bsd@gmail.com> To: Slawa Olhovchenkov <slw@zxy.spb.ru> Cc: jack.ren@intel.com, freebsd-threads@freebsd.org Subject: Re: About the memory barrier in BSD libc Message-ID: <CAPHpMukLUeetSKpH2oiKJQ3ML_PFHEi6a0hK3_Ery=LX1YEd3g@mail.gmail.com> In-Reply-To: <20120423094043.GS32749@zxy.spb.ru> References: <CAPHpMu=DOGQ=TuFeYH7bH8hVwteT4Q3k67-mvoOFob6P3Y506w@mail.gmail.com> <20120423084120.GD76983@zxy.spb.ru> <CAPHpMu=kCwhf1RV_sYBDWDPL8368YTMLXge4L_g_F4AkTX1H5g@mail.gmail.com> <20120423094043.GS32749@zxy.spb.ru>
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On Mon, Apr 23, 2012 at 5:40 PM, Slawa Olhovchenkov <slw@zxy.spb.ru> wrote:
> On Mon, Apr 23, 2012 at 05:32:24PM +0800, Fengwei yin wrote:
>
>> On Mon, Apr 23, 2012 at 4:41 PM, Slawa Olhovchenkov <slw@zxy.spb.ru> wro=
te:
>> > On Mon, Apr 23, 2012 at 02:56:03PM +0800, Fengwei yin wrote:
>> >
>> >> Hi list,
>> >> If this is not correct question on the list, please let me know and
>> >> sorry for noise.
>> >>
>> >> I have a question regarding the BSD libc for SMP arch. I didn't see
>> >> memory barrier used in libc.
>> >> How can we make sure it's safe on SMP arch?
>> >
>> > /usr/include/machine/atomic.h:
>> >
>> > #define mb() =A0 =A0__asm __volatile("lock; addl $0,(%%esp)" : : : "me=
mory")
>> > #define wmb() =A0 __asm __volatile("lock; addl $0,(%%esp)" : : : "memo=
ry")
>> > #define rmb() =A0 __asm __volatile("lock; addl $0,(%%esp)" : : : "memo=
ry")
>> >
>>
>> Thanks for the information. But it looks no body use it in libc.
>
> I think no body in libc need memory barrier: libc don't work with
> peripheral, for atomic opertions used different macros.
If we check the usage of __sinit(), it is a typical singleton pattern which
needs memory barrier to make sure no potential SMP issue.
Or did I miss something here?
Regards
Yin, Fengwei
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