Date: Mon, 23 Apr 2012 15:38:38 +0400 From: Slawa Olhovchenkov <slw@zxy.spb.ru> To: Fengwei yin <yfw.bsd@gmail.com> Cc: jack.ren@intel.com, freebsd-threads@freebsd.org Subject: Re: About the memory barrier in BSD libc Message-ID: <20120423113838.GT32749@zxy.spb.ru> In-Reply-To: <CAPHpMukLUeetSKpH2oiKJQ3ML_PFHEi6a0hK3_Ery=LX1YEd3g@mail.gmail.com> 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> <CAPHpMukLUeetSKpH2oiKJQ3ML_PFHEi6a0hK3_Ery=LX1YEd3g@mail.gmail.com>
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On Mon, Apr 23, 2012 at 07:26:54PM +0800, Fengwei yin wrote:
> 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> wrote:
> >> > 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() š š__asm __volatile("lock; addl $0,(%%esp)" : : : "memory")
> >> > #define wmb() š __asm __volatile("lock; addl $0,(%%esp)" : : : "memory")
> >> > #define rmb() š __asm __volatile("lock; addl $0,(%%esp)" : : : "memory")
> >> >
> >>
> >> 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?
What architecture with cache incoherency and FreeBSD support?
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