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List:       linux-kernel
Subject:    Re: [PATCH] I/O space write barrier
From:       Jesse Barnes <jbarnes () sgi ! com>
Date:       2004-10-22 3:05:50
Message-ID: 200410212205.51672.jbarnes () sgi ! com
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On Thursday, October 21, 2004 8:01 pm, Grant Grundler wrote:
> > +<programlisting>
> > +       sp->flags |= SRB_SENT;
> > +       ha->actthreads++;
> > +       WRT_REG_WORD(&amp;reg->mailbox4, ha->req_ring_index);
> > +
> > +       /*
> > +        * A Memory Mapped I/O Write Barrier is needed to ensure that
> > this write +        * of the request queue in register is ordered ahead
> > of writes issued +        * after this one by other CPUs.  Access to the
> > register is protected +        * by the host_lock.  Without the mmiowb,
> > however, it is possible for +        * this CPU to release the host lock,
> > another CPU acquire the host lock, +        * and write to the request
> > queue in, and have the second write make it +        * to the chip first.
> > +        */
> > +       mmiowb(); /* posted write ordering */
> > +</programlisting>
>
> This is the example code I'd like to see replaced with your
> synthetic example above.

Ok, that makes sense.  I'd like to update the documentation with a separate 
patch though, if that's ok with you.  I think Greg had some ideas about other 
things to cover as well.  Greg?

Thanks,
Jesse
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