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Date: Wed, 2 May 2007 02:54:40 +0200 From: Segher Boessenkool <segher@...nel.crashing.org> To: Scott Wood <scottwood@...escale.com> Cc: netdev@...r.kernel.org, linuxppc-dev@...abs.org, jgarzik@...ox.com Subject: Re: [PATCH] gianfar: Add I/O barriers when touching buffer descriptor ownership. > The hardware must not see that is given ownership of a buffer until it > is > completely written, and when the driver receives ownership of a buffer, > it must ensure that any other reads to the buffer reflect its final > state. Thus, I/O barriers are added where required. > > Without this patch, I have observed GCC reordering the setting of > bdp->length and bdp->status in gfar_new_skb. The :::"memory" in the barriers you used prevent GCC from reordering accesses around the barriers. AFAICS you need stronger barriers though; {w,r,}mb(), to prevent _any_ reordering of those memory accesses, not just the compiler-generated ones. Segher - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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