[openib-general] [PATCH] use mmiowb after doorbell ring

[Michael S. Tsirkin]

Quoting r. Roland Dreier <rdreier at cisco.com>:
> Subject: Re: [PATCH] use mmiowb after doorbell ring
> 
>     Michael> BTW, something like this will be needed for userspace too?
> 
> Ugh, I forgot about that.
> 
> I don't think an mmiowb() equivalent is available from userspace.

Isn't this just an asm() command?

> However, the problem only arises if userspace uses the same QP/CQ/SRQ
> from multiple nodes at the same time -- so maybe we can live with this.

BTW, I think we really should implement proper rmb/wmb in arch.h.
Last time I looked we only had compiler barriers here, and
this means, I think, that a read from e.g. CQE contents could bypass
the read of the CQE valid bit.

-- 
MST