[ofa-general] synchronize commands issued to MTHCA

[Yicheng Jia]

Hi Roland,

Could you tell me what's the difference between "wmb()" and "mmiowb()". I 
notice that ofa-1.3 has added "mmiowb()" at the end of mthca_cmd_post, 
since "wmb()" is already called at the end of cmd_post, is "mmiowb()" 
really necessary?

Thanks!
Yicheng




Roland Dreier <rdreier at cisco.com> 
01/02/2008 12:13 PM

To
Jack Morgenstein <jackm at dev.mellanox.co.il>
cc
general at lists.openfabrics.org, Yicheng Jia <YJia at tmriusa.com>
Subject
Re: [ofa-general] synchronize commands issued to MTHCA






 > Roland, do you think that the memcpy_toio() call might mess things up?

I wouldn't think so, although I don't have full details of how your
hardware behaves to know for sure.  I assume your PCI bus/memory
controller is already smart enough to deal with HCR writes being
interleaved with writes to a doorbell page from userspace, so it seems
that writes to locally attached memory should be OK too, as long as
the HCR writes are word-sized in the right order etc.

 > Maybe we need "wmb()" or "mmiowb()" here as well?

I don't see any reason, although I often miss things.  It seems that
the only thing that cares about the writes of the address info being
done would be posting a send WQE that uses it, and that should already
have sufficient ordering.  What would we be ordering things against?

 - R.

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