[ofa-general] RDMA write completion question

[Caitlin Bestler]

Steve Wise Wrote:

-----Original Message-----

Devesh Sharma wrote:
> On 5/24/07, Gleb Natapov <glebn at voltaire.com> wrote:
>> Hi,
>>
>>  Does local RDMA write completion guaranties that a data that was 
>> RDMAed is
>> already accessible in a destination's host _memory_?
> Local RDMA write completion guarantees that the data you have RDMAed
> has been copied into the remote buffer, without any data corruption.
>>
For iWARP, the local write completion simply means you can reuse the 
local buffer and the the transport will deliver it or kill the 
connection.  The data _could_ be queued in the local rnic and anywhere 
else in the tcp cloud.


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And The only real difference with InfiniBand is that the uncertainty
cloud is limited to the gap between the HCA and the application.
Protocol designers can debate the tradeoffs InfiniBand takes to
achieve that, but the import thing to Application Designers is
that "smaller" is not "zero".

Generally, once a Send has been posted that all other interactions
with the remote peer over the same connection can assume that the prior
actions have completed, but if your application needs an absolute
guarantee that something has happened (for checkpointing or other
purposes) then you really can only rely on a peer-to-peer message.