Thanks for the help along my understanding with IB and uDAPL.
Is that possible to spin remote memory of a rdma atomic compare and swap
(dat_ib_post_cmp_and_swap())?
I have wrote a program that initiator atomic cmp_swap a value to a
remote memory.
Instead of sending a message to notify the remoter about the completion
of cmp_swap,
the remoter actually doing a memory spin to test the update on the
memory (e.g. while(target == 0);).
However, at remote side, this while loops goes infinitely, and the
initiator has already received DAT_IB_DTO_EVENT.
I don't really understand what's going on, and what would be a correct
way to spin memory for checking remote
write updates.
Any suggestions?
Regards,
Jie
--
Jie Cai
Caitlin Bestler wrote:
On Tue, Mar 31, 2009 at 11:41 PM, Jie Cai <[email protected]> wrote:
Understood now. A further question is here again.
To implement software level acknowledgment to inform initiator that data
has been available for remoter, is that possible to use a busy loop at
remote
side to detect the last element of transferring has appear in the memory.
Or remoter has to wait for the event of recv matching initiator's send, then
send a message back to initiator as a acknowledgment?
There are two issues when spinning on a remote memory update.
The first is that packets may be received and processed out of order,
especially for iWARP. Therefore the fact that the last byte has been
received and placed does not guarantee that the prior packets have
been received and placed.
More importantly, the order in which updates become visible to a
specific software thread can make the order of updates unpredictable
to the application.
When delivering a completion the Provider is responsible for dealing
with both of these problems. So when you reap a completion from the
CQ, the operation it represents (and all prior operations) are complete.
There are no gaps in received packets, nothing is still sitting on an
Adapter buffer waiting to be placed in host memory.
If your application does not want to block you can consider polling
the cq whether than enabling notifications. But polling memory locations
directly should only be done when you're willing to have bus/adapter
specific dependencies. You working code might stop working when
your network changes, or you install a new Adapter that has a different
strategy for optimizing its writes over the PCIe bus.
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