> -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Joerg Zinke > Sent: Tuesday, October 25, 2005 2:40 AM > To: [email protected] > Subject: [openib-general] question about poll_cq() > > hi, > > i hope it's ok to ask this question here. > i just want to know more about poll_cq(). > the standard seems to define only the input/ouput-params. > after reading the code i figured out that there is some kind > of "mapping" from libibverbs to the device specific "plugin" (mthca). > so it looks like that the ibv_poll_cq() call from the userspace (e.g. > ibv_xx_pingpong) finally ends in a call of: mthca_poll_cq() > in mthca_cq.c > > so my question is: can someone give me a brief summary what > mthca_poll_cq (or mthca_poll_one()) is really doing? > i want to know how polling the completion queue really works, > there must be some kind of low-level acknowledge/response- > message if a new entry enters the cq? > where is the completion queue really located (on a rdma > operation) - local or remote? >
Understanding how a given device implements poll_cq is legitimate if the purpose is debugging and/or understanding memory/bus utilization. However it is one of those that you SHOULD NOT know when righting code that uses poll_cq. What will vary over time and model is where the work completions are stored (in device and/or host memory) how they are formatted and whether they are self contained or reference other data (such as the original work request). The work completion that you get from a successful poll_cq may never have existed as that sequence of bytes until you made the call to poll_cq. If these things were not deliberately undefined then there would be no need for both ibv_poll_cq and device specific methods. For a discussion on what you can assume about a CQ across all devices I'd suggest reviewing the IBTA and/or RDMAC verbs. But basically, about all that is guaranteed is that it is a reliable ordered queued that the Consumer MUST provision adequately so as to avoid overflows. _______________________________________________ openib-general mailing list [email protected] http://openib.org/mailman/listinfo/openib-general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
