Re: [storm] iSER draft
Alexander Nezhinsky <nezhinsky@gmail.com> Thu, 30 June 2011 18:07 UTC
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Date: Thu, 30 Jun 2011 21:07:46 +0300
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From: Alexander Nezhinsky <nezhinsky@gmail.com>
To: Michael Ko <Michael@huaweisymantec.com>
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Subject: Re: [storm] iSER draft
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On Thu, Jun 30, 2011 at 12:26 AM, Michael Ko <Michael@huaweisymantec.com>wrote: > ** > Tom, > > As originally written, the iSER spec always assumes ZBVA (zero-based > virtual address). But when iSER is used in conjunction with transports > other than iWARP, there is a need to include the virtual address for the > tagged buffer. Such is the case for Infiniband. Accordingly, the Virtual > Address field has been added to the iSCSI Control Type PDUs (sec. 9.2). > Alex pointed out that the tagged buffer should now be identified by the > 4-tuple (STag, VA, TO, and length) instead. This should be updated > everywhere where the term "tagged buffer" is mentioned in the spec. For > example, in sec. 1.1 under Advertisement, the sentence "A typical method > would be for the iSER Layer to embed the Tagged Buffer's STag, TO, and > buffer length in a Send Message destined for the remote iSER Layer" should > be modified to "A typical method would be for the iSER Layer to embed the > Tagged Buffer's STag, VA, TO, and buffer length in a Send Message destined > for the remote iSER Layer." BTW, this sentence also answers your question > as to whether VA is passed on the wire. > > Agree, using VA was in the draft already, I only suggested to clarify its use (and modes of use) from the level of definitions and up, so that it won't "suddenly" appear in the header format description section. > The Virtual Address is literally the virtual address of the tagged buffer. > The tagged offset is the displacement relative to the beginning of the > buffer starting at the virtual address. > > We could rephrase the definition of Virtual Address in sec. 1.1 as follows: > > "Virtual Address (VA) - This is the virtual address of the Tagged Buffer on > a Node. When set to 0, it indicates that a virtual address is not needed to > locate the Tagged Buffer." > > > Read and write buffers are identified by the combination of STag and VA. > OK. I tried to make the same point in the following: > Both fields should be required for any transport. This requirement does not > preclude > using ZBVA where possible. When VA is not used (as in iWARP) it is set to > 0. > > Below is the actually used format: > > struct iser_hdr { > uint8_t flags; > uint8_t rsvd[3]; > uint32_t write_stag; /* write rkey in IB */ > uint64_t write_va; > uint32_t read_stag; /* read rkey in IB */ > uint64_t read_va; > } > > I would like to add that InfiniBand does have ZBVA mode. It supposedly provides less than optimal performance with IB. And it is not exported through the current rdma-cm API, which supports RDMA/Ethernet as well, and is the only option to use RDMA in user space linux apps, as of today. So you could look at the additional fields as a kind of "reserved" in case of standard ZBVA implementation, used to practically support certain APIs and get enhanced performance in some cases. Alex
- [storm] iSER draft Alexander Nezhinsky
- Re: [storm] iSER draft Tom Talpey
- Re: [storm] iSER draft Michael Ko
- Re: [storm] iSER draft Caitlin Bestler
- Re: [storm] iSER draft Michael Ko
- Re: [storm] iSER draft Alexander Nezhinsky
- Re: [storm] iSER draft Tom Talpey
- Re: [storm] iSER draft Caitlin Bestler
- Re: [storm] iSER draft Michael Ko
- Re: [storm] iSER draft Tom Talpey
- Re: [storm] iSER draft Michael Ko
- Re: [storm] iSER draft Mallikarjun Chadalapaka
- Re: [storm] iSER draft Michael Ko
- Re: [storm] iSER draft Tom Talpey
- Re: [storm] iSER draft Mallikarjun Chadalapaka