On Wed, Jan 22, 2014, Sagi Grimberg <sagig@xxxxxxxxxxxxxxxxxx> wrote: > On 1/22/2014 2:43 AM, Roland Dreier wrote: >> On Tue, Jan 21, 2014, Or Gerlitz <or.gerlitz@xxxxxxxxx> wrote: >>> Roland, ping! the signature patches were posted > three months ago. We >>> deserve a response from the maintainer that goes beyond "I need to >>> think on that". Responsiveness was stated by Linus to be the #1 requirement >>> from kernel maintainers. > Hi Roland, I'll try to respond here. removing LKML and adding Linux-scsi. Sorry, it seems we will not getting responses unless coping LKML, so lets do that again -- Roland, below is the detailed response Sagi wrote you following your "adds a bunch of complexity to support a feature no one really cares about" comment, can we get you to respond on that? >> Or, I'm not sure what response you're after from me. Linus has also >> said that maintainers should say "no" a lot more >> (http://lwn.net/Articles/571995/) so maybe you want me to say, "No, I >> won't merge this patch set, since it adds a bunch of complexity to >> support a feature no one really cares about." > 1. I disagree about no-one cares about DIF/DIX. We are witnessing growing > interests in this especially for RDMA. > 2. We put a lot of efforts to avoid complexity here and plug-in as simple as > possible. > Application that will choose to use DIF will implement only 3 steps: > a. allocate signature enabled MR. > b. register signature enabled MR with DIF attributes (via post_send) and > then do RDMA. > c. check MR status after transaction is completed (_lightweight_ verb that > can be called from interrupt context). >> Is that it? (And yes I am skeptical about this stuff -- I work at an enterprise >> storage company and even here it's hard to find anyone who cares about >> DIF/DIX, especially offload features that stop it from being end-to-end) > 1. RDMA verbs are _NOT_ stopping DIF from being end-to-end. > OS (or SCSI in our specific case) passes LLD 2 scatterlists: data {block1, > block2, block3,...}, and protection {DIF1, DIF2, DIF3}. > LLD is required to verify the data integrity (block guards) and to > interleave over the wire {block1, DIF1, block2, DIF2....}. > You must support that in HW, you rather iSER/SRP will use giant copy's to > interleave by itself? or in case OS asked LLD > to INSERT DIF iSER/SRP will compute CRC for each data-block? RDMA storage > ULPs are transports - they should have no business with > data processing. > 2. HW DIF offload also gives you protection across the PCI. the > data-validation is done (hopefully offloaded) also > when data+protection are written to the back-end device. end-to-end is > preserved. > 3. SAS & FC have T10-PI offload. This is just adding RDMA into the game. > With this set of verbs iSER, SRP, FCoE Initiators and targets will be able > to support T10-PI. >> I'm sure you're not expecting me to say, "Sure, I'll merge it without >> understanding the problem it's solving > Problem: T10-PI offload support for RDMA based initiators. Supporting > end-to-end data integrity while sustaining high RDMA performance. >> or how it's doing that," > How it's doing that: > - We introduce a new type of memory region that posses protection attributes > suited for data integrity offload. > - We Introduce a new fast registration method that can bind all the relevant > info for verify/generate of protection information: > * describe if/how to interleave data with protection. > * describe what method of data integrity is used (DIF type X, CRC, XOR...) > and the seeds that HW should start calculation from. > * describe how to verify the data. > - We Introduce a new lightweight check of the data-integrity status to check > if there were any integrity errors and get information on them. > Note: We made MR allocation routine generic enough to lay a framework to > unite all MR allocation > methods (get_dma_mr, alloc_fast_reg_mr, reg_phys, reg_user_mr, fmrs, and > probably more in the future...). > We defined ib_create_mr that can actually get mr_init_attr which can be > easily extended as opposed to the specific calls exists today. > So I would say this even reduces complexity. > Hope this helps, > Sagi. -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
