On Sat, 2010-08-21 at 22:42 +0400, Vladislav Bolkhovitin wrote: > Nicholas A. Bellinger, on 08/20/2010 02:29 AM wrote: > > "We will be extending the scsi_tgt_[lib,if].c mapped ring interface to > > allow TCM to access userspace backstores transparently with existing > > kernel level TCM fabric modules, and using the generic configfs fabric > > module infrastructure in target_core_fabric_configfs.c for the port and > > I_T nexus control plane just as you would with any TCM backstore > > subsystem today. > > > > Again, in open source you have to build upon what already exists and > > move forward. The original STGT kernel<-> userspace ring abstraction > > and logic in drivers/scsi/scsi_tgt_lib.c:scsi_tgt_queue_command() -> > > scsi_tgt_uspace_send_cmd() is already going to do the vast majority of > > what is required for handling fabric I/O processing and I_T Nexus and > > Port management in kernel space with a userspace backstore. It is > > really just a matter of allowing the STGT ring request to optionally be > > sent out to userspace as a standalone LUN instead of as a target port." > > You forgot to mention one small thing. You are going to (re)use current > STGT interface for user space backend, which in 5 years of being > mainline has not gained any noticeable interest, because it is > fundamentally slow. That's not exactly what the results of a speed comparison one of your people did said, now is it? The results were actually not much difference on line speeds up to GigE. Interface re-use (or at least ABI compatibility) is the whole point, it's what makes the solution a drop in replacement. > It needs a complete redesign to become fast. In > contrast, interface provided by scst_user has just 3% overhead comparing > with fully in-kernel backend and allows to build storage capable of > handling 1,500,000 IOPSes (Kaminario). For a replacement, first we get the current userspace code working as is, then you can propose modifications to make it go faster. James -- 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
