Daniel Debonzi, on 03/20/2009 09:01 PM wrote: > Love, Robert W wrote: >> Daniel Debonzi wrote: >>> Hi all, >>> >>> I am starting to get in touch with the Open FCoE project (and also the >>> Fibre Channel thing itself) and as far as one of my tasks is work with >>> the Open FCoE target I started to gather information regarding that. >>> >>> I had an initial conversation with Robert but we didn't entered to >>> much in details about the target so as he mentioned a good place to >>> figure things out is here. >>> >>> >>> First of all, I apologize in advance if I write something really >>> stupid or non-sense because as I wrote before, I am just starting. >>> >>> The first thing I would like to ask about is the status of the FCoE >>> target and how dependent on the SCST project it is. >>> > > >> The status is that it's mostly rotting and may not be functional as-is. >> It's based on our old initiator code as well as SCST, neither of which >> are in-kernel. >> >> Sivaram, Joe and Mike have been discussing some patches recently to >> update the target to get it working again. >> >> IMO if we want an FCoE target we need to decide on which framework to >> use. Either SCST needs to get in-kernel or we need to base the FCoE >> target on stgt. My understanding is that the main difference in the >> two projects is that SCST is mostly kernel code where stgt is mostly >> user space code (with some kernel components which are allready upstream). >> There have been a lot of technical discussions on the subject of >> what the target infrastructure should look like on linux-scsi. >> >> So, depending on which direction is decided upon one would then need >> to either hook our upstream initiator into SCST (once it's upstream) >> or port our current initiator code to userspace to work with stgt. > > I know that there is already a FCoE target implementation using SCST but > as long as it probably needs a re-factory and also SCST didn't get into > kernel I fell that have it using tgt would be a good idea. Reasons: > > - Would allow a fully user space implementation (I am supposing that > the actual implementation have some kernel bits). > > - The kernel parts of tgt are already on the mainline kernel which I > believe would make any FCoE contribution to tgt get to the mainline > kernel easier. > > I am not considering performance on that because I don't have this info.
Target drivers for SCST has better performance than target drivers for STGT not only because they are in the kernel, but also because in-kernel architecture of SCST allows things, not possible from user space STGT. Particularly: - Zero-copy FILEIO. This feature is fundamentally impossible from user space. I don't think you will doubt that zero-copy data access is a big performance win. - Zero-copy network send. - Fully asynchronous BLOCKIO. - Access to IO threads IO context. - Much simpler and more effective asynchronous FILEIO. - etc. _______________________________________________ devel mailing list [email protected] http://www.open-fcoe.org/mailman/listinfo/devel
