On Mon, May 16, 2022 at 05:38:31PM +0000, Raphael Norwitz wrote: > Hey Stefan, > > We've been thinking about ways to accelerate other disk types such as > SATA and IDE rather than translating to SCSI and using QEMU's iSCSI > driver, with existing and more performant backends such as SPDK. We > think there are some options worth exploring: > > [1] Keep using the SCSI translation in QEMU but back vDisks with a > vhost-user-scsi or vhost-user-blk backend device.
If I understand correctly the idea is to have a QEMU Block Driver that connects to SPDK using vhost-user-scsi/blk? > [2] Implement SATA and IDE emulation with vfio-user (likely with an SPDK > client?). This is definitely the option with the lowest overhead. I'm not sure if implementing SATA and IDE emulation in SPDK is worth the effort for saving the last few cycles. > [3] We've also been looking at your libblkio library. From your > description in > https://lists.gnu.org/archive/html/qemu-devel/2021-04/msg06146.html it > sounds like it may definitely play a role here, and possibly provide the > nessesary abstractions to back I/O from these emulated disks to any > backends we may want? Kevin Wolf has contributed a vhost-user-blk driver for libblkio. This lets you achieve #1 using QEMU's libblkio Block Driver. The guest still sees IDE or SATA but instead of translating to iSCSI the I/O requests are sent over vhost-user-blk. I suggest joining the libblkio chat and we can discuss how to set this up (the QEMU libblkio BlockDriver is not yet in qemu.git): https://matrix.to/#/#libblkio:matrix.org > We are planning to start a review of these options internally to survey > tradeoffs, potential timelines and practicality for these approaches. We > were also considering putting a submission together for KVM forum > describing our findings. Would you see any value in that? I think it's always interesting to see performance results. I wonder if you have more cutting-edge optimizations or performance results you want to share at KVM Forum because IDE and SATA are more legacy/niche nowadays? Stefan
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