Re: [PATCH 00/12] virtio-scsi: add iothread-vq-mapping parameter

[Kevin Wolf <kwolf@redhat.com>]

Am 13.02.2025 um 19:00 hat Stefan Hajnoczi geschrieben:
> Implement --device virtio-scsi-pci,iothread-vq-mapping= support so that
> virtqueues can be assigned to different IOThreads. This improves SMP guest
> scalability where I/O-intensive applications can become bottlenecked on a
> single IOThread.
> 
> The following benchmark results show the effect of iothread-vq-mapping. fio
> randread 4k iodepth=64 results from a 4 vCPU guest with an Intel P4800X SSD:
> iothreads IOPS
> ------------------------------
> 1         189576
> 2         312698
> 4         346744
> 
> The virtio-scsi device model and core SCSI emulation currently assume that
> requests are processed in a single AioContext. This patch series goes about
> modifying this as follows:
> 
> scsi-disk: drop unused SCSIDiskState->bh field
> dma: use current AioContext for dma_blk_io()
> 
> Make dma-helpers.c support the QEMU multi-queue block layer by using
> qemu_get_current_aio_context().
> 
> scsi: track per-SCSIRequest AioContext
> scsi: introduce requests_lock
> 
> Make the core SCSI emulation code support processing requests in multiple
> AioContexts by protecting the per-SCSIDevice requests list.
> 
> virtio-scsi: introduce event and ctrl virtqueue locks
> virtio-scsi: protect events_dropped field
> virtio-scsi: perform TMFs in appropriate AioContexts
> 
> Make the virtio-scsi emulation code support processing requests in multiple
> AioContexts. The event and ctrl virtqueues can interact with multiple
> AioContexts. Especially the SCSI Task Management Functions (TMFs) handled by
> the ctrl virtqueue need to be made thread-safe.
> 
> virtio-blk: extract cleanup_iothread_vq_mapping() function
> virtio-blk: tidy up iothread_vq_mapping functions
> virtio: extract iothread-vq-mapping.h API
> virtio-scsi: add iothread-vq-mapping parameter
> 
> Port over the iothread-vq-mapping qdev property from virtio-blk to virtio-scsi.
> 
> virtio-scsi: handle ctrl virtqueue in main loop
> 
> Simplify TMF handling now that there is no longer a single AioContext where all
> requests are processed.
> 
> Stefan Hajnoczi (12):
>   scsi-disk: drop unused SCSIDiskState->bh field
>   dma: use current AioContext for dma_blk_io()
>   scsi: track per-SCSIRequest AioContext
>   scsi: introduce requests_lock
>   virtio-scsi: introduce event and ctrl virtqueue locks
>   virtio-scsi: protect events_dropped field
>   virtio-scsi: perform TMFs in appropriate AioContexts
>   virtio-blk: extract cleanup_iothread_vq_mapping() function
>   virtio-blk: tidy up iothread_vq_mapping functions
>   virtio: extract iothread-vq-mapping.h API
>   virtio-scsi: add iothread-vq-mapping parameter
>   virtio-scsi: handle ctrl virtqueue in main loop

Patches 1-10: Reviewed-by: Kevin Wolf <kwolf@redhat.com>