Il 18/12/2012 23:18, Rolf Eike Beer ha scritto: > Paolo Bonzini wrote: >> Hi all, >> >> this series adds multiqueue support to the virtio-scsi driver, based >> on Jason Wang's work on virtio-net. It uses a simple queue steering >> algorithm that expects one queue per CPU. LUNs in the same target always >> use the same queue (so that commands are not reordered); queue switching >> occurs when the request being queued is the only one for the target. >> Also based on Jason's patches, the virtqueue affinity is set so that >> each CPU is associated to one virtqueue. >> >> I tested the patches with fio, using up to 32 virtio-scsi disks backed >> by tmpfs on the host. These numbers are with 1 LUN per target. >> >> FIO configuration >> ----------------- >> [global] >> rw=read >> bsrange=4k-64k >> ioengine=libaio >> direct=1 >> iodepth=4 >> loops=20 >> >> overall bandwidth (MB/s) >> ------------------------ >> >> # of targets single-queue multi-queue, 4 VCPUs multi-queue, 8 VCPUs >> 1 540 626 599 >> 2 795 965 925 >> 4 997 1376 1500 >> 8 1136 2130 2060 >> 16 1440 2269 2474 >> 24 1408 2179 2436 >> 32 1515 1978 2319 >> >> (These numbers for single-queue are with 4 VCPUs, but the impact of adding >> more VCPUs is very limited). >> >> avg bandwidth per LUN (MB/s) >> ---------------------------- >> >> # of targets single-queue multi-queue, 4 VCPUs multi-queue, 8 VCPUs >> 1 540 626 599 >> 2 397 482 462 >> 4 249 344 375 >> 8 142 266 257 >> 16 90 141 154 >> 24 58 90 101 >> 32 47 61 72 > > Is there an explanation why 8x8 is slower then 4x8 in both cases?
Regarding the "in both cases" part, it's because the second table has the same data as the first, but divided by the first column. In general, the "strangenesses" you find are probably within statistical noise or due to other effects such as host CPU utilization or contention on the big QEMU lock. Paolo 8x1 and 8x2 > being slower than 4x1 and 4x2 is more or less expected, but 8x8 loses against > 4x8 while 8x4 wins against 4x4 and 8x16 against 4x16. > > Eike > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
