On Wed, Dec 19, 2012 at 09:52:59AM +0100, Paolo Bonzini wrote: > 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 > That's exactly what bothers me. If the IOPS divided by host CPU goes down, then the win on lightly loaded host will become a regression on a loaded host. Need to measure that. > 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 linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
