Michael suggested to me a while ago to try MSI with virtio-blk and I
played with this small patch:
Index: qemu-kvm/hw/virtio-blk.c
===================================================================
--- qemu-kvm.orig/hw/virtio-blk.c
+++ qemu-kvm/hw/virtio-blk.c
@@ -416,6 +416,7 @@ VirtIODevice *virtio_blk_init(DeviceStat
s->vdev.get_config = virtio_blk_update_config;
s->vdev.get_features = virtio_blk_get_features;
s->vdev.reset = virtio_blk_reset;
+ s->vdev.nvectors = 2;
s->bs = bs;
s->rq = NULL;
if (strlen(ps = (char *)drive_get_serial(bs)))
which gave about 5% speedups on 4k sized reads and writes, see the full
iozone output I attached. Now getting the information about using
multiple MSI vectors from the command line to virtio-blk similar to how
virtio-net does seems extremly messy right now. Waiting for Gerd's
additional qdev patches to make it easier as a qdev property.
File size set to 131072 KB
Record Size 4 KB
O_DIRECT feature enabled
Command line used: iozone -s 128m -r 4k -I -f /dev/sdb
Output is in Kbytes/sec
Time Resolution = 0.000001 seconds.
Processor cache size set to 1024 Kbytes.
Processor cache line size set to 32 bytes.
File stride size set to 17 * record size.
random random bkwd record stride
KB reclen write rewrite read reread read write read rewrite read fwrite frewrite fread freread
native 131072 4 11428 11847 25110 25302 24415 10904 25051 12146 24859 978572 1224433 1974096 2086567
131072 4 11812 11784 24941 25209 24325 10776 24814 12271 24907 959819 1208770 1977191 2103138
131072 4 11834 11892 25270 25347 24427 10839 24571 12161 24558 958934 1213707 1959754 2100647
131072 4 11688 11914 25102 25100 24514 10855 24787 12237 24738 987739 1218774 1985245 2085435
131072 4 11768 11910 24986 25087 24342 10819 24687 12304 24711 974889 1221511 2027124 2102430
qemu 131072 4 8752 9137 14020 14181 13924 8491 14158 8215 13816 378448 1498838 2117166 2341281
131072 4 9113 9097 14019 14187 14024 8536 14153 8243 14132 1194485 1506540 2053520 2333202
131072 4 9082 9128 14001 14232 13971 8541 14113 8216 14103 1260659 1464543 2101490 2335442
131072 4 9103 9163 14373 14149 13983 8523 14171 8242 14026 1278104 1503047 2127449 2334738
131072 4 9084 9128 14103 14212 13980 8519 14064 8260 13810 1204696 1497434 2053129 2334362
qemu+msi 131072 4 9466 9726 15339 15225 14845 8884 15159 8631 14460 375140 1488522 2066115 2337399
131072 4 9541 9590 15025 15059 15010 8852 15007 8677 14736 1142718 1491640 2111847 2332153
131072 4 9492 9621 14831 15093 14792 8895 14849 8452 14976 1163760 1461825 2118741 2337985
131072 4 9519 9615 14954 14950 14713 8915 15229 8547 14854 1212529 1490471 2091894 2343676
131072 4 9527 9576 14872 14828 14741 8880 14891 8769 14502 1253559 1436703 2127827 2344256
