| Message ID | 1553682995-5682-1-git-send-email-dongli.zhang@oracle.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | Limit number of hw queues by nr_cpu_ids for virtio-blk and virtio-scsi | expand |
ping? Thank you very much! Dongli Zhang On 03/27/2019 06:36 PM, Dongli Zhang wrote: > When tag_set->nr_maps is 1, the block layer limits the number of hw queues > by nr_cpu_ids. No matter how many hw queues are use by > virtio-blk/virtio-scsi, as they both have (tag_set->nr_maps == 1), they > can use at most nr_cpu_ids hw queues. > > In addition, specifically for pci scenario, when the 'num-queues' specified > by qemu is more than maxcpus, virtio-blk/virtio-scsi would not be able to > allocate more than maxcpus vectors in order to have a vector for each > queue. As a result, they fall back into MSI-X with one vector for config > and one shared for queues. > > Considering above reasons, this patch set limits the number of hw queues > used by nr_cpu_ids for both virtio-blk and virtio-scsi. > > ------------------------------------------------------------- > > Here is test result of virtio-scsi: > > qemu cmdline: > > -smp 2,maxcpus=4, \ > -device virtio-scsi-pci,id=scsi0,num_queues=8, \ > -device scsi-hd,drive=drive0,bus=scsi0.0,channel=0,scsi-id=0,lun=0, \ > -drive file=test.img,if=none,id=drive0 > > Although maxcpus=4 and num_queues=8, 4 queues are used while 2 interrupts > are allocated. > > # cat /proc/interrupts > ... ... > 24: 0 0 PCI-MSI 65536-edge virtio0-config > 25: 0 369 PCI-MSI 65537-edge virtio0-virtqueues > ... ... > > # /sys/block/sda/mq/ > 0 1 2 3 ------> 4 queues although qemu sets num_queues=8 > > > With the patch set, there is per-queue interrupt. > > # cat /proc/interrupts > 24: 0 0 PCI-MSI 65536-edge virtio0-config > 25: 0 0 PCI-MSI 65537-edge virtio0-control > 26: 0 0 PCI-MSI 65538-edge virtio0-event > 27: 296 0 PCI-MSI 65539-edge virtio0-request > 28: 0 139 PCI-MSI 65540-edge virtio0-request > 29: 0 0 PCI-MSI 65541-edge virtio0-request > 30: 0 0 PCI-MSI 65542-edge virtio0-request > > # ls /sys/block/sda/mq > 0 1 2 3 > > ------------------------------------------------------------- > > Here is test result of virtio-blk: > > qemu cmdline: > > -smp 2,maxcpus=4, > -device virtio-blk-pci,drive=drive-virtio-disk0,id=virtio-disk0,num-queues=8 > -drive test.img,format=raw,if=none,id=drive-virtio-disk0 > > Although maxcpus=4 and num-queues=8, 4 queues are used while 2 interrupts > are allocated. > > # cat /proc/interrupts > ... ... > 24: 0 0 PCI-MSI 65536-edge virtio0-config > 25: 0 65 PCI-MSI 65537-edge virtio0-virtqueues > ... ... > > # ls /sys/block/vda/mq > 0 1 2 3 -------> 4 queues although qemu sets num_queues=8 > > > With the patch set, there is per-queue interrupt. > > # cat /proc/interrupts > 24: 0 0 PCI-MSI 65536-edge virtio0-config > 25: 64 0 PCI-MSI 65537-edge virtio0-req.0 > 26: 0 10290 PCI-MSI 65538-edge virtio0-req.1 > 27: 0 0 PCI-MSI 65539-edge virtio0-req.2 > 28: 0 0 PCI-MSI 65540-edge virtio0-req.3 > > # ls /sys/block/vda/mq/ > 0 1 2 3 > > > Reference: https://lore.kernel.org/lkml/e4afe4c5-0262-4500-aeec-60f30734b4fc@default/ > > Thank you very much! > > Dongli Zhang >
On 3/27/19 4:36 AM, Dongli Zhang wrote: > When tag_set->nr_maps is 1, the block layer limits the number of hw queues > by nr_cpu_ids. No matter how many hw queues are use by > virtio-blk/virtio-scsi, as they both have (tag_set->nr_maps == 1), they > can use at most nr_cpu_ids hw queues. > > In addition, specifically for pci scenario, when the 'num-queues' specified > by qemu is more than maxcpus, virtio-blk/virtio-scsi would not be able to > allocate more than maxcpus vectors in order to have a vector for each > queue. As a result, they fall back into MSI-X with one vector for config > and one shared for queues. > > Considering above reasons, this patch set limits the number of hw queues > used by nr_cpu_ids for both virtio-blk and virtio-scsi. I picked both up for 5.1.