I got the same result when emulating nvme with qemu: the VM has 12 cpu, while the num_queues of nvme is 8. # uname -r 4.14.1 # ll /sys/block/nvme*n1/mq/*/cpu_list -r--r--r-- 1 root root 4096 Oct 8 14:30 /sys/block/nvme0n1/mq/0/cpu_list -r--r--r-- 1 root root 4096 Oct 8 14:30 /sys/block/nvme0n1/mq/1/cpu_list -r--r--r-- 1 root root 4096 Oct 8 14:30 /sys/block/nvme0n1/mq/2/cpu_list -r--r--r-- 1 root root 4096 Oct 8 14:30 /sys/block/nvme0n1/mq/3/cpu_list -r--r--r-- 1 root root 4096 Oct 8 14:30 /sys/block/nvme0n1/mq/4/cpu_list -r--r--r-- 1 root root 4096 Oct 8 14:30 /sys/block/nvme0n1/mq/5/cpu_list -r--r--r-- 1 root root 4096 Oct 8 14:30 /sys/block/nvme0n1/mq/6/cpu_list # uname -r 4.18.10 # ll /sys/block/nvme*n1/mq/*/cpu_list -r--r--r-- 1 root root 4096 Oct 8 14:34 /sys/block/nvme0n1/mq/0/cpu_list -r--r--r-- 1 root root 4096 Oct 8 14:34 /sys/block/nvme0n1/mq/1/cpu_list -r--r--r-- 1 root root 4096 Oct 8 14:34 /sys/block/nvme0n1/mq/2/cpu_list -r--r--r-- 1 root root 4096 Oct 8 14:34 /sys/block/nvme0n1/mq/3/cpu_list -r--r--r-- 1 root root 4096 Oct 8 14:34 /sys/block/nvme0n1/mq/4/cpu_list -r--r--r-- 1 root root 4096 Oct 8 14:34 /sys/block/nvme0n1/mq/5/cpu_list -r--r--r-- 1 root root 4096 Oct 8 14:34 /sys/block/nvme0n1/mq/6/cpu_list >From below qemu source code, when n->num_queues is 8, the handler of NVME_FEAT_NUM_QUEUES returns 0x60006. 719 static uint16_t nvme_set_feature(NvmeCtrl *n, NvmeCmd *cmd, NvmeRequest *req) 720 { 721 uint32_t dw10 = le32_to_cpu(cmd->cdw10); 722 uint32_t dw11 = le32_to_cpu(cmd->cdw11); 723 724 switch (dw10) { 725 case NVME_VOLATILE_WRITE_CACHE: 726 blk_set_enable_write_cache(n->conf.blk, dw11 & 1); 727 break; 728 case NVME_NUMBER_OF_QUEUES: 729 trace_nvme_setfeat_numq((dw11 & 0xFFFF) + 1, 730 ((dw11 >> 16) & 0xFFFF) + 1, 731 n->num_queues - 1, n->num_queues - 1); 732 req->cqe.result = 733 cpu_to_le32((n->num_queues - 2) | ((n->num_queues - 2) << 16)); ----> returns 0x60006 when num_queues is 8. Finally, nr_io_queues is set to 6+1=7 in nvme_set_queue_count() in VM kernel. I do not know how to paraphrase this in the world of nvme. Dongli Zhang On 10/08/2018 01:59 PM, Dongli Zhang wrote: > I can reproduce with qemu: > > # ls /sys/block/nvme*n1/mq/*/cpu_list > /sys/block/nvme0n1/mq/0/cpu_list > /sys/block/nvme0n1/mq/1/cpu_list > /sys/block/nvme0n1/mq/2/cpu_list > /sys/block/nvme0n1/mq/3/cpu_list > /sys/block/nvme0n1/mq/4/cpu_list > /sys/block/nvme0n1/mq/5/cpu_list > /sys/block/nvme0n1/mq/6/cpu_list > > Here is the qemu cmdline emulating 8-queue nvme while the VM has 12 cpu: > > # qemu-system-x86_64 -m 4096 -smp 12 \ > -kernel /path-to-kernel/linux-4.18.10/arch/x86_64/boot/bzImage \ > -hda /path-to-img/ubuntu1804.qcow2 \ > -append "root=/dev/sda1 init=/sbin/init text" -enable-kvm \ > -net nic -net user,hostfwd=tcp::5022-:22 \ > -device nvme,drive=nvme1,serial=deadbeaf1,num_queues=8 \ > -drive file=/path-to-img/nvme.disk,if=none,id=nvme1 > > Dongli Zhang > > > On 10/08/2018 01:05 PM, Prasun Ratn wrote: >> Hi >> >> I have an NVMe SSD that has 8 hw queues and on older kernels I see all >> 8 show up. However on a recent kernel (I tried 4.18), I only see 7. Is >> this a known issue? >> >> $ uname -r >> 4.14.1-1.el7.elrepo.x86_64 >> >> $ ls /sys/block/nvme*n1/mq/*/cpu_list >> /sys/block/nvme0n1/mq/0/cpu_list >> /sys/block/nvme0n1/mq/1/cpu_list >> /sys/block/nvme0n1/mq/2/cpu_list >> /sys/block/nvme0n1/mq/3/cpu_list >> /sys/block/nvme0n1/mq/4/cpu_list >> /sys/block/nvme0n1/mq/5/cpu_list >> /sys/block/nvme0n1/mq/6/cpu_list >> /sys/block/nvme0n1/mq/7/cpu_list >> /sys/block/nvme1n1/mq/0/cpu_list >> /sys/block/nvme1n1/mq/1/cpu_list >> /sys/block/nvme1n1/mq/2/cpu_list >> /sys/block/nvme1n1/mq/3/cpu_list >> /sys/block/nvme1n1/mq/4/cpu_list >> /sys/block/nvme1n1/mq/5/cpu_list >> /sys/block/nvme1n1/mq/6/cpu_list >> /sys/block/nvme1n1/mq/7/cpu_list >> /sys/block/nvme2n1/mq/0/cpu_list >> /sys/block/nvme2n1/mq/1/cpu_list >> /sys/block/nvme2n1/mq/2/cpu_list >> /sys/block/nvme2n1/mq/3/cpu_list >> /sys/block/nvme2n1/mq/4/cpu_list >> /sys/block/nvme2n1/mq/5/cpu_list >> /sys/block/nvme2n1/mq/6/cpu_list >> /sys/block/nvme2n1/mq/7/cpu_list >> /sys/block/nvme3n1/mq/0/cpu_list >> /sys/block/nvme3n1/mq/1/cpu_list >> /sys/block/nvme3n1/mq/2/cpu_list >> /sys/block/nvme3n1/mq/3/cpu_list >> /sys/block/nvme3n1/mq/4/cpu_list >> /sys/block/nvme3n1/mq/5/cpu_list >> /sys/block/nvme3n1/mq/6/cpu_list >> /sys/block/nvme3n1/mq/7/cpu_list >> >> >> $ uname -r >> 4.18.10-1.el7.elrepo.x86_64 >> >> $ ls /sys/block/nvme*n1/mq/*/cpu_list >> /sys/block/nvme0n1/mq/0/cpu_list >> /sys/block/nvme0n1/mq/1/cpu_list >> /sys/block/nvme0n1/mq/2/cpu_list >> /sys/block/nvme0n1/mq/3/cpu_list >> /sys/block/nvme0n1/mq/4/cpu_list >> /sys/block/nvme0n1/mq/5/cpu_list >> /sys/block/nvme0n1/mq/6/cpu_list >> /sys/block/nvme1n1/mq/0/cpu_list >> /sys/block/nvme1n1/mq/1/cpu_list >> /sys/block/nvme1n1/mq/2/cpu_list >> /sys/block/nvme1n1/mq/3/cpu_list >> /sys/block/nvme1n1/mq/4/cpu_list >> /sys/block/nvme1n1/mq/5/cpu_list >> /sys/block/nvme1n1/mq/6/cpu_list >> /sys/block/nvme2n1/mq/0/cpu_list >> /sys/block/nvme2n1/mq/1/cpu_list >> /sys/block/nvme2n1/mq/2/cpu_list >> /sys/block/nvme2n1/mq/3/cpu_list >> /sys/block/nvme2n1/mq/4/cpu_list >> /sys/block/nvme2n1/mq/5/cpu_list >> /sys/block/nvme2n1/mq/6/cpu_list >> /sys/block/nvme3n1/mq/0/cpu_list >> /sys/block/nvme3n1/mq/1/cpu_list >> /sys/block/nvme3n1/mq/2/cpu_list >> /sys/block/nvme3n1/mq/3/cpu_list >> /sys/block/nvme3n1/mq/4/cpu_list >> /sys/block/nvme3n1/mq/5/cpu_list >> /sys/block/nvme3n1/mq/6/cpu_list >>