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
>>
