[SPDK] Re: The difference between vhost-nvme and vhost-blk

thanks, this helps a lot.


about the vfio-user,


I understand that in the vfio-user,
the guestOS can issue DMA read/write to a "pcie space " of a virtual device,
but I'm confused:
1. does the guestOS issue DMA read/write to region on actual physical device or just a DRAM region?
     if the guestOS directly access the physical device(DMA,IOMMU), where does spdk stands?
2. why do vfio-user need a socket, what kind of data does the socket carries?
3. Does the vfio-user look like the vhost-user except for direct DMA access instead of shared memory communication?


thanks














At 2022-03-08 17:40:12, "Thanos Makatos" <thanos.makatos(a)nutanix.com> wrote:
>> -----Original Message-----
>> From: zbhhbz <zbhhbz(a)yeah.net>
>> Sent: 08 March 2022 09:29
>> To: spdk <spdk(a)lists.01.org>
>> Subject: [SPDK] Re: The difference between vhost-nvme and vhost-blk
>> 
>> thanks, follow up questions:
>> 1. if I still use Vhost-user-blk-pci in qemu and with nvme ssd(bdev), i cant'
>> have access to the nvme feature in guest(shadow door bell). is that correct?
>
>Correct.
>
>> 2. in the vfio-user solution, does the interrupt sending from the ssd(nvme)
>> go through the qemu/kvm? or it go straight to the guest kernel?
>
>It doesn't go to QEMU/KVM. It depends on how you've set it up in SPDK: it can either go the host kernel or to SPDK.
>
>> 3. when will the vfio-user be available? does kvm have same delima here?
>
>vfio-user is under review in QEMU, so we can't predict when it will be accepted upstream. This doesn't mean you can't use it though, have a look here: https://github.com/nutanix/libvfio-user/blob/master/docs/spdk.md
>
>> 
>> 
>> thank you very much!
>> 
>> 
>> 
>> 
>> ---- 回复的原邮件 ----
>> | 发件人 | Liu, Changpeng<changpeng.liu(a)intel.com> |
>> | 日期 | 2022年03月08日 16:33 |
>> | 收件人 | Storage Performance Development Kit<spdk(a)lists.01.org> |
>> | 抄送至 | |
>> | 主题 | [SPDK] Re: The difference between vhost-nvme and vhost-blk |
>> Previously SPDK extended QEMU with a separate driver to enable vhost-
>> nvme, this driver
>> was not accepted by QEMU, so now we support emulated NVMe with a new
>> solution
>> "vfio-user", again the driver for supporting this is still under code review of
>> QEMU community,
>> but SPDK already supports this.
>> 
>> > -----Original Message-----
>> > From: zbhhbz(a)yeah.net <zbhhbz(a)yeah.net>
>> > Sent: Tuesday, March 8, 2022 4:29 PM
>> > To: spdk(a)lists.01.org
>> > Subject: [SPDK] The difference between vhost-nvme and vhost-blk
>> >
>> > Could someone help me understand the difference between vhost-nvme
>> and
>> > vhost-blk?
>> > The online doc only shows there is vhost-user-blk-pci, why not vhost-user-
>> nvme-
>> > pci?
>> > There is little doc fined in github/spdk and the qemu itself doesn't help
>> either
>> > Thanks!
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