[SPDK] SPDK performance questions

Abhik Sarkar Abhik.Sarkar at riverbed.com
Tue Jun 6 10:40:36 PDT 2017


I have a couple of questions regarding the data I have gathered so far on SCSI based disks with SPDK using libaio on host.


1.       Our FIO results on host, a 2 socket, 16 core box is around 2.05 GBps. I have been able to push it to 1.88 GBps with SPDK-vhost running on a single core handling 7 request queues (1 queue per disk) or in other words from vhost point of view

it sees 7 different unix sockets and from guest point of view one disk per scsi host. But when I have a single scsi host with 7 target devices, the performance goes down to 1.38 GBps. Is this performance boost coming from guest being able to populate separate queues in parallel, as there is only a single vhost thread handling the requests. Is my understanding correct? Will we get the same performance by adding multiple virtio-scsi-pci devices and interfacing each disk with a different virtio device?

2.       Another observation is that, if I try to distribute it between 2 cores, the throughput drops down to bw=1408MiB/s (1476MB/s). Here, I see that the vhost app has an additional thread. With additional thread handling disjoint set of queues,

I would have imagined that there should be some performance boost. But here it seemed to have dropped. Is there a lock contention of some sort? On the host, all these devices are on a single SCSI host.

3.       Since, we are not using a userspace driver, rather relying on libaio, will it be more efficient to use kernel-vhost?

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