Hi Stefan, I am working on something to move PCI devices to data plane architecture. Do you know any know reasons, as to why this was not tried before ?
Regards, On Fri, Jun 24, 2016 at 3:45 PM, Stefan Hajnoczi <stefa...@gmail.com> wrote: > On Thu, Jun 23, 2016 at 08:56:34PM +0530, Gaurav Sharma wrote: > > Hi, > > I am trying to explore how the data plane mechanism works in QEMU. I > > understand the behavior of QEMU big lock. Can someone clarify the > following > > w.r.t. to data plane : > > > > 1. Currently only virtio-blk-pci and virtio-scsi-pci have data plane > > enabled ? > > Yes. > > > 2. From qemu 2.1.0 data plane is enabled by default. > > No "enabled by default" would mean that existing QEMU command-lines > enable dataplane. This is not the case. You have to explicitly define > an iothread object and then associate a virtio-blk/virtio-scsi device > with it. > > > I specify the > > following options in the command line to enable : > > -enable-kvm -drive if=none,id=drive1,file=file_name -object > > iothread,id=iothread2 -device > > virtio-blk-pci,id=drv0,drive=drive1,iothread=iothread2 > > Is the above syntax correct ? > > Yes. > > > 3. What is the best possible scenario to test data plane ? Currently, I > > have a test set up wherein i have two different devices [dev1 and dev2]. > If > > i process a write to dev1 which i made blocking by putting a sleep > > statement, will i be able to process write on dev2 ? My understanding is > > that as in case of dataplane we have a different event loop, i should be > > able to process write on dev2. Is this correct ? > > Dataplane improves scalability for high IOPS workloads when there are > multiple disks. > > You do not need to modify any code in order to benchmark dataplane. Run > fio inside an SMP 4 guest with 4 disks (you can use the host Linux > kernel's null_blk driver) and you should find that QEMU without > dataplane has lower iops. The difference should become clear around 4 > or 8 vcpus/disks. > > Stefan >
