On Sun, 2017-03-26 at 08:31 -0600, Alex Williamson wrote: > On Sun, Mar 26, 2017 at 4:33 AM, Patrick O'Callaghan <[email protected]> wrote: > > > On Sun, 2017-03-26 at 10:58 +0100, Bronek Kozicki wrote: > > > Assuming you use libvirt, make sure to use vCPU pinning. For disk > > > > access, try cache='writeback' io='threads'. If you switch to scsio-vfio, > > this will give you the ability to define queue length which might > > additionally improve IO. Also, try QCOW2 format for guest disk, it might > > enable some additional optimizations. However given you host seem to have > > little spare capacity, YMMV > > > > Thanks. I'm already using CPU pinning as I said. The disk options are > > both set to "hypervisor default" so I'll try changing them. I'd > > configured the guest disk as 'raw' assuming that would be faster than > > QCOW2 but I'll look into it. > > > > Generally the recommendation is to use raw (not sparse), LVM, or a block > device for the best performance. QCOW is never going to be as fast as > these at writing unused blocks since it needs to go out and allocate new > blocks from the underlying file system when this happens. QCOW is > generally recommended when on disk image size is a concern or you want > advanced features like backing images, snapshots, etc. I think real world > performance of QCOW is noticeably worse than the recommended image types. > Also, be careful with caching, it's easy to get into a situation where the > benchmark shows it to be great, sometime unbelievably so, but perhaps at > the cost of safe operation or to the determent of overall system behavior. > For example, do you really want to sacrifice buffer cache in the host for > the benefit of the guest. Thanks,
Understood. I converted from raw to qcow2 and it was no worse for speed in my use case (in fact it felt subjectively a little faster), and the ability to do snapshots does interest me. No-one has commented on the keyboard overrun issue I asked about. That's really more noticeable at this stage than file I/O. I moved the wireless hub to a USB-3 port and again it may have made a slight difference, but some stuttering still occurs, i.e. holding down a key will quite quickly (say 5 seconds ballpark) fill the input buffer and generate an audio buzz. poc _______________________________________________ vfio-users mailing list [email protected] https://www.redhat.com/mailman/listinfo/vfio-users
