On 07/20/2012 06:26 PM, Richard Yao wrote: > On 07/20/2012 03:44 PM, Adrian Chadd wrote: >> On 19 July 2012 11:27, Richard Yao <r...@gentoo.org> wrote: >>> Dear Everyone, >>> >>> FreeBSD 9 has awful block IO performance in KVM. I have experienced it >>> and others have experienced it. Someone posted slides to slideshare with >>> benchmarks documenting it: >>> >>> http://www.slideshare.net/TakeshiHasegawa1/runningfreebsdonlinuxkvm >>> >>> Slides 13 and 20 are particular eye openers. Does anyone know what is wrong? >> >> For those watching at home - this is bad performance _with_ the virtio >> drivers themselves, not just with SCSI emulation. >> >> Slide 17 is very telling - the operation latency is quite high. >> >> Richard, are you able to easily test out things on FreeBSD-HEAD guest >> in a Linux KVM? If so, some of the storage/block/GEOM driver people >> may be able to step up and start offering some ideas. >> >> Thanks, >> >> >> >> Adrian > > Dear Adrian, > > I am in the process of setting up a VM instance specifically for this. > While installing it, I noticed that qemu-kvm printed 'lsi_scsi: error: > ORDERED queue not implemented', which might be a clue as to why the > block device performance is bad. > > Also, I will try testing raw disk IO for Ivan after I have it setup. > > Yours truly, > Richard Yao >
I now have FreeBSD 9.1-BETA1 installed in a virtual machine. I noticed the following in dmesg which might explain why the emulated SCSI support is so slow: da0 at sym0 bus 0 scbus2 target 0 lun 0 da0: <QEMU QEMU HARDDISK 1.1.> Fixed Direct Access SCSI-5 device da0: 3.300MB/s transfers da0: Command Queueing enabled da0: 409600MB (838860800 512 byte sectors: 255H 63S/T 52216C) It does not explain why virtio is slow though, although I still need to test virtio against the latest code. I will do ivan's raw block test against virtio-blk, mainly because there is no point in doing it against a device whose transfers have been capped to 3.3MB/sec.
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