Hi Ming,
This is my cmd to run qemu:
qemu-2.12.0/x86_64-softmmu/qemu-system-x86_64 -enable-kvm -device
virtio-balloon -cpu host -smp 4 -m 2G -drive
file=/root/html/fedora-10g.img,format=raw,cache=none,aio=native,if=none,id=drive-virtio-disk1
-device virtio-blk-pci,scsi=off,drive=drive-virtio-disk1,id=virtio-disk1,bootindex=1
-drive file=/dev/sdb,format=raw,cache=none,aio=native,if=none,id=drive-virtio-disk2
-device virtio-blk-pci,scsi=off,drive=drive-virtio-disk2,id=virtio-disk2,bootindex=2
-device virtio-net,netdev=nw1,mac=00:11:22:EE:EE:10 -netdev
tap,id=nw1,script=no,downscript=no,ifname=tap0 -serial mon:stdio
-nographic -object
memory-backend-file,id=mem0,size=2G,mem-path=/dev/hugepages,share=on
-numa node,memdev=mem0 -vnc 0.0.0.0:100 -machine usb=on,nvdimm -device
usb-tablet -monitor unix:///tmp/a.socket,server,nowait -qmp
tcp:0.0.0.0:2234,server,nowait
OS image is Fedora 31. Kernel is 5.3.7-301.fc31.x86_64.
The address from virio in qemu like this:
========= size: 262144, iovcnt: 64
0: size: 4096 addr: 0x7fffc83f1000
1: size: 4096 addr: 0x7fffc8037000
2: size: 4096 addr: 0x7fffd3710000
3: size: 4096 addr: 0x7fffd5624000
4: size: 4096 addr: 0x7fffc766c000
5: size: 4096 addr: 0x7fffc7c21000
6: size: 4096 addr: 0x7fffc8d54000
7: size: 4096 addr: 0x7fffc8fc6000
8: size: 4096 addr: 0x7fffd5659000
9: size: 4096 addr: 0x7fffc7f88000
10: size: 4096 addr: 0x7fffc767b000
11: size: 4096 addr: 0x7fffc8332000
12: size: 4096 addr: 0x7fffb4297000
13: size: 4096 addr: 0x7fffc8888000
14: size: 4096 addr: 0x7fffc93d7000
15: size: 4096 addr: 0x7fffc9f1f000
They are not contiguous pages, so the pages in bvec are not continus
physical pages.
I don't know how to dump the bvec address in bio without recompiling the kernel.
IO Pattern in guest is :
root@192.168.19.239 02:39:29 ~ $ cat 256k-randread.fio
[global]
ioengine=libaio
invalidate=1
ramp_time=5
iodepth=1
runtime=120000
time_based
direct=1
[randread-vdb-256k-para]
bs=256k
stonewall
filename=/dev/vdb
rw=randread
Thanks.
Ming Lei <ming.lei@xxxxxxxxxx> 于2020年3月13日周五 上午10:32写道：
>
> On Thu, Mar 12, 2020 at 09:21:11PM +0800, Feng Li wrote:
> > Hi Ming,
> > Thanks.
> > I have tested kernel '5.4.0-rc6+', which includes 07173c3ec276.
> > But the virtio is still be filled with single page by page.
>
> Hello,
>
> Could you share your test script?
>
> BTW, it depends if fs layer passes contiguous pages to block layer.
>
> You can dump each bvec of the bio, and see if they are contiguous
> physically.
>
> Thanks,
> Ming
>
> >
> > Ming Lei <ming.lei@xxxxxxxxxx> 于2020年3月12日周四 下午8:34写道：
> > >
> > > On Thu, Mar 12, 2020 at 07:13:28PM +0800, Feng Li wrote:
> > > > Hi experts,
> > > >
> > > > May I ask a question about block layer?
> > > > When running fio in guest os, I find a 256k IO is split into the page
> > > > by page in bio, saved in bvecs.
> > > > And virtio-blk just put the bio_vec one by one in the available
> > > > descriptor table.
> > > >
> > > > So if my backend device does not support iovector
> > > > opertion(preadv/pwritev), then IO is issued to a low layer page by
> > > > page.
> > > > My question is: why doesn't the bio save multi-pages in one bio_vec?
> > >
> > > We start multipage bvec since v5.1, especially since 07173c3ec276
> > > ("block: enable multipage bvecs").
> > >
> > > Thanks,
> > > Ming
> > >
> >
>
> --
> Ming
>
