[Xen-devel] Does tapdisk2 dispatch requests from different DomUs?

[Yuehai Xu <yuehaixu@xxxxxxxxx>]

Hi All,

Suppose there are two DomUs, and each one has a corresponding tapdisk2
process to dispatch requests. Theoretically, different tapdisk should
only dispatch requests from its corresponding DomU. However, I notice
that a certain tapdisk would dispatch requests from other DomUs, is it
normal?

Below is the background:
Dom1.cfg:
kernel="/boot/vmlinuz-2.6.31.13-xen-guest_32bit_ubuntu"
name = "dom1"
vif  = ['mac=00:1A:2A:4A:6A:8A, bridge=xenbr0, ip=192.168.1.111']
disk = ['tap2:aio:/guest_os/dom1/img,xvda1,w',
'tap2:aio:/guest_os/dom1/swap,xvda2,w',
'tap2:aio:/mnt/sdb1/xen/img,xvdc,w']
root = "/dev/xvda1"
extra = "fastboot enforcing=0 console=hvc0"

Dom2.cfg:
kernel="/boot/vmlinuz-2.6.31.13-xen-guest_32bit_ubuntu"
name = "dom2"
vif  = ['mac=00:1B:2B:4B:6B:8B, bridge=xenbr0, ip=192.168.1.112']
disk = ['tap2:aio:/guest_os/dom2/img,xvda1,w',
'tap2:aio:/guest_os/dom2/swap,xvda2,w',
'tap2:aio:/mnt/sdb7/xen/img,xvdb,w']
root = "/dev/xvda1"
extra = "fastboot enforcing=0 console=hvc0"

ps -ef | grep tapdisk | grep sdb :
root      7225     1  0 09:51 ?        00:00:18 /usr/sbin/tapdisk2 -n
aio:/mnt/sdb7/xen/img
root      8670     1  0 10:13 ?        00:00:00 /usr/sbin/tapdisk2 -n
aio:/mnt/sdb1/xen/img

When I run postmark which creates small random writes in both Doms,
each tapdisk dispatches requests both from Dom1 and Dom2. In this way,
it is impossible to do QoS for disk I/O since it will never be known
which requests are from which DomUs. Is this a known problem or is
there something wrong that I have done?

I appreciate your help.

Thanks,
Yuehai

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