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Re: [libvirt] [PATCH 0/7] Add more options for IOThreads

On 09/03/2014 10:15 AM, John Ferlan wrote:
> The following patches will add more support for IOThreads not completed
> from the initial patches. These changes support the remaining elements of
> bz https://bugzilla.redhat.com/show_bug.cgi?id=1101574 (working through
> unsetting the private bits - as there's nothing in there that should
> necessarily be private).
> Changes:
>  1. Add "--iothread" option to virsh attach-disk to allow using a specific
>     iothread when attaching a disk
>  2. Add the ability to set CPU affinity for an IOThread.  This involves
>     multiple steps (patches 2-6) of adding the infrastructure to support
>     setting scheduler affinity for the IOThread including cgroup setup.
>     For the most part it's a "copy" of the vCPU pinning code, but without
>     the external interfaces - those will come at a later time after RHEL7.1.
>  3. Add to <cpuset/> a new element <iothreadpin iothread='#" cpuset="string"/>
>   NOTE: I can combine any/all of patches 2-6 - I just kept them separate
>         so it wasn't a larger single patch.
> Although future changes will support API's and virsh commands to modify
> the iothreadpin, this set of changes at least is backportable to RHEL7.1
> since there are no external API changes.
> John Ferlan (7):
>   virsh: Add iothread to 'attach-disk'
>   qemu: Issue query-iothreads and to get list of active IOThreads
>   vircgroup: Introduce virCgroupNewIOThread
>   qemu_domain: Add niothreadpids and iothreadpids

Up to this patch, things worked for me,

>   qemu_cgroup: Introduce cgroup functions for IOThreads
>   qemu: Allow pinning specific IOThreads to a CPU

but with these two patches, I get a compilation failure:

qemu/qemu_cgroup.c: In function 'qemuSetupCgroupForIOThreads':
qemu/qemu_cgroup.c:1160:41: error: 'struct <anonymous>' has no member
named 'niothreadspin'
             for (j = 0; j < def->cputune.niothreadspin; j++) {
>   domain_conf: Add iothreadpin to cputune

and with this patch, I'm now unable to start a transient domain, with a
less-than-stellar message:

$ qemu-img create -f qcow2 -o compat=0.10 base.img 10M
$ virsh create /dev/stdin <<EOF
<domain type='kvm'>
 <memory unit='MiB'>256</memory>
   <type arch='x86_64'>hvm</type>
   <disk type='file' device='disk'>
     <driver name='qemu' type='qcow2'/>
     <source file='$PWD/base.img'/>
     <target dev='vda' bus='virtio'/>
   <graphics type='vnc'/>

error: Failed to create domain from /dev/stdin
error: An error occurred, but the cause is unknown

Normally, that command starts up a guest (yeah, the guest is doing
nothing but wasting CPU cycles, because it has a blank disk, but it's a
great little smoke test for my recent work in block jobs)

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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