[libvirt] increase number of libvirt threads by starting tansient guest doamin - is it a bug?

[ustermann78 at web.de]

Hi Michal,
thank you for your answer.
so if i understand that correctly, no matter if i shutdown or destroy the domain and no matter if it is a transient or an persistent vm, the thread should disappear, right?

in my case they still exist, also an hour after i destroy the domain (and don´t start any new one).

i use libvirt-1.1.35 on fedora core 20, for information.

all the best
max
 
 

Gesendet: Freitag, 26. September 2014 um 11:21 Uhr
Von: "Michal Privoznik" <mprivozn at redhat.com>
An: ustermann78 at web.de, libvir-list at redhat.com, libvirt-users at redhat.com
Betreff: Re: [libvirt] increase number of libvirt threads by starting tansient guest doamin - is it a bug?
On 26.09.2014 09:46, ustermann78 at web.de wrote:
> hello,
>
> if i start a transient guest doamin via "virsh create abcd.xml" i see an additional libvirt thread and also some open files:
>
> pstree -h `pgrep libvirtd`
> libvirtd───11*[{libvirtd}]
>
> libvirtd 3016 root 21w REG 253,0 6044 1052094 /var/log/libvirt/libxl/abcd.log
> libvirtd 3016 root 22r FIFO 0,8 0t0 126124 pipe
> libvirtd 3016 root 23w FIFO 0,8 0t0 126124 pipe
> libvirtd 3016 root 24u REG 0,37 0 4 /proc/xen/privcmd
> libvirtd 3016 root 25u unix 0xffff8807d2c3ad80 0t0 126125 socket
> libvirtd 3016 root 26r FIFO 0,8 0t0 126127 pipe
> libvirtd 3016 root 27w FIFO 0,8 0t0 126127 pipe
> libvirtd 3016 root 28r FIFO 0,8 0t0 124783 pipe
> libvirtd 3016 root 29w FIFO 0,8 0t0 124783 pipe
> libvirtd 3016 root 30r FIFO 0,8 0t0 127140 pipe
> libvirtd 3016 root 31w FIFO 0,8 0t0 127140 pipe
>
> if i destroy these vm via "virsh destroy abcd", i see that the additional thread still exists and also the list of openfiles is the same.
> if i start the transient guest domain again, i observe an increase in the number of libvirt threads ans also in the list of openfiles:
>
> [root at localhost libxl]# pstree -h `pgrep libvirtd`
> libvirtd───12*[{libvirtd}]
>
> libvirtd 3016 root 21w REG 253,0 13783 1052094 /var/log/libvirt/libxl/abcd.log
> libvirtd 3016 root 22r FIFO 0,8 0t0 126124 pipe
> libvirtd 3016 root 23w FIFO 0,8 0t0 126124 pipe
> libvirtd 3016 root 24u REG 0,37 0 4 /proc/xen/privcmd
> libvirtd 3016 root 25u unix 0xffff8807d2c3ad80 0t0 126125 socket
> libvirtd 3016 root 26r FIFO 0,8 0t0 126127 pipe
> libvirtd 3016 root 27w FIFO 0,8 0t0 126127 pipe
> libvirtd 3016 root 28r FIFO 0,8 0t0 124783 pipe
> libvirtd 3016 root 29w FIFO 0,8 0t0 124783 pipe
> libvirtd 3016 root 30r FIFO 0,8 0t0 127140 pipe
> libvirtd 3016 root 31w FIFO 0,8 0t0 127140 pipe
> libvirtd 3016 root 32w REG 253,0 13783 1052094 /var/log/libvirt/libxl/abcd.log
> libvirtd 3016 root 33r FIFO 0,8 0t0 129039 pipe
> libvirtd 3016 root 34w FIFO 0,8 0t0 129039 pipe
> libvirtd 3016 root 35u REG 0,37 0 4 /proc/xen/privcmd
> libvirtd 3016 root 36u unix 0xffff8807d398bb80 0t0 129040 socket
> libvirtd 3016 root 37r FIFO 0,8 0t0 129042 pipe
> libvirtd 3016 root 38w FIFO 0,8 0t0 129042 pipe
> libvirtd 3016 root 39r FIFO 0,8 0t0 129043 pipe
> libvirtd 3016 root 40w FIFO 0,8 0t0 129043 pipe
> libvirtd 3016 root 41r FIFO 0,8 0t0 129044 pipe
> libvirtd 3016 root 42w FIFO 0,8 0t0 129044 pipe
>
> if i destroy the doamin again and define them via "virsh define abcd.xml" and start them then via "virsh start abcd", the number of libvirtd threads don´t increase again and also the number of open files is the same.
>
> My question: is it normal that for transient guest domains the created libvirtd thread sill exists and also the open files after i destroy the doamin? or is it bug?


The thread is created as a result of this commit:

commit 03b3f8940af1a3179b7d5e19b25f54290bde10e0
Author: Jim Fehlig <jfehlig at suse.com>
AuthorDate: Fri Jan 31 23:06:35 2014 -0700
Commit: Jim Fehlig <jfehlig at suse.com>
CommitDate: Thu Feb 6 10:17:58 2014 -0700

libxl: handle domain shutdown events in a thread

Handling the domain shutdown event within the event handler seems
a bit unfair to libxl's event machinery. Domain "shutdown" could
take considerable time. E.g. if the shutdown reason is reboot,
the domain must be reaped and then started again.

Spawn a shutdown handler thread to do this work, allowing libxl's
event machinery to go about its business.

Signed-off-by: Jim Fehlig <jfehlig at suse.com>



Which was then modified by 0a840e23 (pure code movement). The thing is,
libvirt listens on events from hypervisors. And some actions that are
taken subsequently may take ages to finish. However, the events are
executed single threaded, so they serialize effectively. And for the
long lasting actions (like shutdown, in fact in libxl shutdown only) a
new thread is spawned so the event loop is not burdened for too long.
The thread is created with 'detach-state' attribute so once the shutdown
is handled the thread should just disappear.

Michal