[pve-devel] Default cache mode for VM hard drives

[Stanislav German-Evtushenko]

On Thu, May 28, 2015 at 6:47 PM, Dietmar Maurer <dietmar at proxmox.com> wrote:
>> > But there is currently only one io-thread in qemu, so this
>> > cannot happen with qemu if above is the only problem?
>>
>> But there are other threads, right? Buffer can be changed by another
>> thread where guest OS itself is running.
>
> No, AFAIK there is only one thread doing all IO (currently). But it
> is using async IO with coroutines - maybe that can also trigger the
> problem?
>

Please have a look:

root at virt1:~# for pid in $(pidof kvm); do echo "threads of $pid $(ps
-o nlwp $pid | tail -1)"; done
threads of 900883    6
threads of 606008    5
threads of 524867    4
threads of 524750    5
threads of 524550    7
threads of 521471    8
threads of 520324    4
threads of 519520    3
threads of 518997    4
threads of 152071    4
threads of 9029    3
threads of 8874    4
threads of 8695    3
threads of 8471    3

root at virt1:~# for pid in $(pidof kvm); do echo "threads of $pid $(ps
-o nlwp $pid | tail -1)"; done
threads of 900883    6
threads of 606008    5
threads of 524867    4
threads of 524750    5
threads of 524550    7
threads of 521471    5
threads of 520324    4
threads of 519520    3
threads of 518997    3
threads of 152071    4
threads of 9029    4
threads of 8874    3
threads of 8695    3
threads of 8471    3

Each kvm process have multiple threads and the number of them is
changing in time.

Stanislav