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[Qemu-discuss] Increasing number of threads when using ceph

From: Tyanko Aleksiev
Subject: [Qemu-discuss] Increasing number of threads when using ceph
Date: Thu, 1 Jun 2017 15:44:01 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1

Dear QEMU users,

On our OpenStack installation we use QEMU/KVM (v1:2.5 on Ubuntu 14.04, kernel 3.13) controlled by libvirt (v1.3.1). The storage back-end for the VMs is provided via ceph (v0.94.10).

Whenever a new instance is spawned the number of tasks (threads) initially started by libvirt-qemu is around 200. Big fraction of those are used to access the OSDs of the ceph cluster. Additionally, when some I/O operations are performed within the instance the number of threads will increase which is also an expected behavior.

However, we noticed is that the number of threads will never decrease over time. In particular, I generated some I/O by creating files of different size. After the write operation was completed the number of threads did not decrease. Then, I deleted the files and reclaimed (discarded/trimed) the space which again did not result in any thread being released.

I'm wondering if this is something we should expect? If not, eventually, how this issue could be addressed?

Thank you very much for your time and help!


Tyanko Aleksiev
System Administrator

Service and Support for Science IT,
University of Zurich
Winterthurerstrasse 190
CH-8057 Zurich Switzerland
Tel: +41 44 635 42 22

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