Re: [Qemu-devel] [RFC] block io lost in the guest , possible related to qemu?

[Jack Wang]

On 10/30/2013 10:50 AM, Stefan Hajnoczi wrote:
> On Fri, Oct 25, 2013 at 05:01:54PM +0200, Jack Wang wrote:
>> We've seen guest block io lost in a VM.any response will be helpful
>>
>> environment is:
>> guest os: Ubuntu 1304
>> running busy database workload with xfs on a disk export with virtio-blk
>>
>> the exported vdb has very high infight io over 300. Some times later a
>> lot io process in D state, looks a lot requests is lost in below storage
>> stack.
> 
> Is the image file on a local file system or are you using a network
> storage system (e.g. NFS, Gluster, Ceph, Sheepdog)?
> 
> If you run "vmstat 5" inside the guest, do you see "bi"/"bo" block I/O
> activity?  If that number is very low or zero then there may be a
> starvation problem.  If that number is reasonable then the workload is
> simply bottlenecked on disk I/O.
> 
> virtio-blk only has 128 descriptors available so it's not possible to
> have 300 requests pending at the virtio-blk layer.
> 
> If you suspect QEMU, try building qemu.git/master from source in case
> the bug has already been fixed.
> 
> If you want to trace I/O requests, you might find this blog post on
> writing trace analysis scripts useful:
> http://blog.vmsplice.net/2011/03/how-to-write-trace-analysis-scripts-for.html
> 
> Stefan
> 
Thanks Stefan for your valuable input.

The image is on device exported with InfiniBand srp/srpt.
Will follow your suggestions to do further investigation.

The 300 infight ios I memtioned is from the /proc/diskstats  Field  9 --
# of I/Os currently in progress.

Jack