Re: [Xen-users] File-based domU - Slow storage write since xen 4.8

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Jul 17, 2017 at 05:40:55PM +0200, Benoit Depail wrote:
> On 07/17/17 14:49, Roger Pau Monné wrote:
> > On Mon, Jul 17, 2017 at 11:11:20AM +0200, Benoit Depail wrote:
> > In order to try to figure out the problem, can you try Xen 4.9 with
> > Linux kernel 3.16?
> > 
> 
> Good call !
> 
> So, with this configuration :
> 
> dom0# xl info
> host                   : ikea
> release                : 3.16.0-4-amd64
> version                : #1 SMP Debian 3.16.43-2 (2017-04-30)
> machine                : x86_64
> nr_cpus                : 24
> max_cpu_id             : 23
> nr_nodes               : 4
> cores_per_socket       : 12
> threads_per_core       : 1
> cpu_mhz                : 2200
> hw_caps                :
> 178bf3ff:80802001:efd3fbff:000837ff:00000000:00000000:00000000:00000100
> virt_caps              : hvm
> total_memory           : 49147
> free_memory            : 45572
> sharing_freed_memory   : 0
> sharing_used_memory    : 0
> outstanding_claims     : 0
> free_cpus              : 0
> xen_major              : 4
> xen_minor              : 8
> xen_extra              : .1
> xen_version            : 4.8.1
> xen_caps               : xen-3.0-x86_64 xen-3.0-x86_32p hvm-3.0-x86_32
> hvm-3.0-x86_32p hvm-3.0-x86_64
> xen_scheduler          : credit
> xen_pagesize           : 4096
> platform_params        : virt_start=0xffff800000000000
> xen_changeset          :
> xen_commandline        : dom0_mem=2G,max:2G dom0_max_vcpus=2 dom0_vcpus_pin
> cc_compiler            : gcc (Debian 6.3.0-16) 6.3.0 20170425
> cc_compile_by          : ian.jackson
> cc_compile_domain      : eu.citrix.com
> cc_compile_date        : Tue May  2 14:06:04 UTC 2017
> build_id               : 0b619fa14fca0e6ca76f2a8b52eba64d60aa37de
> xend_config_format     : 4
> 
> The writing performances are the same in the dom0 and in the domU.
> 
> In the mean time I found that the problem is not NFS specific so I'll
> stick to raw image files on the local disks, to keep things simple.
> 
> I'll see if I can roughly pinpoint the kernel version that trigger this
> behaviour.
> 
> Thanks _a lot_ for your help. This is a good enough work around for us,
> so we can start extensive testing to get xen 4.8 in production.

There are not a huge amount of changes to blkback, so it would be
helpful if you could pinpoint the change that introduced this
regression for you, or if you can get a kernel version that introduced
the regression that would also be helpful.

Thanks, Roger.

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