Re: 4.2.1: Poor write performance for DomU.

[Steven Haigh <netwiz@crc.id.au>]

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On 20/02/2013 8:49 PM, Steven Haigh wrote:
> On 20/02/2013 7:49 PM, Steven Haigh wrote:
>> On 20/02/2013 7:26 PM, Roger Pau Monné wrote:
>>> On 20/02/13 03:10, Steven Haigh wrote:
>>>> Hi guys,
>>>>
>>>> Firstly, please CC me in to any replies as I'm not a subscriber these
>>>> days.
>>>>
>>>> I've been trying to debug a problem with Xen 4.2.1 where I am unable to
>>>> achieve more than ~50Mb/sec sustained sequential write to a disk. The
>>>> DomU is configured as such:
>>>
>>> Since you mention 4.2.1 explicitly, is this a performance regression
>>> from previous versions? (4.2.0 or the 4.1 branch)
>>
>> This is actually a very good question. I've reinstalled my older
>> packages of Xen 4.1.3 back on the system. Rebooting into the new
>> hypervisor, then starting the single DomU again. Ran bonnie++ again on
>> the DomU:
>>
>> Still around 50Mb/sec - so this doesn't seem to be a regression, but
>> something else?
>
> I've actually done a bit of thinking about this... A recent thread on
> linux-raid kernel mailing list about Xen and DomU throughput made me
> revisit my setup. I know I used to be able to saturate GigE both ways
> (send and receive) to the samba share served by this DomU. This would
> mean I'd get at least 90-100Mbyte/sec. What exact config and kernel/xen
> versions this was as this point in time I cannot say.
>
> As such, I had a bit of a play and recreated my RAID6 with 64Kb chunk
> size. This seemed to make rebuild/resync speeds way worse - so I
> reverted to 128Kb chunk size.
>
> The benchmarks I am getting from the Dom0 is about what I'd expect - but
> I wouldn't expect to lose 130Mb/sec write speed to the phy:/ pass
> through of the LV.
>
>  From my known config where I could saturate the GigE connection, I have
> changed from kernel 2.6.32 (Jeremy's git repo) to the latest vanilla
> kernels - currently 3.7.9.
>
> My build of Xen 4.2.1 also has all of the recent security advisories
> patched as well. Although it is interesting to note that downgrading to
> Xen 4.1.2 made no difference to write speeds.
>

Just wondering if there is any further news or tests that I might be 
able to do on this?

-- 
Steven Haigh

Email: netwiz@crc.id.au
Web: https://www.crc.id.au
Phone: (03) 9001 6090 - 0412 935 897
Fax: (03) 8338 0299


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