Re: 4.2.1: Poor write performance for DomU.

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

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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:

Version  1.96       ------Sequential Output------ --Sequential Input- 
--Random-
Concurrency   1     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- 
--Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP 
/sec %CP
zeus.crc.id.au   2G   658  97 54893   9 40845  10  1056  97 280453  33 
561.2  13
Latency             27145us     426ms     257ms   31900us   24701us 
222ms
Version  1.96       ------Sequential Create------ --------Random 
Create--------
zeus.crc.id.au      -Create-- --Read--- -Delete-- -Create-- --Read--- 
-Delete--
               files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP 
/sec %CP
                  16 19281  52 +++++ +++ +++++ +++ 24435  66 +++++ +++ 
+++++ +++
Latency             22860us     182us     706us   14803us      28us 
300us


Still around 50Mb/sec - so this doesn't seem to be a regression, but 
something else?


>> ~50Mb/sec write, ~267Mb/sec read. Not so awesome.
>
> We are currently working on improving the speed of pv block drivers, I
> will look into this difference between the read/write speed, but I would
> guess this is due to the size of the request/ring.

I would assume this would be in the DomU kernel?

-- 
Steven Haigh

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


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