Re: serious performance regression in Xen 4.2.4 and 4.2.5

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 19/02/15 11:08, Andreas Kinzler wrote:
> Hello Xen developers,
>
> since we use Xen for our production systems, I run many tests on Xen
> (stability/performance). One test now uncovered a serious performance
> regression when updating from Xen 4.2.3 to 4.2.x (with x>=4). To
> reproduce run a domU (HVM) and compile a kernel for example ("time
> make -j3"). Below are my results - compilation times more than double!
>
> Is it my mistake or otherwise how could such a bug be unnoticed?
> Really wondering.
> If it is really a regression, will it be fixed since the 4.2 branch is
> declared unsupported?
>
> Regards Andreas
>
> Xen 4.2.3, 3.10.44-el7-pvops0-ak3, Xeon E3-1230, compile in HVM
>     real    2m58.371s
>     user    5m11.580s
>     sys     0m12.736s
>
> Xen 4.2.4, 3.10.44-el7-pvops0-ak3, Xeon E3-1230, compile in HVM
>     real    6m44.697s    (!!!)
>     user    12m4.988s
>     sys     0m33.916s
>
> Xen 4.2.5, 3.10.44-el7-pvops0-ak3, Xeon E3-1230, compile in HVM
>     real    6m27.998s    (!!!)
>     user    11m42.664s
>     sys     0m32.700s
>
>

Is it perhaps
http://xenbits.xen.org/gitweb/?p=xen.git;a=commitdiff;h=f1e0df14412ccc6933a68eda66ac5b7d89186b62
?

There are a number of correctness fixes in that range which will
adversely affect performance.

~Andrew