Re: [Xen-devel] xen-access performance from DomU

[Bread Cutter <cutter409@xxxxxxxxx>]

I've tried upgrading DomU to Ubuntu 14.04 to get kernel
3.13.0-24-generic, since I saw some changes to the evtch module, but
it didn't make a difference. I also saw somewhere to try OpenSUSE
because of kernel support for "Suspend event channels", but I can't
find much about what those actually are. In any case, an OpenSUSE DomU
did not help.

On Fri, Apr 11, 2014 at 12:21 PM, Bread Cutter <cutter409@xxxxxxxxx> wrote:
> By the way, this is with Xen-4.4 (although I had the same issue on
> 4.3), running Ubuntu 13.10 Saucy with kernel 3.11.0-19-generic.
>
> On Thu, Apr 10, 2014 at 6:42 PM, Bread Cutter <cutter409@xxxxxxxxx> wrote:
>> Hello all,
>>
>> I'm having a performance issue with the xen-access API from DomU.
>>
>> First of all, I've changed xen/include/xsm/dummy.h so that all
>> permissions are allowed. This is temporary and for testing, simply so
>> that I could run xen-access from DomU. I've also changed
>> tools/tests/xen-access/xen-access.c (patch attached) so that I monitor
>> cr3 writes. This was just something that happens consistently enough
>> for comparing performance. The actual value of cr3 isn't important for
>> my testing.
>>
>> When I run xenaccess in Dom0, the target HVM domain runs pretty
>> smoothly. I can launch programs and Windows feels pretty responsive.
>>
>> However, when I run the same tool from a PV-DomU, the target domain
>> becomes extremely sluggish. Launching a web browser takes a long time,
>> for example, and it's essentially unusable.
>>
>> Can anyone offer any insight, and/or a remedy?
>>
>> Thank you!

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