Re: [Xen-devel] Load increase after memory upgrade (part2)

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 18.01.12 at 12:28, Pasi KÃrkkÃinen<pasik@xxxxxx> wrote:
> On Tue, Jan 17, 2012 at 04:02:25PM -0500, Konrad Rzeszutek Wilk wrote:
>> > 
>> > And the devices do work ... so how does that work ...
>> 
>> Most (all?) drivers are written to work with bounce-buffering.
>> That has never been a problem.
>> 
>> The issue as I understand is that the DVB drivers allocate their buffers
>> from 0->4GB most (all the time?) so they never have to do bounce-buffering.
>> 
>> While the pv-ops one ends up quite frequently doing the bounce-buffering, 
> which
>> implies that the DVB drivers end up allocating their buffers above the 4GB.
>> This means we end up spending some CPU time (in the guest) copying the 
> memory
>> from >4GB to 0-4GB region (And vice-versa).
>> 
>> And I am not clear why this is happening. Hence my thought
>> was to run an Xen-O-Linux kernel v2.6.3X and a PVOPS v2.6.3X (where X is the
>> same) with the same PCI device (and the test would entail rebooting the
>> box in between the launches) to confirm that the Xen-O-Linux is doing 
> something
>> that the PVOPS is not.
>> 
>> So far, I've haven't had much luck compiling a Xen-O-Linux v2.6.38 kernel
>> so :-(
>> 
> 
> Did you try downloading a binary rpm (or src.rpm) from OpenSuse? 
> I think they have 2.6.38 xenlinux kernel available.

openSUSE 11.4 is using 2.6.37; 12.1 is on 3.1 (and SLE is on 3.0).
Pulling out (consistent) patches at 2.6.38 level might be a little
involved.

Jan

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