Re: [Xenomai] Performance impact after switching from 2.6.2.1 to 2.6.4

[Wolfgang Netbal <wolfgang.netbal@sigmatek.at>]

Am 2016-06-01 um 16:12 schrieb Gilles Chanteperdrix:
> On Wed, Jun 01, 2016 at 03:52:06PM +0200, Wolfgang Netbal wrote:
>>
>> Am 2016-05-31 um 16:16 schrieb Gilles Chanteperdrix:
>>> On Tue, May 31, 2016 at 04:09:07PM +0200, Wolfgang Netbal wrote:
>>>> Dear all,
>>>>
>>>> we have moved our application from "XENOMAI 2.6.2.1 + Linux 3.0.43" to
>>>> "XENOMAI 2.6.4. + Linux 3.10.53". Our target is an i.MX6DL. The system
>>>> is now up and running and works stable. Unfortunately we see a
>>>> difference in the performance. Our old combination (XENOMAI 2.6.2.1 +
>>>> Linux 3.0.43) was slightly faster.
>>>>
>>>> At the moment it looks like that XENOMAI 2.6.4 calls
>>>> xnpod_schedule_handler much more often then XENOMAI 2.6.2.1 in our old
>>>> system.  Every call of xnpod_schedule_handler interrupts our main
>>>> XENOMAI task with priority = 95.
>>>>
>>>> I have compared the configuration of both XENOMAI versions but did not
>>>> found any difference. I checked the source code (new commits) but did
>>>> also not find a solution.
>>> Have you tried Xenomai 2.6.4 with Linux 3.0.43 ? In order to see
>>> whether it comes from the kernel update or the Xenomai udpate?
>> I've tried Linux 3.0.43 with Xenomai 2.6.4 an there is no difference to
>> Xenomai 2.6.2.1
>> Looks like there is an other reason than Xenomai.
> Ok, one thing to pay attention to on imx6 is the L2 cache write
> allocate policy. You want to disable L2 write allocate on imx6 to
> get low latencies. I do not know which patches exactly you are
> using, so it is difficult to check, but the kernel normally displays
> the value set in the L2 auxiliary configuration register, you can
> check in the datasheet if it means that L2 write allocate is
> disabled or not. And check if you get the same value with 3.0 and
> 3.10.
Thank you for this hint, I looked around in the kernel config, but cant 
find
an option sounds like L2 write allocate.
The only option I found was CACHE_L2X0 and that is activated on both 
kernels.
Do you have an idea whats the name of this configuration or where in the
kernel sources it should be located, so I can find out whats the name of 
the
config flag by searching the sourcecode.