Dirk Behme wrote:

Hi Hui,

On 14.08.2012 03:46, Hui Wang wrote:

quoted

Will Deacon wrote:

quoted

On Mon, Aug 13, 2012 at 10:11:37AM +0100, Hui Wang wrote:
 

quoted

Hi Will Deacon,
    

Hello,

 

quoted

For SMP platforms, each CPU core has an independent PMU, and each 
PMU has a dedicated irq (SPI or PPI). Current perf subsystem 
framework only supports each PMU to have a dedicated SPI irq, and 
it will support each PMU to have a PPI irq (i have seen someone has 
sent out the patches), but there is a situation the subsystem 
doesn't support yet, the situation is multi PMUs share one same SPI 
irq, e.g. the i.MX6Quad CPU has 4 cortex-a9 cores, each core has a 
PMU, all PMU irqs are routed (ORed) to one SPI irq, do you know how 
to support this situation?
    

That's what I like to call a braindead, broken system. Seriously, 
CPU PMU
interrupts *can only* be handled on the CPU which raised them -- 
ORing these
things together means ping-ponging the interrupt affinity around 
until we
find the right guy. There's also the fun case where multiple PMUs 
assert
simultaneously and I've even heard about platforms where they OR in the
bloody L2 PMU interrupt as well for good measure!

If you have to support such a device, take a look at the ux500 code
(db8500_pmu_handler), but please take all of your profiling numbers 
with a
pinch of salt. For a quad-core processor, the numbers will probably 
be even
less accurate.

Also, please go ahead and inflict sufficient injuries to your 
hardware guys
that they stop this madness!
  

Got it, thanks for the information, it is very useful.

Above you mention the the i.MX6Quad CPU.

Have you done any work/patches for the i.MX6Quad PMU to work with the 
ORed PMU irq?

Not yet. i implement a pmu_handler similar to db8500_pmu_handler, but it 
can't work stable on the imx6q. With the increasing number of cpu cores, 
the situation is worse.

Have you talked with the Freescale hardware guys "that they stop this 
madness"?

As Shawn said, this issue has been reported to FSL.


Regards,
Hui.

We are facing some issues using perf top on the i.MX6Quad:

http://www.spinics.net/lists/arm-kernel/msg227042.html

Many thanks and best regards

dirk