MSR_SPE - being turned off...

[Morrison, Tom]

Sorry, let me try again...

>> -----Original Message-----
After sitting with the developer of the application for a while, 

a) Alignment (aka: alignment exceptions) - Looking at how it 
    handles the instruction - it interprets these SPE as common
	   instructions & then resets the 'upper' 32bits.

 	   I was just made aware that on 9/14/2007 - Kumar submitted a
         patch that handles these instructions correctly (we don't
         have that version - I am in the process of trying to port it 
	   to my current version of the kernel (to see if part of
problem).

 	   In general, this is a VERY disturbing thing. We 'turn on 
         SPE' in the compiler (-mspe=yes)(a). We are NOT explicitly 
         using SPE instructions in our application(b), BUT(c), the
4.2.171
         compiler (having origins from Code Sourcery (via Freescale))
upon
         optimizations put SPE instructions in without any regard for 
          alignment (which instead of making the code faster - might
actually
          make the code slower)? It's a little disturbing to me.

    Stay tuned for more details about my port - and seeing if some
    of my problems go away..

b) We still contend if you have multiple tasks using a (VERY) high 
Density of SPE instructions - and the system is taxed heavily
    (with lots of context switches) - there is the possibility that
    a task will get unlucky and the registers setup will NOT there 
    after the context switches back (if some other task does something
    else with the entire 64bits).



Tom

>> 
>> >> -----Original Message-----
>> >> From: Kumar Gala [mailto:galak at kernel.crashing.org]
>> >> Sent: Wednesday, May 06, 2009 8:44 AM
>> >> To: Morrison, Tom
>> >> Cc: Michael Neuling; linuxppc-dev at ozlabs.org
>> >> Subject: Re: MSR_SPE - being turned off...
>> >>
>> >> Can you describe the # of processes you are running in your test.
Is
>> >> it possible for you to try the tests w/2.6.29 from kernel.org?
>> >>
>> >> - k
>> >>
>> >> On May 6, 2009, at 7:42 AM, Morrison, Tom wrote:
>> >>
>> >> > I'm sorry I forgot to put that, this issue was found with our
>> >> > currently running kernel 2.6.23.final (what comes with the
>> >> > Freescale LTIB BSP package dated 05/23/2009).
>> >> >
>> >> > I am sorry if I don't understand your statement that the SMP
might
>> >> > be broken on this kernel, because I tried to analyze the kernel
that
>> >> > came with the latest BSP LTIB [ackage from Freescale (dated
>> 12/18/2009
>> >> > (where we got the 4.2.171 compiler from)), and the associated
>> 'switch
>> >> > context' code is exactly the same. Unfortunately, I have not
started
>> >> > the process of porting my current platform's BSP to this new
kernel
>> -
>> >> > otherwise, I would have done the test on that platform (this
also
>> >> > requires a new version of u-boot in order to test correctly))..
>> >> >
>> >> > I may have mis-interpreted something and/or I am sure I don't
>> >> > understand everything about the SMP resource management (and
>> >> > associated SPE management), so thank you for any insight you
>> >> > may have on this front...
>> >> >
>> >> > Tom
>> >> >
>> >> >>> -----Original Message-----
>> <snip other emails>