Generating traces with physical addresses

[Geoffrey]

 Is it possible  to generate  a trace of all the physical addresses accessed  by a single threaded application. If  yes where do I start?

--Geoffrey 

[Trevor E. Carlson]

Geoffrey,

Might I suggest that you take a look at Pin [1], a dynamic instrumentation framework. With Pin, you will be able to capture all of the virtual address accesses of your program (as you won't need the extra overhead of Sniper if all you want to do is capture addresses). If you are running Linux, you can then perform a translation with the /proc/self/pagemap file in your pintool to determine the physical addresses used by the application. Take a look at the Linux Kernel documentation [2,3] for more information on how to interpret the data in pagemap.

I hope that this helps,

Trevor

[1] http://pintool.org

[2] /usr/src/linux/Documentation/vm/pagemap.txt

[3] http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=blob;f=Documentation/vm/pagemap.txt;hb=HEAD

On Nov 7, 2012, at 6:04 PM, Geoffrey <get...@gmail.com> wrote:

 Is it possible  to generate  a trace of all the physical addresses accessed  by a single threaded application. If  yes where do I start?

--Geoffrey 

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[Qi Zeng]

Hi, Trevor,

    How can I generate traces with Physical addresses of multi-program run with sniper? As the translated address use the page table inside sniper instead of Linux. 

To make it simple, I want to collect the trace information of all L3 misses with physical address?

Thanks,

Qi

[Trevor Carlson]

Qi,

     Check the va2pa callback in the pin tool. You should be able to update the code to resolve the physical addresses when you create the trace.

Trevor

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[Qi Zeng]

Hi Trevor,

      I checked the function of Int64 TraceThread::va2pa, but I cannot find the implementation of page table.

     I wonder if we have the restriction as address space for virtual-physical address translation, like if we set the DRAM as 1GB, the translated physical address cannot exceed the range of 1GB because the memory is addressable.

Thanks,

Qi

[Trevor Carlson]

Qi,

The va2pa function goes out to Linux (/proc/self/maps) and uses the virtual to physical mappings in the system to map the addresses. This was done to allow multi-process MPI applications that use shared memory to share the same pages. The DRAM size is not set in Sniper, only the latencies, so effectively, you can have as much memory as supported by your system. We model TLB timing in Sniper, but the actual translations happen via the map file. You can setup your own mapping by changing the va2pa function to override the physical mapping of your system.

Trevor