Itanium: Problem with "L3 cache data read" events

[defender1234]

Hi!

I use VTune to profile an application running on the Intel Itanium platform. I want to see how the cache hierarchy performs:

Strangely, I don't get any samples for the event L3_READS-DATA_READ.ALL. It's strange, because I experience a lot of L2 cache data misses, so these misses should go directly to the L3 cache in my opinion. Hence, I can't believe what vTune reports right now.

It's a very special question, so are there Itanium experts who know why vTune reports there are not L3 cache data read events? The machine I use has 2 Itanium Montecitos, with 2 x 6MB unified L3 cache each.

If you need more information, let me know.

Thanks so much in advance!

Andreas

[Peter_W_Intel]

Quoting - defender1234

Hi!

I use VTune to profile an application running on the Intel Itanium platform. I want to see how the cache hierarchy performs:

Strangely, I don't get any samples for the event L3_READS-DATA_READ.ALL. It's strange, because I experience a lot of L2 cache data misses, so these misses should go directly to the L3 cache in my opinion. Hence, I can't believe what vTune reports right now.

It's a very special question, so are there Itanium experts who know why vTune reports there are not L3 cache data read events? The machine I use has 2 Itanium Montecitos, with 2 x 6MB unified L3 cache each.

If you need more information, let me know.

Thanks so much in advance!

Andreas

Hi Andreas,

I think that you may check:

1. If your application has many memory accesses, and there are many L2D_MISSES. Since L2D cache misses happened, the request will be sent to L3 for cache read.

2. Simplywrite codeto read arrays in a long loop, like as c =a + b;"i" could be 0 to 6,000,000, array data type as double. I believe thatVTune Analyzer can capturesamples for eventL3_READS-DATA_READ.ALL

3. Sometimes samples for L3_* events are not shown - it doesn't mean this event didn't occur, go "Sampling Configure" to change "Sample After Value" (SAV) to smaller. Sampling collector will capture samples.

Regards, Peter