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For the purposes of this discussion, how do you define a 'swap' operation? Are the operands on the same cache line, or different cache lines? Is the working area warm as far as the page tables are concerned?
Regards, Dan On Tue, Jul 7, 2009 at 1:31 PM, Lyon Shinseky <lyon.shinseky@xxxxxxxxx> wrote:
Hi,
I'm measuring the miss penalty of swapping 4 bytes, 16 bytes, 64 bytes, 256 bytes, 1024 bytes and 8192 bytes on ruby. I have a code which simply swaps these bytes to measure the ruby cycles taken when this data is not in ruby cache. With 4 bytes, the cycles/(user misses) is 347 cycles which is close to my memory latency (300 cycles). With 16 bytes , this goes upto 392 cycles. With 256 bytes, this goes upto 677 cycles and with 8192 bytes , this is 1200 cycles. I'm unable to reason about the penalty increasing as I increase the number of bytes to swap. My expectation is that it should remain around 350 cycles . . . any thoughts ?
Lyon
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