Extrinsic and Intrinsic Text Cloning

Abstract

Text Cloning occurs when a processor is storing in one or more levels of its cache hierarchy the same text multiple times. There are several causes of Text Cloning and we classify them either as Extrinsic or Intrinsic.Extrinsic Text Cloning can happen due to user and software practices, or middleware policies, which result into making multiple copies of a binary and concurrently executing the multiple copies on the same processor.Intrinsic Text Cloning can happen when an instruction cache is Virtually Indexed/Virtually Tagged and the process identifier is included in the tag. A simultaneous multithreaded processor, that employs such cache, will map the text of concurrent processes of the same binary to different instruction cache space due to their distinct process identifier.Text cloning can be wasteful to performance, especially for simultaneous multithreaded processors, because concurrent processes compete for cache space to store the same instruction blocks. Experimental results on simultaneous multithreaded processors indicate that the performance overhead of this type of undesirable cloning is significant. Theses findings call for OS and/or architectural support to reduce or eliminate Text Cloning.