Future computer systems will integrate tens of multithreaded processor cores on a single chip die, resulting in hundreds of concurrent program threads sharing system resources. These designs will be the cornerstone of improving throughput in high-performance computing and server environments. However, to date, appropriate systems software (operating system, run-time system, and compiler) technologies for these emerging machines have not been adequately explored. Future processors will require sophisticated hardware monitoring units to continuously feed back resource utilization information to allow the operating system to make optimal thread co-scheduling decisions and also to software that continuously optimizes the program itself. Nevertheless, in order to continually and automatically adapt systems resources to program behaviors and application needs, specific run-time information must be collected to adequately enable dynamic code optimization and operating system scheduling. Generally, run-time optimization is limited by the time required to collect profiles, the time required to perform optimization, and the inherent benefits of any optimization or decisions. Initial techniques for effectively utilizing runtime information for dynamic optimization and informed thread scheduling in future multithreaded architectures are presented.