Hi again, I've done some graphs for your perusal. The reason an adaptive strategy (such as that which I already proffered) must be used is quite simple: there's no way of knowing, in advance, how long a thread must send itself to sleep for. Windows provides only two choices for yielding: Return immediately if nothing else is to be done (Sleep(0)/SwitchToThread()). Return in 20ms, even if another process was scheduled, ran, and potentially freed us in the meantime (Sleep(1)). For forced-process-switches of frequency >> 20ms, the second (Sleep(1)) is an acceptable yield strategy; made ever-so-slightly better by checking first whether another process can be scheduled in the meantime and early exiting if so (ala Check strategy). It works effectively when there are fewer cores than processes which can work. Unfortunately, this becomes far from optimal for forced-process-switches of frequency < 20ms, especially when the number of cores becomes >= the number of processes that can work. This is because a process, having determined that it cannot continue, must decide how to yield. Assuming it's symbiotic counterpart is running on a different core and that no other work needs to be done on the system, Sleep(0) will return immediately and SwitchToThread will return immediately stating that no other processes could be scheduled. Sleep(1) will return only after 20ms. Assuming the symbiotic counterpart completes after, say, 200us, then the slowdown factor will be around 99% for any strategy that involves Sleep(1); therefore such a call needs to be made only once it is probable that the symbiotic counterpart will complete after another 20ms. My proposal attempts to implement such a strategy. As well as the attached graph, I attached the numbers from my benchmarking. The job was an iterative summation of random numbers. The benchmarking code is attached. These numbers are not extremely precise as I wasn't in a pristine environment, but they serve to illustrate. Gav 2011/8/20 Ion Gaztañaga <igaztanaga@gmail.com>:
El 20/08/2011 1:39, Ion Gaztañaga escribió:
Gav Wood (thanks!) has proposed
Obviously, I wanted to write Mathias!
Best,
ion _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost