On 22/06/16 08:07, Torsten Bonde Christiansen wrote: > On 2016-06-22 09:02, LacaK wrote: >> Hi *, >> >> may be that this question is bit off-topic here, but I am sure, that here >> are experts, which know answer ;-) >> >> I have simple Lazarus/FPC application (with no explicit threads) which does >> intensive calculations (local thresholding with big window size) on image, >> which is stored into memory as 2D byte array. >> (so only memory access is done and some integer calculations) >> >> When I run this application and look at Task Manager or Resource Monitor I >> see, that all 4 cores "are used" (at least performance graph shows usage or >> in other words activity in graph increasees) >> Total CPU usage is <= 25% (which points out to fact, that only 1/4 cores is >> used) >> >> Why this ? As far as I expect, that single threaded application should use >> only one core, so I would expect activity only on one core not on all four >> cores >> (I know that in theory CPU can switch single thread between cores, but I >> doubt that this is case (as switching has extra cost)... or is ?) > > Nailed it right there.... > > All modern CPU automatically swaps running threads (unless affinity is set) > to other cores in case there is a high load. This is done from a
^^^^^^^^^^^^^^^^^ s/CPU/OS Kernel ;) > heat perspective, since running on a single cores will make a local heat spot > on the dye - a things which is not prefered and also not really > cost effient. > >> (Btw: When I set affinity to only one core, then this core is 100% and >> others are 0% as expected) >> > > -Torsten. -L. _______________________________________________ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
