2016-08-19 23:30 GMT+08:00 Morten Rasmussen <morten.rasmus...@arm.com>: > Hi Steve, > > On Thu, Aug 18, 2016 at 06:55:41PM -0700, Steve Muckle wrote: >> PELT scales its util_sum and util_avg values via >> arch_scale_cpu_capacity(). If that function is passed the CPU's sched >> domain then it will reduce the scaling capacity if SD_SHARE_CPUCAPACITY >> is set. PELT does not pass in the sd however. The other caller of >> arch_scale_cpu_capacity, update_cpu_capacity(), does. This means >> util_sum and util_avg scale beyond the CPU capacity on SMT. >> >> On an Intel i7-3630QM for example rq->cpu_capacity_orig is 589 but >> util_avg scales up to 1024. > > I can't convince myself whether this is the right thing to do. SMT is a > bit 'special' and it depends on how you model SMT capacity. > > I'm no SMT expert, but the way I understand the current SMT capacity > model is that capacity_orig represents the capacity of the SMT-thread > when all its thread-siblings are busy. The true capacity of an > SMT-thread where all thread-siblings are idle is actually 1024, but we > don't model this (it would be nightmare to track when the capacity > should change). The capacity of a core with two or more SMT-threads is > chosen to be 1024 + smt_gain, where smt_gain is supposed represent the > additional throughput we gain for the additional SMT-threads. The reason > why we don't have 1024 per thread is that we would prefer to have only > one task per core if possible.
Agreed, maybe the capacity of an SMP-thread where all thread-siblings are idle can be 1024 + smt_gain after latest IA technology. http://www.intel.com/content/www/us/en/architecture-and-technology/turbo-boost/turbo-boost-max-technology.html Regards, Wanpeng Li
