On Thu, Nov 29, 2018 at 09:50:13AM -0500, Konrad Rzeszutek Wilk wrote: > On Thu, Nov 29, 2018 at 09:42:56AM -0500, Konrad Rzeszutek Wilk wrote: > > On Sun, Nov 25, 2018 at 07:33:36PM +0100, Thomas Gleixner wrote: > > > Currently the 'sched_smt_present' static key is enabled when at CPU > > > bringup > > > SMT topology is observed, but it is never disabled. However there is > > > demand > > > to also disable the key when the topology changes such that there is no > > > SMT > > > present anymore. > > > > > > Implement this by making the key count the number of cores that have SMT > > > enabled. > > > > > > In particular, the SMT topology bits are set before interrrupts are > > > enabled > > > and similarly, are cleared after interrupts are disabled for the last time > > > and the CPU dies. > > > > I see that the number you used is '2', but I thought that there are some > > CPUs out there (Knights Landing?) that could have four threads?
This code is generic, Sparc, Power and I think MIPS all have parts with SMT8. > > Would it be better to have a generic function that would provide the > > amount of threads the platform does expose - and use that instead > > of a constant value? > > Nevermind - this would work even with 4 threads as we would hit the > number '2' before '4' and the key would be turned on/off properly. Indeed so, 2 is the point where we either have more than 1 sibling, or will go back to 1.
