On Mon, Oct 26, 2020 at 10:08:47AM -0700, psodagud@xxxxxxxxxxxxxx wrote: > On 2020-10-23 14:59, Thomas Gleixner wrote: > > On Thu, Oct 22 2020 at 15:04, Elliot Berman wrote: > > > In a heterogeneous multiprocessor system, specifying the 'maxcpus' > > > parameter on kernel command line does not provide sufficient control > > > over which CPUs are brought online at kernel boot time, since CPUs may > > > have nonuniform performance characteristics. Thus, add bootcpus kernel > > > parameter to control which CPUs should be brought online during kernel > > > boot. When both maxcpus and bootcpus is set, the more restrictive of > > > the > > > two are booted. > > > > What for? 'maxcpus' is a debug hack at best and outright dangerous on > > certain architectures. Why do we need more of that? Just let the machine > > boot and offline the CPUs from user space. > > Hi Thomas and Peter, > > Based on my understanding with maxcpus option provides, maximum no of CPUs > are brough up during the device boot up. There is a different case, in which > we want to restrict which CPUs to be brough up. > On a system with 8 cpus, if we set maxcpus as 3, cpu0, cpu1, and cpu2 are > brough up during the bootup. For example, if we want to bring core0, core3 > and core4 current maxcpu(as 3) setting would not help us. > On some platform we want the flexibility on which CPUs to bring up during > the device bootup. bootcpus command line is helping to bring specific CPUs > and these patches are working downstream. That's a lot of words, but exactly 0 on _WHY_ you would want to do that.
