From: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Date: Sun, 18 Dec 2016 16:06:01 -0800 > Ok, let me try to find a way to eliminate these loads unless the application > is using shared context. > > Part of the issue is a 'backwards compatibility' feature of the processor > which loads/overwrites register 1 every time register 0 is loaded. Somewhere > in the evolution of the processor, a feature was added so that register 0 > could be loaded without overwriting register 1. That could be used to > eliminate the extra load in some/many cases. But, that would likely lead > to more runtime kernel patching based on processor level. And, I don't > really want to add more of that if possible. Or, perhaps we only enable > the shared context ID feature on processors which have the ability to work > around the backwards compatibility feature. Until the first process uses shared mappings, you should not touch the context 1 register in any way for any reason at all. And even once a process _does_ use shared mappings, you only need to access the context 1 register in 2 cases: 1) TLB processing for the processes using shared mappings. 2) Context switch MMU state handling, where either the previous or next process is using shared mappings. -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
