No, userspace/kernel transitions are always and will always be slow. Every time it happens you've got to do a context switch which is super-expensive + cache unfriendly. You also pay a penalty keeping the kernel mapped at all times in terms of more pressure on the TLB but due to Spectre and Meltdown mitigations the kernel has actually been unmapped hurting the performance of switching into kernel further although this will be undone eventually.