The kernel does use PAUSE // f390
objdump -d vmlinux.o | grep -c "f3 90"
245
e.g.
00000000000683a0 <__task_rq_lock>:
683a0: e8 00 00 00 00 callq 683a5 <__task_rq_lock+0x5>
683a5: 55 push %rbp
683a6: 48 89 e5 mov %rsp,%rbp
683a9: 41 56 push %r14
683ab: 49 c7 c6 00 00 00 00 mov $0x0,%r14
683b2: 41 55 push %r13
683b4: 49 89 fd mov %rdi,%r13
683b7: 41 54 push %r12
683b9: 53 push %rbx
683ba: 48 c7 c3 00 00 00 00 mov $0x0,%rbx
683c1: 41 8b 45 3c mov 0x3c(%r13),%eax
683c5: 4d 8b 24 c6 mov (%r14,%rax,8),%r12
683c9: 49 01 dc add %rbx,%r12
683cc: 4c 89 e7 mov %r12,%rdi
683cf: e8 00 00 00 00 callq 683d4 <__task_rq_lock+0x34>
683d4: 41 8b 45 3c mov 0x3c(%r13),%eax
683d8: 49 8b 14 c6 mov (%r14,%rax,8),%rdx
683dc: 48 01 da add %rbx,%rdx
683df: 49 39 d4 cmp %rdx,%r12
683e2: 75 13 jne 683f7 <__task_rq_lock+0x57>
683e4: 41 83 7d 60 02 cmpl $0x2,0x60(%r13)
683e9: 74 0c je 683f7 <__task_rq_lock+0x57>
683eb: 5b pop %rbx
683ec: 4c 89 e0 mov %r12,%rax
683ef: 41 5c pop %r12
683f1: 41 5d pop %r13
683f3: 41 5e pop %r14
683f5: 5d pop %rbp
683f6: c3 retq
683f7: 4c 89 e7 mov %r12,%rdi
683fa: e8 00 00 00 00 callq 683ff <__task_rq_lock+0x5f>
683ff: 41 83 7d 60 02 cmpl $0x2,0x60(%r13)
68404: 75 bb jne 683c1 <__task_rq_lock+0x21>
68406: f3 90 pause
68408: 41 83 7d 60 02 cmpl $0x2,0x60(%r13)
6840d: 75 b2 jne 683c1 <__task_rq_lock+0x21>
6840f: eb f5 jmp 68406 <__task_rq_lock+0x66>
68411: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
68416: 66 2e 0f 1f 84 00 00 nopw %cs:0x0(%rax,%rax,1)
6841d: 00 00 00
while (unlikely(task_on_rq_migrating(p)))
cpu_relax();
-ss