On Sat, 18 Mar 2006, Parag Warudkar wrote:
>
> Here is the disassembly of cpufrequency_conservative.o:dbs_check_cpu() from my
> setup, if it is of any help.
Yup. Just confirming that this seems to be what I was pointing to.
It's the first "for_each_online_cpu()" loop: the reason it's pretty far
down in the function disassembly is that the early "init_flag == 0" test
jumps off into the latter part of the thing, even though the code is
early. That's just gcc re-ordering stuff.
> 000004b0 <dbs_check_cpu>:
> 4b0: 55 push %ebp
> 4b1: bd 00 00 00 00 mov $0x0,%ebp
> 4b6: 89 e8 mov %ebp,%eax
> 4b8: 57 push %edi
> 4b9: 56 push %esi
> 4ba: 53 push %ebx
> 4bb: 83 ec 10 sub $0x10,%esp
> 4be: 8b 54 24 24 mov 0x24(%esp),%edx
> 4c2: 8b 0c 95 00 00 00 00 mov 0x0(,%edx,4),%ecx
> 4c9: 01 c8 add %ecx,%eax
> 4cb: 8b 50 0c mov 0xc(%eax),%edx
> 4ce: 85 d2 test %edx,%edx
> 4d0: 0f 84 ba 01 00 00 je 690 <dbs_check_cpu+0x1e0>
This is the "init_flag == 0" test:
> 4d6: 66 83 3d 10 00 00 00 cmpw $0x0,0x10
> 4dd: 00
> 4de: 8b 00 mov (%eax),%eax
> 4e0: 89 44 24 0c mov %eax,0xc(%esp)
> 4e4: 0f 84 ae 01 00 00 je 698 <dbs_check_cpu+0x1e8>
.......
This is
for_each_online_cpu(j) {
> 698: a1 00 00 00 00 mov 0x0,%eax
> 69d: 85 c0 test %eax,%eax
> 69f: 0f 84 e3 01 00 00 je 888 <dbs_check_cpu+0x3d8>
> 6a5: 0f bc c0 bsf %eax,%eax
> 6a8: 83 f8 03 cmp $0x3,%eax
> 6ab: bb 02 00 00 00 mov $0x2,%ebx
> 6b0: 0f 4c d8 cmovl %eax,%ebx
> 6b3: 83 fb 01 cmp $0x1,%ebx
> 6b6: 77 49 ja 701 <dbs_check_cpu+0x251>
> 6b8: 89 ee mov %ebp,%esi
> 6ba: 8d b6 00 00 00 00 lea 0x0(%esi),%esi
dbs_info = &per_cpu(cpu_dbs_info, j);
> 6c0: 8b 04 9d 00 00 00 00 mov 0x0(,%ebx,4),%eax
> 6c7: bf 02 00 00 00 mov $0x2,%edi
> 6cc: 01 f0 add %esi,%eax
> 6ce: 8b 00 mov (%eax),%eax
And this is the oopsing instruction:
> 6d0: 8b 40 1c mov 0x1c(%eax),%eax
> 6d3: 89 7c 24 04 mov %edi,0x4(%esp)
> 6d7: c7 04 24 00 00 00 00 movl $0x0,(%esp)
And this is the "requested_freq[j]" assignment:
> 6de: 89 04 9d 08 00 00 00 mov %eax,0x8(,%ebx,4)
> 6e5: 8d 43 01 lea 0x1(%ebx),%eax
> 6e8: bb 02 00 00 00 mov $0x2,%ebx
> 6ed: 89 44 24 08 mov %eax,0x8(%esp)
This is really a "call find_next_bit"
> 6f1: e8 fc ff ff ff call 6f2 <dbs_check_cpu+0x242>
> 6f6: 83 f8 03 cmp $0x3,%eax
> 6f9: 0f 4c d8 cmovl %eax,%ebx
> 6fc: 83 fb 01 cmp $0x1,%ebx
> 6ff: 76 bf jbe 6c0 <dbs_check_cpu+0x210>
And that wass the end of that loop:
> 701: 8b 4c 24 0c mov 0xc(%esp),%ecx
> 705: bb 01 00 00 00 mov $0x1,%ebx
> 70a: bf ff ff ff ff mov $0xffffffff,%edi
> 70f: 66 89 1d 10 00 00 00 mov %bx,0x10
And that was setting "init_flag = 1"
Horrid, horrid assembly language from that simple "for_each_online_cpu(j)"
loop. Oh, well.
Linus
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