Messages in this thread Patch in this message | | | Date | Thu, 25 Aug 2016 11:22:14 +0200 | From | Borislav Petkov <> | Subject | Re: [LKP] [lkp] [x86/hweight] 65ea11ec6a: will-it-scale.per_process_ops 9.3% improvement |
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On Thu, Aug 18, 2016 at 06:11:39AM +0200, Borislav Petkov wrote: > So if there's no bug, alternatives should replace all "call > __sw_hweightXX" calls with POPCNT. So you shouldn't be even calling > these functions and hitting that path. > > Can you boot the kernel with "debug-alternative" and put that dmesg > somewhere along with vmlinux for me to stare at? Privately is fine too. > > I'd like to make sure the alternatives application actually happens.
Ok, Huang sent me the files I asked for privately (Thanks!). And I still can't see how that commit can even influence anything as the code doesn't get executed after alternatives:
ffffffff81007f35: e8 36 66 47 00 callq ffffffff8147e570 <__sw_hweight64> ffffffff81007f35: final_insn: f3 48 0f b8 c7 (popcnt %rdi,%rax)
ffffffff81008021: e8 4a 65 47 00 callq ffffffff8147e570 <__sw_hweight64> ffffffff81008021: final_insn: f3 48 0f b8 c7 (popcnt %rdi,%rax)
ffffffff8100bd63: e8 08 28 47 00 callq ffffffff8147e570 <__sw_hweight64> ffffffff8100bd63: final_insn: f3 48 0f b8 c7 (popcnt %rdi,%rax)
ffffffff81171a05: e8 66 cb 30 00 callq ffffffff8147e570 <__sw_hweight64> ffffffff81171a05: final_insn: f3 48 0f b8 c7 (popcnt %rdi,%rax)
ffffffff81171a66: e8 05 cb 30 00 callq ffffffff8147e570 <__sw_hweight64> ffffffff81171a66: final_insn: f3 48 0f b8 c7 (popcnt %rdi,%rax)
ffffffff8145c3e5: e8 86 21 02 00 callq ffffffff8147e570 <__sw_hweight64> ffffffff8145c3e5: final_insn: f3 48 0f b8 c7 (popcnt %rdi,%rax)
ffffffff8145c40c: e8 5f 21 02 00 callq ffffffff8147e570 <__sw_hweight64> ffffffff8145c40c: final_insn: f3 48 0f b8 c7 (popcnt %rdi,%rax)
ffffffff8174768d: e8 de 6e d3 ff callq ffffffff8147e570 <__sw_hweight64> ffffffff8174768d: final_insn: f3 48 0f b8 c7 (popcnt %rdi,%rax)
ffffffff817c43da: e8 91 a1 cb ff callq ffffffff8147e570 <__sw_hweight64> ffffffff817c43da: final_insn: f3 48 0f b8 c7 (popcnt %rdi,%rax)
ffffffff817f4e6a: e8 01 97 c8 ff callq ffffffff8147e570 <__sw_hweight64> ffffffff817f4e6a: final_insn: f3 48 0f b8 c7 (popcnt %rdi,%rax)
ffffffff81ffae4b: e8 20 37 48 ff callq ffffffff8147e570 <__sw_hweight64> ffffffff81ffae4b: final_insn: f3 48 0f b8 c7 (popcnt %rdi,%rax)
ffffffff82011bd1: e8 9a c9 46 ff callq ffffffff8147e570 <__sw_hweight64> ffffffff82011bd1: final_insn: f3 48 0f b8 c7 (popcnt %rdi,%rax)
__sw_hweight64 is at 0xffffffff8147e570 and all those locations which call 0xffffffff8147e570 get replaced with POPCNT (final_insn in dmesg).
Also, I did this to a guest kernel:
--- diff --git a/arch/x86/lib/hweight.S b/arch/x86/lib/hweight.S index 8a602a1e404a..7f18f59eadd5 100644 --- a/arch/x86/lib/hweight.S +++ b/arch/x86/lib/hweight.S @@ -34,6 +34,7 @@ ENTRY(__sw_hweight32) ENDPROC(__sw_hweight32) ENTRY(__sw_hweight64) + call dump_stack #ifdef CONFIG_X86_64 pushq %rdi pushq %rdx --- and got 23 invocations before alternatives get applied:
$ grep dump_stack ~/kvm/test-x86_64-1235.log | uniq -c 23 [<ffffffff81336955>] dump_stack+0x67/0x92 just to make sure that __sw_hweight64 *actually* *really* gets replaced.
Then I ran the job.yaml thing as suggested in the initial mail and no more __sw_hweight64 calls.
So either I'm still missing something or that's the wrong commit or ...
/me haz no idea :-\
-- Regards/Gruss, Boris.
ECO tip #101: Trim your mails when you reply.
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg) --
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