From: Borislav Petkov <bp@suse.de>
To: Borislav Petkov <bp@suse.de>
Cc: "Huang, Ying" <ying.huang@intel.com>,
"H. Peter Anvin" <hpa@zytor.com>,
"Denys Vlasenko" <dvlasenk@redhat.com>,
"Peter Zijlstra" <peterz@infradead.org>,
"Brian Gerst" <brgerst@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
"Andy Lutomirski" <luto@amacapital.net>,
lkp@01.org, "Thomas Gleixner" <tglx@linutronix.de>,
"Linus Torvalds" <torvalds@linux-foundation.org>,
"Ingo Molnar" <mingo@kernel.org>,
"Ville Syrjälä" <ville.syrjala@linux.intel.com>
Subject: Re: [LKP] [lkp] [x86/hweight] 65ea11ec6a: will-it-scale.per_process_ops 9.3% improvement
Date: Thu, 25 Aug 2016 11:22:14 +0200 [thread overview]
Message-ID: <20160825092214.GA4643@nazgul.tnic> (raw)
In-Reply-To: <20160818041139.GA22101@nazgul.tnic>
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)
--
next prev parent reply other threads:[~2016-08-25 9:22 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-16 14:26 [lkp] [x86/hweight] 65ea11ec6a: will-it-scale.per_process_ops 9.3% improvement kernel test robot
2016-08-16 16:59 ` H. Peter Anvin
2016-08-16 17:16 ` Borislav Petkov
2016-08-16 23:09 ` H. Peter Anvin
2016-08-17 5:46 ` Borislav Petkov
2016-08-17 22:29 ` [LKP] " Huang, Ying
2016-08-18 3:45 ` Borislav Petkov
2016-08-18 3:54 ` Huang, Ying
2016-08-18 4:11 ` Borislav Petkov
2016-08-25 9:22 ` Borislav Petkov [this message]
2016-08-25 10:05 ` H. Peter Anvin
2016-08-25 11:45 ` Borislav Petkov
2016-08-25 20:07 ` H. Peter Anvin
2016-08-18 3:57 ` H. Peter Anvin
2016-08-17 6:48 ` Peter Zijlstra
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