From: "Du, Changbin" <changbin.du@intel.com>
To: peterz@infradead.org, mingo@redhat.com, acme@kernel.org,
alexander.shishkin@linux.intel.com, linux-kernel@vger.kernel.org
Cc: changbin.du@intel.com
Subject: Does perf-annotate work correctly?
Date: Tue, 12 Sep 2017 18:10:35 +0800 [thread overview]
Message-ID: <20170912101035.GA21638@intel.com> (raw)
[-- Attachment #1: Type: text/plain, Size: 6207 bytes --]
When a annotate a symbol, I find the annotated C source code doesn't match assembly code.
So I cannot determine which line of C code has much overhead withou gdb's help.
Here is a example result of function apic_has_interrupt_for_ppr() in kvm module.
│580 __clear_bit(KVM_APIC_PV_EOI_PENDING, &vcpu->arch.apic_attention); ▒
│581 } ▒
│ ▒
│583 static int apic_has_interrupt_for_ppr(struct kvm_lapic *apic, u32 ppr) ▒
│584 { ▒
0.88 │30: cmpb $0x0,0x91(%rdi) ▒
2.54 │ ↓ je 63 ▒
0.20 │ mov 0xa0(%rdi),%rcx ▒
│581 int highest_irr; ▒
│582 if (kvm_x86_ops->sync_pir_to_irr && apic->vcpu->arch.apicv_active) ▒
4.91 │ mov $0xe0,%eax x ▒
1.46 │45: mov %eax,%edx x ▒
0.02 │ sar $0x5,%edx x ▒
3.57 │ shl $0x4,%edx x ▒
3.34 │ movslq %edx,%rdx x ▒
1.25 │ mov 0x200(%rcx,%rdx,1),%edx x ▒
42.44 │ test %edx,%edx x ▒
0.01 │ ┌──jne 88 x ▒
3.48 │ │ sub $0x20,%eax x ▒
2.24 │ │ cmp $0xffffffe0,%eax x ▒
│586│apic_find_highest_irr(): ▒
│ │ ▒
│407│ /* ▒
│408│ * Note that irr_pending is just a hint. It will be always ▒
│409│ * true with virtual interrupt delivery enabled. ▒
│410│ */ ▒
│411│ if (!apic->irr_pending) ▒
│ │↑ jne 45 ▒
0.62 │63:│ mov $0xffffffff,%eax ◆
0.83 │ │ leaveq ▒
13.52 │ │← retq ▒
│6a:│ mov %esi,-0x4(%rbp) ▒
│ │ mov %rdx,%rdi ▒
│418│find_highest_vector(): ▒
│340│static int find_highest_vector(void *bitmap) ▒
│341│{ ▒
│342│ int vec; ▒
│343│ u32 *reg; ▒
│ │ ▒
│345│ for (vec = MAX_APIC_VECTOR - APIC_VECTORS_PER_REG; ▒
│ │→ callq *%rax ▒
│ │ mov -0x4(%rbp),%esi ▒
│343│ vec >= 0; vec -= APIC_VECTORS_PER_REG) { ▒
│344│ reg = bitmap + REG_POS(vec); ▒
│345│ if (*reg) ▒
0.05 │75:│ cmp $0xffffffff,%eax ▒
│ │↑ je 63 ▒
1.95 │ │ mov %eax,%edx ▒
1.45 │ │ and $0xf0,%edx
Look at the assembly code block where I have put a 'x' on the right. Apparently the
assembly code doesn't match the C source code arrounded. Let's look the correct disassemble
result from gdb:
340 for (vec = MAX_APIC_VECTOR - APIC_VECTORS_PER_REG;
0x000000000003b4e0 <+64>: mov $0xe0,%eax
342 reg = bitmap + REG_POS(vec);
343 if (*reg)
0x000000000003b4e5 <+69>: mov %eax,%edx
0x000000000003b4e7 <+71>: sar $0x5,%edx
0x000000000003b4ea <+74>: shl $0x4,%edx
0x000000000003b4ed <+77>: movslq %edx,%rdx
0x000000000003b4f0 <+80>: mov 0x200(%rcx,%rdx,1),%edx
0x000000000003b4f7 <+87>: test %edx,%edx
0x000000000003b4f9 <+89>: jne 0x3b528 <apic_has_interrupt_for_ppr+136>
341 vec >= 0; vec -= APIC_VECTORS_PER_REG) {
0x000000000003b4fb <+91>: sub $0x20,%eax
340 for (vec = MAX_APIC_VECTOR - APIC_VECTORS_PER_REG;
0x000000000003b4fe <+94>: cmp $0xffffffe0,%eax
0x000000000003b501 <+97>: jne 0x3b4e5 <apic_has_interrupt_for_ppr+69>
Compared to gdb, perf-annoate has messed up. is it a bug or just perf is not as perfect as gdb?
--
Thanks,
Changbin Du
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 473 bytes --]
next reply other threads:[~2017-09-12 10:16 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-12 10:10 Du, Changbin [this message]
2017-09-12 14:33 ` Does perf-annotate work correctly? Arnaldo Carvalho de Melo
2017-09-13 1:54 ` Du, Changbin
2017-09-26 6:06 ` Du, Changbin
2017-09-13 9:14 ` Du, Changbin
2017-10-13 10:15 ` Du, Changbin
2017-10-16 9:28 ` Jiri Olsa
2017-10-16 9:34 ` Du, Changbin
2017-10-16 9:30 ` Jiri Olsa
2017-10-16 9:35 ` Du, Changbin
2017-10-16 10:45 ` Jiri Olsa
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20170912101035.GA21638@intel.com \
--to=changbin.du@intel.com \
--cc=acme@kernel.org \
--cc=alexander.shishkin@linux.intel.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.