[Xen-devel] RE: Performance overhead of paravirt_ops on native identified

["Xin, Xiaohui" <xiaohui.xin@xxxxxxxxx>]

What I mean is that if the binary of _spin_lock is like this:
(gdb) disassemble _spin_lock
Dump of assembler code for function _spin_lock:
0xffffffff80497c0f <_spin_lock+0>:      mov    1252634(%rip),%r11        # 
#0xffffffff805c9930 <test_lock_ops+16>
0xffffffff80497c16 <_spin_lock+7>:      jmpq   *%r11
End of assembler dump.
(gdb) disassemble

In this situation the binary contains a jump, the overhead is more than the 
call.

Thanks
Xiaohui

-----Original Message-----
From: Jeremy Fitzhardinge [mailto:jeremy@xxxxxxxx] 
Sent: 2009年5月22日 12:28
To: Xin, Xiaohui
Cc: Chuck Ebbert; Ingo Molnar; Li, Xin; Nakajima, Jun; H. Peter Anvin; Nick 
Piggin; Linux Kernel Mailing List; Xen-devel
Subject: Re: Performance overhead of paravirt_ops on native identified

Xin, Xiaohui wrote:
> Remember we have done one experiment with "jump", the result shows seems the 
> overhead is even more than the call.
>   

I don't think you had mentioned that. You're saying that a
call->jmp->ret is slower than call->call->ret->ret?

J

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