From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: Measuring KVM Performance using Hardware Performance Counters
Date: Sun, 02 Feb 2014 12:37:09 +0100
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To: Xin Tong <xerox.time.tech@gmail.com>, kvm@vger.kernel.org
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Il 02/02/2014 03:08, Xin Tong ha scritto:
> I am getting very weird profile results by running operf on linux on
> the host and profiling the a kvm virtual machine running dacapo
> eclipse benchmark.  I am expecting a lot of time should be spent in
> the qemu-system-x86_64 as the instructions from the eclipse benchmark
> would be treated as part of the qemu-system-x86_64 process, but the
> results tell different. any suggestions ?

Most of the time should be spent running the guest.  This is in the 
context of process qemu-system-x86_64, but it is not running code from 
the qemu executable.

What likely happens is that when the profiling counter expires, it 
causes the VM to exit before the profiling interrupt is delivered.  The 
sample should then be associated to the kvm_intel module.

31.5% in the KVM module seems like a lot.  Can you detail the results 
further, so that I can see the function names for kvm and kvm_intel?

Paolo

>
> CPU_CLK_UNHALTED %     Module
>          Symbol/Functions
> 1054             31.49 /kvm
>          /kvm
> 645             19.27 /kvm_intel
>         /kvm_intel
> 248             7.41
> /home/xtong/qemu-kvm-1.2.0/install/bin/qemu-system-x86_64
> /home/xtong/qemu-kvm-1.2.0/install/bin/qemu-system-x86_64
> 215             6.42 /usr/lib/debug/boot/vmlinux-3.11.0-13-generic
>         native_write_msr_safe
> 101             3.02 /usr/lib/debug/boot/vmlinux-3.11.0-13-generic
>         native_read_msr_safe
> 93               2.78 /lib/x86_64-linux-gnu/libc-2.15.so
>         /lib/x86_64-linux-gnu/libc-2.15.so
> 77               2.30 /lib/x86_64-linux-gnu/libglib-2.0.so.0.3200.4
>          /lib/x86_64-linux-gnu/libglib-2.0.so.0.3200.4
> 65               1.94 /usr/lib/debug/boot/vmlinux-3.11.0-13-generic
>          __srcu_read_lock
> 48               1.43 /usr/lib/debug/boot/vmlinux-3.11.0-13-generic
>          __srcu_read_unlock
> 40               1.20 /usr/lib/debug/boot/vmlinux-3.11.0-13-generic
>          native_load_tr_desc
> 29               0.87 /usr/lib/debug/boot/vmlinux-3.11.0-13-generic
>          __ticket_spin_lock
> 25               0.75 /usr/lib/debug/boot/vmlinux-3.11.0-13-generic
>          guest_exit
> 21               0.63 /usr/lib/debug/boot/vmlinux-3.11.0-13-generic
>          native_load_gdt
> ...
> Thank you.