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Re: [Qemu-devel] How to measure guest memory access (qemu_ld/qemu_st) ti

From: YeongKyoon Lee
Subject: Re: [Qemu-devel] How to measure guest memory access (qemu_ld/qemu_st) time?
Date: Fri, 15 Jun 2012 02:10:32 +0000 (GMT)

I don't know much of instrumentation approach of Lluis, however, I had roughly estimated guest memory access (qemu_ld/st performance) overhead in legacy way last year.

My idea was indirect performance estimation by measuring the generated host instruction counts of qemu_ld/st and their execution counts.

For measuring execution counts of IR, I had add some legacy instrumentation IR when generating TB IRs in TCG.


The result was as follows (qemu_ld/st overhead when Linux of x86 guest booting on QEMU 1.0)

  - 1 qemu_ld/st IR -> 12 host instruction when fast path (TLB hit case)

  - qemu_ld execution count: 5.3%

  - qemu_st execution count: 4.8%


Therefore, the performance overhead of qemu_ld/st could be up to about 50% (10% execution count * 12 instruction) using following rough assumptions.

1. Most qemu IRs are translated into one host instruction respectively.

2. The CPU cycles of host instructions are equal.

3. Ignoring TLB miss case.



Principal Engineer

VM Team

Yeongkyoon Lee


S-Core Co., Ltd.

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