Re: [Xen-devel] Fwd: How to get real time in a xen vm?

[Meng Xu <xumengpanda@xxxxxxxxx>]

2015-04-28 22:46 GMT-04:00 Xuehan Xu <xxhdx1985126@xxxxxxxxx>:

---------- Forwarded message ----------
From: "Xuehan Xu" <xxhdx1985126@xxxxxxxxx>
Date: Apr 29, 2015 10:11 AM
Subject: How to get real time in a xen vm?
To: <xs-devel@xxxxxxxxxxxxxxxxxxx>
Cc:

Hi, everyone

Recently, I got a need to measure the latency of the I/O operation of TAPDISK on dom0, in comparison with that latency on a phyisical machine.

I tried to measure the latency by calling "gettimeofday" right before and after the io operation and compute the difference. But the time acquired by gettimeofday is a virtual time of the dom0, which makes it meaningless to compare to the latency on a physical machine.

How can I get the real and highly accurate time in dom0? Thanks:)

â

âYou may want to try the instruction 'rdtsc' âto read the timestamp counter register to get the latency.

Meng

--

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Meng Xu
PhD Student in Computer and Information Science
University of Pennsylvania

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