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Date: Thu, 29 Jan 2015 20:37:28 +0100
From: Marc =?UTF-8?B?TWFyw60=?= <marc.mari.barcelo@gmail.com>
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Subject: [Qemu-devel] QEMU and Real Time OS
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To: qemu-devel <qemu-devel@nongnu.org>

Hi

I tried to run a Linux Kernel with Preempt RT patch on a QEMU emulated
machine using TCG (ARM guest, x86_64 guest).

I expected the guest to have high latencies, but more or less constant.
But I found, using cyclictest, a lot of randomness and a lot of
difference between the average and the maximum latency.

I thought this may be due to I/O overhead. The current system has a root
filesystem through NFS, and I'm launching the tests through a serial
terminal and saving the results in files. But the high priority thread
saves the result in memory, it is the low priority thread that saves it
in files.

Is this an expected behaviour? I can't see why.

I'd like to know if there is a certain reason why it doesn't work. Or
if it should work and the problem is too much I/O overhead. Or any
other hint to understand it.

Thanks
Marc