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[Qemu-devel] Re: Slowdowns comparing qemu-kvm.git to qemu.git: vcpu/thre

From: Anthony Liguori
Subject: [Qemu-devel] Re: Slowdowns comparing qemu-kvm.git to qemu.git: vcpu/thread scheduling differences
Date: Mon, 08 Feb 2010 08:57:05 -0600
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On 02/08/2010 07:46 AM, Amit Shah wrote:

In my testing of virtio-console, I found qemu-kvm.git introduces a lot
of overhead in thread scheduling compared to qemu.git.

My test sends a 260M file from the host to a guest via a virtio-console
port and then computes the sha1sum of the file on the host as well as on
the guest, compares the checksum and declares the result based on the
checksum match. The test passes in all the scenarios listed below,
indicating there's no unsafe data transfer.

Repo               Time taken
-----              ----------
qemu.git<  1 m (typically 30s)
qemu-kvm.git>  16m
qemu-iothread        ~ 5m

That very likely suggests that there are missing qemu_notify_events() in qemu-kvm.git and you're getting blocked waiting for the next timer event to fire.

IOW, I assume that during the qemu-kvm.git run, the CPU isn't pegged at 100% whereas it is in qemu.git.


Anthony Liguori

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