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Re: [Qemu-devel] [PATCH] virtio-rng: correct the default limit rate

From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH] virtio-rng: correct the default limit rate
Date: Tue, 26 Nov 2013 08:32:30 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.1.0

On 11/26/2013 08:23 AM, Amos Kong wrote:

>> Hmm.  Libvirt is already converting a user's rate of bytes/period into
>> the qemu parameters, defaulting to 1 second as its default period.
> So libvirt will always pass a fixed 1 second period to qemu?

You forced me to check the code :)

We're safe.  Libvirt lets the user control both rate and period in the
XML.  If the user specifies neither, then libvirt doesn't pass max-bytes
or period (but that's the default for unlimited, and you argued that
even with your changes, the default is still effectively unlimited); the
same is true if the user specifies period but not rate (a different
period with no maximum is still effectively unlimited throughput, so it
didn't really matter that we don't pass period on through).  It is only
when the user specifies rate that libvirt passes anything on to qemu;
and in that case, libvirt always passes both max-bytes and period
(either with a period set by user, or with the period forced to 1000).

> Nothing need to do in Libvirt for _this patch_

Agreed.  Phew.

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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