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Re: [libvirt] [PATCHv2 0/3] exposing busy polling support for vhost-net



On Mon, Jul 17, 2017 at 01:39:13PM +0200, Peter Krempa wrote:
> On Mon, Jul 17, 2017 at 07:27:24 -0400, sferdjao redhat com wrote:
> > From: Sahid Orentino Ferdjaoui <sahid ferdjaoui redhat com>
> > 
> > In version 2.7.0, QEMU introduced support of busy polling for
> > vhost-net [0]. To avoid paraphrasing original authors of that feature
> > and the purpose it I prefer to share a pointer [1].
> > 
> > This patch serie exposes throught the NIC driver-specific element a
> > new option 'poll_us'. That option is only available with the backend
> > driver 'vhost' and that because libvirt automatically fallback to QEMU
> > if the driver is not specified where that option is not available.
> > 
> > The option 'poll_us' takes a positive. 0 means that the option
> > is not going to be exposed.
> 
> We had a similar attempt to do this for disk polling, but that was
> rejected since it's not very straightforward for the users to tune this
> variable. I think this falls into the same category.
> 
> Here's the discussion for iothread polling:
> 
> https://www.redhat.com/archives/libvir-list/2017-February/msg01048.html

Yes, thanks for pointing that out. I do have the same objections to this
patch, as for the previous disk polling patch. I just don't think they
are practical for a appliction to use - they're too low level to expose
to sysadmins, and there's no obvious way for an application to pick
the right settings automatically. So I think we're best served by letting
QEMU pick defaults

Regards,
Daniel
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