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Re: [Qemu-devel] How to lock-up your tap-based VM network
From: |
Jamie Lokier |
Subject: |
Re: [Qemu-devel] How to lock-up your tap-based VM network |
Date: |
Mon, 12 Apr 2010 22:49:47 +0100 |
User-agent: |
Mutt/1.5.13 (2006-08-11) |
Paul Brook wrote:
> > A major reason for this deadlock could likely be removed by shutting
> > down the tap (if peered) or dropping packets in user space (in case of
> > vlan) when a NIC is stopped or otherwise shut down. Currently most (if
> > not all) NIC models seem to signal both "queue full" and "RX disabled"
> > via !can_receive().
>
> No. A disabled device should return true from can_recieve, then discard the
> packets in its receive callback. Failure to do so is a bug in the device. It
> looks like the virtio-net device may be buggy.
I agree - or alternatively signal that there's no point sending it
packets and they should be dropped without bothering to construct them.
But anyway, this flow control mechanism is buggy - what if instead of
an interface down, you just have a *slow* guest? That should not push
back so much that it makes other guests networking with each other
slow down.
-- Jamie
Re: [Qemu-devel] How to lock-up your tap-based VM network, Blue Swirl, 2010/04/13