On Tue, May 13, 2025 at 13:28:58 +0100, Daniel P. Berrangé wrote:
> On Tue, May 13, 2025 at 02:25:51PM +0200, Peter Krempa via Devel wrote:
> > From: Peter Krempa <[email protected]>
> >
> > While the queue count itself is not a guest visible property, libvirt
> > uses it to calculate the 'vectors' property of the 'virtio-net' device
> > which is ABI.
> >
> > Since we don't expose control of 'vectors' explicitly, consider 'queues'
> > ABI.
> >
> > Signed-off-by: Peter Krempa <[email protected]>
> > ---
> > src/conf/domain_conf.c | 11 +++++++++++
> > 1 file changed, 11 insertions(+)
Per your off-list suggestion I'll be adding a comment to the formula
in qemuBuildNicDevProps which calculates 'vectors' to state that it's
guest ABI and must not change:
if (net->driver.virtio.queues > 1) {
if (net->info.type == VIR_DOMAIN_DEVICE_ADDRESS_TYPE_CCW) {
/* ccw provides a one to one relation of fds to queues and
* does not support the vectors option
*/
mq = VIR_TRISTATE_SWITCH_ON;
} else {
/* As advised at https://www.linux-kvm.org/page/Multiqueue
* we should add vectors=2*N+2 where N is the vhostfdSize
*/
mq = VIR_TRISTATE_SWITCH_ON;
+ /* As 'vectors' is a guest-OS visible property and thus
+ * guest ABI this formula *MUST NOT* change */
vectors = 2 * net->driver.virtio.queues + 2;
}
}
>
> Reviewed-by: Daniel P. Berrangé <[email protected]>
>
>
> With regards,
> Daniel
> --
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