On 07/18/2017 08:23 AM, Peter Krempa wrote:
On Mon, Jul 17, 2017 at 15:39:56 +0200, Michal Privoznik wrote:
This bugzilla is not public.
Okay, I'll drop it from the commit message.
Just like I've added support for setting rx_queue_size (in c56cdf259 and friends), qemu just gained support for setting tx ring size.
Signed-off-by: Michal Privoznik <mprivozn@redhat.com> ---
diff to v1: - Resend after 2e7d4916967 which introduced yet another qemu capability and thus made my patch not apply cleanly.
docs/formatdomain.html.in | 16 +++++++++++++++- docs/schemas/domaincommon.rng | 5 +++++ src/conf/domain_conf.c | 16 ++++++++++++++++ src/conf/domain_conf.h | 1 + src/qemu/qemu_capabilities.c | 4 ++++ src/qemu/qemu_capabilities.h | 3 +++ src/qemu/qemu_command.c | 8 ++++++++ src/qemu/qemu_domain.c | 16 +++++++++++----- ...e.args => qemuxml2argv-net-virtio-rxtxqueuesize.args} | 4 ++-- ...ize.xml => qemuxml2argv-net-virtio-rxtxqueuesize.xml} | 2 +- tests/qemuxml2argvtest.c | 5 +++-- ...e.xml => qemuxml2xmlout-net-virtio-rxtxqueuesize.xml} | 2 +- tests/qemuxml2xmltest.c | 2 +- 13 files changed, 71 insertions(+), 13 deletions(-) rename tests/qemuxml2argvdata/{qemuxml2argv-net-virtio-rxqueuesize.args => qemuxml2argv-net-virtio-rxtxqueuesize.args} (85%) rename tests/qemuxml2argvdata/{qemuxml2argv-net-virtio-rxqueuesize.xml => qemuxml2argv-net-virtio-rxtxqueuesize.xml} (93%) rename tests/qemuxml2xmloutdata/{qemuxml2xmlout-net-virtio-rxqueuesize.xml => qemuxml2xmlout-net-virtio-rxtxqueuesize.xml} (96%)
diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in index c12efcf78..58662cf48 100644 --- a/docs/formatdomain.html.in +++ b/docs/formatdomain.html.in
[...]
@@ -5201,6 +5201,20 @@ qemu-kvm -net nic,model=? /dev/null <b>In general you should leave this option alone, unless you are very certain you know what you are doing.</b> </dd> + <dt><code>tx_queue_size</code></dt> + <dd> + The optional <code>tx_queue_size</code> attribute controls + the size of virtio ring for each queue as described above. + The default value is hypervisor dependent and may change + across its releases. Moreover, some hypervisors may pose + some restrictions on actual value. For instance, latest + QEMU (as of 2017-07-13) requires value to be a power of two + from [256, 1024] range. + <span class="since">Since 3.6.0 (QEMU and KVM only)</span><br/><br/>
This is ridiculous. Since we can't figure out how to set this, how are users supposed to figure this out?
Well, you've cut off the line that reads; <b>In general you should leave this option alone, unless you are very certain you know what you are doing.</b> So only users that know how virtio works under the hood are expected to also know what rx/tx queue size is and how to set it. But frankly, I think users setting this are always gonna go with the highest value avaliable (1024). Such detailed description is a copy of rx_virtio_queue size description which is result of review.
Is it really needed? How should it be configured? Can't we or qemu pick a sane value?
No. Some users need bigger virtio rings otherwise they see a packet drop. So this is a fine tuning that heavily depends on the use case. Thus libvirt should not try to come up with some value. Michal