On 07/18/2017 08:23 AM, Peter Krempa wrote: > On Mon, Jul 17, 2017 at 15:39:56 +0200, Michal Privoznik wrote: >> https://bugzilla.redhat.com/show_bug.cgi?id=1462653 > > 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@xxxxxxxxxx> >> --- >> >> 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 -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
