[PATCH 0/2] qemu: Set noqueue qdisc for TAP devices

Michal Privoznik mprivozn at redhat.com
Tue Oct 13 14:06:52 UTC 2020

On 10/13/20 3:09 PM, Daniel Henrique Barboza wrote:
> On 10/8/20 3:10 PM, Michal Privoznik wrote:
>> See 2/2 for detailed explanation.
>> Long story short - we can squeeze more bandwidth from TAP devices we
>> create for domains.
>> Michal Prívozník (2):
>>    virnetdev: Introduce virNetDevSetRootQDisc()
>>    qemu: Set noqueue qdisc for TAP devices
> Reviewed-by: Daniel Henrique Barboza <danielhb413 at gmail.com>

Thanks. Just before I merged these I realized that it will be a good 
idea to mock virNetDevSetRootQDisc() so that we don't run tc from the 
test suite. But the diff is really trivial:

diff --git i/src/util/virnetdev.h w/src/util/virnetdev.h
index 82943b8e08..dfef49938f 100644
--- i/src/util/virnetdev.h
+++ w/src/util/virnetdev.h
@@ -313,6 +313,7 @@ int virNetDevRunEthernetScript(const char *ifname, 
const char *script)

  int virNetDevSetRootQDisc(const char *ifname,
-                          const char *qdisc);
+                          const char *qdisc)

  G_DEFINE_AUTOPTR_CLEANUP_FUNC(virNetDevRxFilter, virNetDevRxFilterFree);
diff --git i/tests/qemuxml2argvmock.c w/tests/qemuxml2argvmock.c
index 9bf4357b66..b9322f4f2a 100644
--- i/tests/qemuxml2argvmock.c
+++ w/tests/qemuxml2argvmock.c
@@ -286,3 +286,11 @@ qemuBuildTPMOpenBackendFDs(const char *tpmdev 
      *cancelfd = 1731;
      return 0;
+virNetDevSetRootQDisc(const char *ifname G_GNUC_UNUSED,
+                      const char *qdisc G_GNUC_UNUSED)
+    return 0;

Hopefully, you are okay if I squash this to 2/2.

> Have you tried it out with older kernels? Reading the bug I understood
> that 4.2 and older (2015 kernels) does not have qdisc support and that you
> can, for example, test for NETIF_F_LLTX of the ETHTOOL_GFEATURES ioctl to
> verify it.

I didn't, but I had this on mind when writing patches and I made the 
whole thing best effort. Note that qemuDomainInterfaceSetDefaultQDisc() 
retval is not checked for => if setting noqueue fails (for whatever 
reason) then worst case scenario an error is printed into logs.

> I consider this to be a 'nice to have' that can be added in a follow up
> patch though, if applicable. By the way, do we have any documentation about
> "the latest Libvirt release will not care about N+ years old kernel/QEMU"?

I'm not sure what you mean. This perhaps?



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