[libvirt] problem with outbound limiting

[Eric Blake]

On 08/10/2011 09:04 AM, Stefan Berger wrote:
> On 08/10/2011 02:55 AM, Upendra Moturi wrote:
>
> Hi,
>
> does this patch solve your problem? I am setting the MTU to fixed 2kb.
> Doing tests with scp seems to indicate that this improved the situation
> -- at least for me.
>
> Stefan
>
> Signed-off-by: Stefan Berger <stefanb at linux.vnet.ibm.com>
>
> ---
> src/util/network.c | 16 ++++++++--------
> 1 file changed, 8 insertions(+), 8 deletions(-)
>
> Index: libvirt-acl/src/util/network.c
> ===================================================================
> --- libvirt-acl.orig/src/util/network.c
> +++ libvirt-acl/src/util/network.c
> @@ -1156,8 +1156,8 @@ virBandwidthEnable(virBandwidthPtr bandw
>
> virCommandFree(cmd);
> cmd = virCommandNew(TC);
> - virCommandAddArgList(cmd,"class", "add", "dev", iface, "parent",
> - "1:", "classid", "1:1", "htb", NULL);
> + virCommandAddArgList(cmd,"class", "add", "dev", iface, "parent",
> + "1:", "classid", "1:1", "htb", NULL);
> virCommandAddArgList(cmd, "rate", average, NULL);

This hunk was just indentation; you should push the whitespace changes 
as a separate commit (and can push that now, under the trivial rule, 
without needing further review).  [It doesn't help matters that 
thunderbird botched the whitespace in my reply]

> @@ -1202,7 +1202,7 @@ virBandwidthEnable(virBandwidthPtr bandw
> virCommandAddArgList(cmd, "filter", "add", "dev", iface, "parent",
> "ffff:", "protocol", "ip", "u32", "match", "ip",
> "src", "0.0.0.0/0", "police", "rate", average,
> - "burst", burst, "mtu", burst, "drop", "flowid",
> + "burst", burst, "mtu", "2kb", "drop", "flowid",
> ":1", NULL);

Here's the meat of the proposed patch.  Is 2kb always valid, or will we 
run into problems on NICs that insist on traditional limits near the 
1518 mark?  Should it be user-configurable?  I'm reluctant to ACK this 
without a bit more understanding of why 2kb works, as well as feedback 
on test results with the patch in place.

-- 
Eric Blake   eblake at redhat.com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org