Re: [libvirt] [PATCH 2/2] libxl: support vif outgoing bandwidth QoS

The libxl_device_nic structure supports specifying an outgoing rate limit based on a time interval and bytes allowed per interval. In xl config a rate limit is specified as "<RATE>/s@<INTERVAL>". INTERVAL is optional and defaults to 50ms. libvirt expresses outgoing limits by average (required), peak, burst, and floor attributes in units of KB/s. This patch supports the outgoing bandwidth limit by converting the average KB/s to bytes per interval based on the same default interval (50ms) used by xl. Signed-off-by: Jim Fehlig <jfehlig(a)suse.com&gt; --- src/libxl/libxl_conf.c | 39 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) diff --git a/src/libxl/libxl_conf.c b/src/libxl/libxl_conf.c index 23c74e7..6320421 100644 --- a/src/libxl/libxl_conf.c +++ b/src/libxl/libxl_conf.c @@ -1093,6 +1093,7 @@ libxlMakeNic(virDomainDefPtr def, { bool ioemu_nic = def->os.type == VIR_DOMAIN_OSTYPE_HVM; virDomainNetType actual_type = virDomainNetGetActualType(l_nic); + virNetDevBandwidthPtr actual_bw; /* TODO: Where is mtu stored? * @@ -1206,6 +1207,44 @@ libxlMakeNic(virDomainDefPtr def, #endif } + /* + * Set bandwidth. + * From $xen-sources/docs/misc/xl-network-configuration.markdown: + * + * + * Specifies the rate at which the outgoing traffic will be limited to. + * The default if this keyword is not specified is unlimited. + * + * The rate may be specified as "<RATE>/s" or optionally "<RATE>/s@<INTERVAL>". + * + * `RATE` is in bytes and can accept suffixes: + * GB, MB, KB, B for bytes. + * Gb, Mb, Kb, b for bits. + * `INTERVAL` is in microseconds and can accept suffixes: ms, us, s. + * It determines the frequency at which the vif transmission credit + * is replenished. The default is 50ms. + + * Vif rate limiting is credit-based. It means that for "1MB/s@20ms", + * the available credit will be equivalent of the traffic you would have + * done at "1MB/s" during 20ms. This will results in a credit of 20,000 + * bytes replenished every 20,000 us. + * + * + * libvirt doesn't support the notion of rate limiting over an interval. + * Similar to xl's behavior when interval is not specified, set a default + * interval of 50ms and calculate the number of bytes per interval based + * on the specified average bandwidth. + */ + actual_bw = virDomainNetGetActualBandwidth(l_nic); + if (actual_bw && actual_bw->out && actual_bw->out->average) { + uint64_t bytes_per_sec = actual_bw->out->average * 1024; + uint64_t bytes_per_interval = + (((uint64_t) bytes_per_sec * 50000UL) / 1000000UL); + + x_nic->rate_bytes_per_interval = bytes_per_interval; + x_nic->rate_interval_usecs = 50000UL; + } +