On 01/07/2016 07:48 AM, Michal Privoznik wrote:
> On 29.12.2015 02:09, Jim Fehlig wrote:
>> 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@xxxxxxxx>
>> ---
>> 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;
>> + }
>> +
> Interesting. I'd expect:
>
> x_nic->rate_bytes_per_interval = bytes_per_sec;
> x_nic->rate_interval_usecs = 1000*1000;
For the most part I mimicked the Xen code and wanted to stick with the default
interval of 50ms, which has been the default for a long time. It is even
mentioned in some old RHEL5 docs
https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/5/html/Virtualization/sect-Virtualization-Tips_and_tricks-Limit_network_bandwidth_for_a_Xen_guest.html
BTW, here is the Xen code that inspired this logic
http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=tools/libxl/libxlu_vif.c;h=0665e624dc178a6ca8058e04a7baacaf1475bd37;hb=HEAD#l131
rate_bytes_per_interval is set to (bytes/s * interval us)/1000000us
I guess we are saying the same thing, you're just setting interval to 1s (thus
rate_bytes_per_interval == bytes_per_sec) instead of the historical 50ms :-).
>
> I mean, if I understood the xl way of rate limiting correctly, one says
> how much bytes can be sent for how long. so for 1MB/s I'd expect to send
> 1024*1024 bytes each second.
>
> Or am I missing something?
Does the above explanation make sense? I might be missing something :-). CC'd a
few Xen tools maintainer just in case.
Regards,
Jim
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