> On Mon, 02 Nov 2009 16:43:42 +0100
> Patrick McHardy <kaber@trash.net> wrote:
>
>> Ryousei Takano wrote:
>>> Hi Stephen and all,
>>>
>>> I have observed a HTB accuracy problem on the Linux kernel 2.6.30 and
>>> the Myri-10G 10 GbE NIC.
>>> HTB can control the transmission rate at Gigabit speed, however it can
>>> not work well at 10 Gigabit speed.
>>>
>>> I asked Stephen this problem at Japan Linux Symposium. He mentioned a
>>> HTB bug related to the timer granularity.
>>> I want to know what is happen, and what should be do for fixing it.
>>>
>>> Any comments and suggestions will be welcome.
>>>
>>> For more detail, please see the following page:
>>>
http://code.google.com/p/pspacer/wiki/HTBon10GbE
>> This is not an easy problem to fix. Userspace, the kernel and the
>> netlink API use 32 bit for timing related values, which is too small
>> to use more than microsecond resolution. All of them need to be
>> converted to use bigger types, additionally some kind of compatibility
>> handling to deal with old iproute versions still using microsecond
>> resolution is required.
>
> The existing API is a legacy mish-mash. The field is limited to 32 bits,
> but it might be possible to use a finer scale.
>
> Maybe if kernel advertised finer resolution through /proc/net/psched
> then table could be finer grained. This would maintain compatibility
> between kernel and user space. You would need to have new kernel and
> new iproute to get nanosecond resolution but older combinations would
> still work.
>
> The downside is that by using nanosecond resolution the rates are upper
> bounded at 4.2seconds / packet.
>
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