Stephen Hemminger wrote:

>I noticed that the netem delay values are off if using 
>CONFIG_NET_SCH_CKL_CPU. For example, if the latency is set to 500ms
> a ping reports the time as much less (343ms).
>
>Requested	JIFFIES	GETTIMEODAY	CPU
>0		.1	.1		.1
>1		2	2		1
>5		5	6		4
>10		10	11		7
>100		98	101		69
>500		489	500		343
>1000		976	1000		685
>
>The 1ms value is affected by the clock granularity.  Larger jiffie values
>are inaccurate due to the optimization of using shift to do divide (ie 1024 > 1000).
>
>With CLK_CPU /proc/net/psched is:
>000005d9 00000400 000f4240 000003e8
>  
>

sch_netem's interface is in us, but it doesn't convert the values to 
psched_us.
psched_us differ from us with CLK_CPU or CLK_JIFFIES for most values of HZ.
This patch fixes the problem, but the best solution is to change the 
interface
and pass the time values as psched_us from userspace, as done with 
rate-tables
and I think CBQ. I should have done this for HFSC too, but unlike for 
sch_netem,
I think it's too late to change the interface.

Regards
Patrick