lartc.org FAQ :
Extremely inaccurate results using either TBF or HTB
There are reports on the LARTC mailing list that this can be resolved if you change
#define PSCHED_CLOCK_SOURCE PSCHED_CPUin linux/include/net/sched/pkt_sched.h. This is only useful if you have a CPU with timestamp counter (TSC). You can check this if you have "tsc" in the "flags" line in /proc/cpuinfo.
Kernel code and interface
Compile time switches
There is only one, but very important, compile time switch. It is not settable by "make config", but should be selected manually and after a bit of thinking inPSCHED_CLOCK_SOURCE can take three values:
- PSCHED_GETTIMEOFDAY
- PSCHED_JIFFIES
- PSCHED_CPU
PSCHED_GETTIMEOFDAY
Default setting is the most conservative PSCHED_GETTIMEOFDAY. It is very slow both because of weird slowness of do_gettimeofday() and because it forces code to use unnatural "timeval" format, where microseconds and seconds fields are separate. Besides that, it will misbehave, when delays exceed 2 seconds (f.e. very slow links or classes bounded to small slice of bandwidth) To resume: as only you will get it working, select correct clock source and forget about PSCHED_GETTIMEOFDAY forever.PSCHED_JIFFIES
Clock is derived from jiffies. On architectures with HZ=100 granularity of this clock is not enough to make reasonable bindings to real time. However, taking into account Linux architecture problems, which force us to use artificial integrated clock in any case, this switch is not so bad for schduling even on high speed networks, though policing is not reliable.PSCHED_CPU
It is available only for alpha and pentiums with correct CPU timestamp. It is the fastest way, use it when it is available, but remember: not all pentiums have this facility, and a lot of them have clock, broken by APM etc. etc.stef.coene@docum.org
Prio parameter