Back to files

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 in <include/net/pkt_sched.h>

PSCHED_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.