48 lines
1.5 KiB
Plaintext
Executable File
48 lines
1.5 KiB
Plaintext
Executable File
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.
|
|
|
|
|