| Kernel code and interface. |
| -------------------------- |
| |
| * Compile time switches |
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| 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> |
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| PSCHED_CLOCK_SOURCE can take three values: |
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| PSCHED_GETTIMEOFDAY |
| PSCHED_JIFFIES |
| PSCHED_CPU |
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| PSCHED_GETTIMEOFDAY |
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| 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. |
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| PSCHED_JIFFIES |
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| 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. |
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| PSCHED_CPU |
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| 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. |
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