2004-04-16 04:56:59 +08:00
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Kernel code and interface.
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--------------------------
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* Compile time switches
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There is only one, but very important, compile time switch.
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It is not settable by "make config", but should be selected
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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
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PSCHED_JIFFIES
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PSCHED_CPU
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PSCHED_GETTIMEOFDAY
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Default setting is the most conservative PSCHED_GETTIMEOFDAY.
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It is very slow both because of weird slowness of do_gettimeofday()
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and because it forces code to use unnatural "timeval" format,
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where microseconds and seconds fields are separate.
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Besides that, it will misbehave, when delays exceed 2 seconds
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(f.e. very slow links or classes bounded to small slice of bandwidth)
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To resume: as only you will get it working, select correct clock
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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
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granularity of this clock is not enough to make reasonable
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bindings to real time. However, taking into account Linux
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architecture problems, which force us to use artificial
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integrated clock in any case, this switch is not so bad
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for schduling even on high speed networks, though policing
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is not reliable.
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PSCHED_CPU
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It is available only for alpha and pentiums with correct
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CPU timestamp. It is the fastest way, use it when it is available,
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but remember: not all pentiums have this facility, and
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a lot of them have clock, broken by APM etc. etc.
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