Re: Nice 19 process still gets some CPU

[Con Kolivas <kernel@kolivas.org>]

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Timothy Miller wrote:
|
|
| Con Kolivas wrote:
|
|>
|> It definitely should _not_ starve. That is the unixy way of doing
|> things. Everything must go forward. Around 5% cpu for nice 19 sounds
|> just right. If you want scheduling only when there's spare cpu cycles
|> you need a sched batch(idle) implementation.
|>
|>
|
| Well, since I can't rewrite the app, I can't make it sched batch.  Nice
| values are an easy thing to get at for anything that's running.
|
| Besides, comparing nice 0 to nice 19, I'd expect something more like a
| 100:1 ratio or worse.  (That is, I don't expect nice to be linear.)
|
| Maybe this is just me, but when I set a process to the worst possible
| priority (nice 19), I expect it only to run when nothing else needs the
| CPU.


Sched batch is a kernel modification, and a simple wrapper will allow
you  to run _any_ program as sched batch without modifying it's source.

The design has had that ratio of 20:1 for a very long time so now is not
the time to suddenly decide it should be different. However if you want
to make it 100:1 for your machine feel free to edit kernel/sched.c
and change
#define MIN_TIMESLICE		( 10 * HZ / 1000)
to
#define MIN_TIMESLICE		( 1 * HZ / 1000)

That will give you more what you're looking for.

Con
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