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Date:      Wed, 21 Jul 2021 23:43:13 +0100
From:      RW via freebsd-hackers <freebsd-hackers@freebsd.org>
To:        freebsd-hackers@freebsd.org
Subject:   Re: Periodic rant about SCHED_ULE
Message-ID:  <20210721234313.4708c58d@gumby.homeunix.com>
In-Reply-To: <5482bee3-e033-c605-b380-ca3493be7492@FreeBSD.org>
References:  <13445948-7804-20b4-4ae6-aaac14d11e87@m5p.com> <20210708101907.0be3a3c2@rimwks.local> <20210714164745.0128ea15@gumby.homeunix.com> <b24a2124-fd4a-0ae6-944e-4d39d590794c@heuristicsystems.com.au> <8239e474-fc36-b8aa-93b7-39197534cd30@heuristicsystems.com.au> <20210719013743.0590b1f2@gumby.homeunix.com> <5482bee3-e033-c605-b380-ca3493be7492@FreeBSD.org>

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On Mon, 19 Jul 2021 09:14:34 +0300
Andriy Gapon wrote:

> On 19/07/2021 03:37, RW via freebsd-hackers wrote:
> > I haven't got time to look into this in detail but from a cursory
> > examination it looks like there must be some kind of translation
> > between the PRI values seen in top and the priorities used in the
> > scheduler.  
> 
> Yes. top's priority is the real priority - 100.

The test for preemption is 

   pri <= preempt_thresh

I suspect that the defaults have been set up on the assumption of

   pri < preempt_thresh

With and without  FULL_PREEMPTION the defaults are 224 and 80
respectively. Both of these are one level outside a range. There may
possibly be a good reason for 80, but 224 means that one idle level is
included. 



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