Date: Sun, 17 Sep 2000 06:32:19 +1100 (EST) From: Bruce Evans <bde@zeta.org.au> To: Alexander Leidinger <Alexander@Leidinger.net> Cc: current@FreeBSD.ORG, jhb@FreeBSD.ORG Subject: Re: 100% system time? (SMPng on UP system) Message-ID: <Pine.BSF.4.21.0009170616550.362-100000@besplex.bde.org> In-Reply-To: <200009161501.e8GF13n01686@Magelan.Leidinger.net>
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On Sat, 16 Sep 2000, Alexander Leidinger wrote:
> dnetc runns with idprio 31, system cvsupped around Sep 16, 11 CEST from
> a german mirror (it contains the idle fixes: src/sys/kern/kern_idle.c,v
> 1.4), complete build{world,kernel}.
>
> ---snip---
> last pid: 1666; load averages: 1.10, 1.11, 1.03 up 0+00:51:21 16:54:14
Perhaps it really is a system process :-[. idprio on a pure cpu hog prevents
other user processes from running like a system process might do:
idprio 31 sh -c "while :; do :; done"
System processes actually hang the entire system until they complete:
dd if=/dev/random of=/dev/null bs=10m count=1
This takes 32 seconds on a Celeron 366 overclocked to 523, during
which time no other processes, including interrupt tasks, can run.
This is because the supergiant lock prevents context switching while
the i/o is being done. There is nothing special about /dev/random
here except that it has a low transfer rate.
Bruce
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