From owner-freebsd-current  Wed Mar  7  5:43:16 2001
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Date: Thu, 8 Mar 2001 00:42:39 +1100 (EST)
From: Bruce Evans <bde@zeta.org.au>
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To: Mark Murray <mark@grondar.za>
Cc: Maxim Sobolev <sobomax@FreeBSD.ORG>, dougb@FreeBSD.ORG,
	current@FreeBSD.ORG
Subject: Re: harvest_interrupt=YES slows down machine 
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On Wed, 7 Mar 2001, Mark Murray wrote:

> > > Apart from a ridiculously low maxusers (you have 10, I recommend 128),
> > > I'm not sure what the problem is.
> > 
> > I do not see why it is "ridiculously low". Even GENERIC recommends 32, while
> > this is a small system intended to be used by only one person, so I do not see
> > any problem with it. I never had any `out of descriptors' or `can't fork'
> > during my routine operations on this box (2.5 years).
> 
> Ok - then please leave it at 32.

I use 10 with no problems.

> If you want me to help you, please help me get good info.
> 
> It's very important to me _know_ wether this is a boot slowdown or
> a generic - assertions are not good enough, I need hard facts.
> 
> My own laptop (A Toshiba Libretto 110CT) does a make world in
> about 8 hours (and it always has). Interrupt harvesting has not
> made a noticable difference (I have not been keeping records, but
> an overnight build has not yet progressed into my breakfast).

Just do something that causes a lot of interrupts that go through the
random harvester.  E.g.:

    dd if=/dev/ad0 of=/dev/null

causes 7750 interrupts/sec here (on a Celeron 366 overclocked to
522).  The random task takes 100% of the available cpu cycles.  This
slows down cpu-bound processes by a factor of about 3.5.  With a block
size of 64k instead of the default of 512, this causes only 300
interrupts/sec.  The random task takes a measly 27% of the cpu to
process these.  It can apparently only handle about 10 interrupts/second
with a reasonable overhead (1%).

Interrupt harvesting doesn't make much difference to makeworld because
makeworld is cpu-bound.  I estimate it to be about 2% here (20 interrupts
per second for disk i/o to local disks.  It would be a lot more for nfs).

Bruce


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